Scottish Natural HeritageCommissioned Report No. 379

Investigation into the causes of black-throated diver Gavia arctica breeding failure on Loch Maree, 2006–2009

C O M M I S S I O N E D R E P O R T

Commissioned Report No. 379

INVESTIGATION INTO THE CAUSES OF BLACK-THROATED DIVER Gavia arctica

BREEDING FAILURE ON LOCH MAREE, 2006-2009

(Contract no. 20698)

For further information on this report please contact:

Eoghain MacLean Scottish Natural Heritage Anancaun KINLOCHEWE IV22 2PD eoghain.maclean@snh.gov.uk

or

Dominic Sargent Scottish Natural Heritage The Governor’s House The Parade FORT WILLIAM PH33 6BA dominic.sargent@snh.gov.uk

This report should be quoted as:

Brown, L. J. 2010. Investigation into the causes of black-throated diver Gavia arctica breeding failure on Loch Maree, 2006 - 2009. Scottish Natural Heritage Commissioned Report No.379 (contract no. 20698).

This report, or any part of it, should not be reproduced without the permission of Scottish Natural Heritage.

This permission will not be withheld unreasonably. The views expressed by the author(s) of this report

should not be taken as the views and policies of Scottish Natural Heritage.

© Scottish Natural Heritage 2010.

COMMISSIONED REPORT

Summary INVESTIGATION INTO THE CAUSES OF BLACK-THROATED DIVER Gavia arctica

BREEDING FAILURE ON LOCH MAREE, 2006-2009

Commissioned Report No. 379 ((Contract no. 20698)

Contractor: Lorna J. Brown

Year of publication: 2010

Background

In 1994 Loch Maree was classified as a Special Protection Area (SPA) on account of its black-throated diver Gavia arctica population. At the time it held 10 breeding territories and up to eight breeding pairs per annum; the largest breeding population of black-throated divers on a single water body in the UK. Analyses of long-term breeding records showed that failure of breeding attempts increased over the last 20 years but no cause was readily discernable. In 2006 a pilot study used automatic cameras to investigate the causes of breeding failure during incubation. Following the success of the pilot project, a three year study of black-throated diver breeding failure on Loch Maree was initiated in 2007. This report presents the findings of both studies and provides recommendations for future monitoring and management. Main findings A total of 26 active diver nests were found between 2006 and 2009; 21 (81%) of these

nests produced two eggs and eight (31%) hatched both eggs successfully. The use of automatic cameras allowed the outcome to be determined for 20 of the 26

nesting attempts. Camera malfunction or discovery of nests post-failure prevented determination in the other six.

Of the 20 nests for which the outcome was determined, only eight (40%) hatched two eggs. Two (10%) were partially successful, hatching one egg, and ten (50%) failed completely.

Complete or partial nest failure was due to predation in eleven cases. The main predators identified were pine marten and otter, but hooded crow and raven caused nest failure on a small number of occasions. Only one nest failure was attributed solely to flooding.

For further information on this project contact: Eoghain Maclean or Dominic Sargent

Tel: 01445 760254 or 01397 704716, respectively For further information on the SNH Research & Technical Support Programme contact:

DSU (Policy & Advice Directorate), Scottish Natural Heritage, Great Glen House, Inverness, IV3 8NW. Tel: 01463 725000 or pads@snh.gov.uk

Table of Contents Page

1 INTRODUCTION.....................................................................................................................1

1.1 Distribution and population status of black-throated divers..................................................1

1.2 Legal status of black-throated divers. ..................................................................................1

1.3 Study background. ...............................................................................................................1

1.4 Objectives. ...........................................................................................................................2

2 METHODS ..............................................................................................................................2

2.1 Nest sites .............................................................................................................................2

2.2 Automatic cameras...............................................................................................................2

2.2 Multi-media card analyses....................................................................................................3

2.3 Direct observations of adults and chicks. .............................................................................3

3 RESULTS................................................................................................................................4

3.1 Limitations of the camera study............................................................................................4

3.2 Influence of camera presence on diver and predator behaviour. .........................................4

3.3 Total number of nesting attempts and hatching success .....................................................5

3.4 Causes of nest failure within individual diver territories. ......................................................6 3.4.1 Territory A. .....................................................................................................................6 3.4.2 Territory B. .....................................................................................................................6 3.4.3 Territory C. .....................................................................................................................7 3.4.4 Territory D. .....................................................................................................................7 3.4.5 Territory J.......................................................................................................................8

3.5 Predator behaviour...............................................................................................................8 3.5.1 Pine marten....................................................................................................................8 3.5.2 Otter. ..............................................................................................................................9 3.5.3 Hooded Crow. ..............................................................................................................10 3.5.4 Raven...........................................................................................................................11

3.6 Fledging success and possible chick predators.................................................................12

3.7 Causes of nest failure in the past.......................................................................................13

4 DISCUSSION........................................................................................................................14

4.1 Causes of nest failure ........................................................................................................14 4.1.1. Pine marten.................................................................................................................14 4.1.2. Otter ............................................................................................................................15 4.1.3. Corvids........................................................................................................................15

4.2 Causes of fledging failure...................................................................................................15

4.3 Influence of the research on predator behaviour. ..............................................................16

4.4 Considerations regarding future management strategies ..................................................17 4.4.1. Further pine marten monitoring...................................................................................17 4.4.2. Raft repositioning ........................................................................................................17 4.4.3. Raft canopies ..............................................................................................................18 4.4.4. Electric fields...............................................................................................................18 4.4.5. Ultrasound deterrent ...................................................................................................18 4.4.6. Chemical control .........................................................................................................19 4.4.7. Predator removal ........................................................................................................19

5 CONCLUSIONS AND RECOMMENDATIONS .....................................................................20

6 REFERENCES......................................................................................................................21

List of Figures Page Figure 1: Pine marten removing whole eggs from nest on raft in territory C…………………… . 7 Figure 2: Pine marten arriving on raft in territory C while adult diver was incubating……………9 Figure 3: Diver eggs low in nest cup before otter visit (left) and clearly visible after otter visit. . 9 Figure 4: Otter manipulating egg on raft in territory J…………………………………………….. 10 Figure 5: The egg before and after the diver attempts to incubate……………………………... 10 Figure 6: Hooded crow removing egg, territory C, 2008………………………………………..... 11 Figure 7: Incubating diver defends nest from hooded crow in territory A……………………. ... 11 Figure 8: Raven removing egg, territory B, 2009……………………………………………….... .12 Figure 9: Raven at abandoned egg, territory J, 2008…………………………………………….. 12 List of Tables Page Table 1 - Total number of chicks hatched each year from five years prior to and four years during the present study………………………………………………………………..…….... 5 Table 2 - Outcomes of all known diver nesting attempts from 2006 to 2009…………….…… ... 6 Table 3 - Outcome of chick rearing in nests with successful hatching…………………............ 13 Table 4 - Possible causes of nest failure in the five years prior to the present study…… ....... 14

Acknowledgements

Thank you to Eoghain Maclean at SNH for help and discussion throughout the project. This project could not have taken place without Alan Jackson’s boat skills. I am extremely grateful to Jim Brown and Norman Thomas who assisted with the field work. Many thanks to Nigel Butcher, RSPB, who provided and serviced the camera systems. Thank you to Eoghain Maclean, Kenny Nelson, Dominic Sargent, Hans Kruuk, Liz Balharry and Norman Thomas for comments.

1. INTRODUCTION

This report presents the findings of a three year study to identify the causes of breeding failure during incubation of black-throated divers Gavia arctica on Loch Maree, Wester Ross; it also includes the findings from a preliminary study in 2006.

1.1 Distribution and population status of black-throated divers.

The black-throated diver (hereafter also referred to as ‘divers’) has a northern Holarctic distribution and within Britain is at the extreme oceanic edge of its distribution. The international population is estimated to be 19,196 pairs, of which the majority occur in Finland (JNCC 2006). Overall, there has been no significant change in population size in Europe in recent years, although there is a slight trend of decreasing population size in some countries (JNCC 2006). Britain holds less than 1% of the international population, and most of the 200 known British pairs breed on single-territory lochs within the Scottish Highlands and Islands. Within Scotland, the population increased in the mid-20th century, as persecution decreased, but it has remained stable since the 1980s (JNCC 2006). Loch Maree is a large, relatively undisturbed oligotrophic freshwater loch with many wooded islands. In 1994 it was classified as a Special Protection Area (SPA) on account of its black-throated diver population. At the time of designation Loch Maree supported ten diver territories, and up to eight breeding pairs in any one year, making it the largest breeding population of black-throated divers on a single UK waterbody. As well as an SPA, Loch Maree is also a Site of Special Scientific Interest (SSSI), a Ramsar site, part of a Special Area of Conservation (SAC) and the Loch Maree Islands are designated as a National Nature Reserve (NNR).

1.2 Legal status of black-throated divers.

The black-throated diver is a ‘Species of European Conservation Concern’ and holds Amber Population Status; it is listed in Annex 1 of The Birds Directive (Directive 2009/147/EL of the European Parliament and of the council on the conservation of wild birds) as it is considered rare or vulnerable within the European Community; within the UK it is protected at all times through its naming on Schedule 1 of the Wildlife and Countryside Act 1981 (as amended). At the local level, the black-throated diver is a Wester Ross Biodiversity Action Plan ‘Priority Species’.

1.3 Study background.

Black-throated divers have been recorded from Loch Maree since 1889 and annual monitoring has occurred since 1986. For monitoring purposed the loch is divided according to the areas referred to as territories A to J, based on prior knowledge of breeding behaviour. Territories B, C, D and H are situated in and around the Loch Maree island complex. As raft-nesting divers fledge significantly more chicks than pairs using natural sites (Hancock 2000; Butterfield 2004) artificial breeding rafts were introduced as part of a long term conservation strategy. Between 1988 and 1992 rafts were installed at six of the 10 territories. A seventh raft was installed in territory G in March 2007. Concerns that diver productivity at Loch Maree had decreased since the early 1990s instigated an in-depth analysis of breeding success (Setchfield 2006). This analysis confirmed fears that there were indeed significant declines in both territory occupancy and fledged chick production between 1986 and 2005. The report suggested that the population could not be maintained at its current level unless fledging success increased. Although flooding was found to be a major cause of nesting failure at many natural nest sites, the incidence of flooding was not found to have increased during the time period analysed. Instead, the increase in nest failures appeared to be attributable to predation events. This was most noticeable for the first annual nesting attempt of raft-nesting pairs. A number of potential predators were suggested, including otters Lutra lutra, herring gulls Larus

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argentatus, lesser black-backed gulls Larus fuscus, greater black-backed gulls Larus marinus and crows Corvus corone cornix.

1.4 Objectives.

To identify the cause, or causes, of black-throated diver breeding failure during incubation using automatic cameras at nest sites.

To determine the cause, or causes, of failure at the chick rearing stage using direct observations of adults and chicks in conjunction with automatic camera images.

To provide recommendations for future monitoring and management.

2. METHODS

The fieldwork for this project was carried out under Scottish Natural Heritage (SNH) bird photography licence number 7992. When monitoring predation rates using automatic cameras it is possible to determine whether the camera itself is having an influence on the predation rates by monitoring predation rates for a small number of nests without cameras (Thompson et al. 1999). In the present study it was considered that the small number of nesting attempts each year would make an analysis of the influence of both predation rates and the influence of camera use on productivity extremely difficult. Therefore, it was agreed with SNH that in order to maximise the predation data this project would not investigate the possible influence of the cameras.

2.1 Nest sites.

Each year all potential black-throated diver breeding sites were monitored by SNH staff from early May. In 2006 and 2007 automatic cameras were installed within 24 hours of SNH staff identifying each active nest site. In 2008 and 2009 cameras were installed at three regular nesting sites before diver activity commenced and installed at further nest sites as breeding was confirmed. In 2007 two cameras were also installed on unoccupied rafts within territories D and H towards the end of the nesting season, when they were no longer needed for active nests. SNH have not recorded divers nesting on either raft for a number of years and were keen to determine predator use of the rafts. The cameras remained on the rafts for 21 days. In 2009 a camera was installed at a mallard Anas platyrhynchos nest on a diver raft in territory H. The mallards nest there regularly but had never succeeded in producing chicks. To minimise human disturbance to the nesting divers, the time between nest visits was maximised. Initially visits occurred every two to three days. The visits were reduced to between four to six days in 2008 and 2009. One natural nest site was visited once a week as there was less vegetation to trip the recording mechanism (see below). To ensure that eggs were not chilled or damaged visits were planned to avoid the most inclement weather. All sites were accessed using a 16 ft clinker built wooden boat fitted with a 5 hp petrol outboard engine.

2.2 Automatic cameras.

Each small (1cm X 2cm X 5cm) camera was mounted on a thin (1cm diameter) aluminium pole and both camera and pole were painted in camouflage colours. The camera head was surrounded by small infra-red light-emitting diodes (LEDs) to provide night-time illumination. The camera was placed approximately 40cm from the nest and was joined to a Data Recording Unit (‘Memocam’) by approximately one metre of buried waterproof cable. Both the Memocam and a 12 volt battery to power the system were placed in a hole inside a bag

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and covered with turf. From May 2008 the Memocam and battery were contained in a waterproof storage box placed in the hole and covered with camouflage netting. The system had a “Video Motion Detection” facility which allowed software in the Memocam to analyse the images captured by the camera. If change occurred in a selected portion of the field of view a series of images was recorded onto a 128 MB multi-media card in the Memocam. The card recorded four frames when motion was detected – one before and three after the event, with a 0.3 second delay between frames. Recording was suspended for 10 seconds before the next series of frames could be activated. The selected portion of the screen sensitive to motion was manipulated to prevent images being recorded by the incubating bird turning its head, in an attempt to reduce the number of images saved. However, if the card was not changed before all frames were filled, the card continued to record, rewriting over the first recorded frames. In 2008 256MB cards were introduced. The timer system within the Memocam should have allowed the time of each image to have been recorded. However, difficulties in the timer set-up dictated that the time of each card change had to be recorded manually to provide a correction factor for the stored data.

2.2 Multi-media card analyses.

The following parameters were recorded for each card downloaded:

Time recording commenced. Time the adult diver arrived to recommence incubation. Time and behaviour of any predator visiting a nest. Any behaviour of an adult diver which seemed unusual. Length of time for which adult divers left the nest unattended during incubation.

For the purposes of the study incubation was considered to start when the first egg was laid. Where the first egg had already been laid by the time a nest was discovered, date of discovery was used for the onset of incubation.

2.3 Direct observations of adults and chicks.

At an early stage in the project it was felt that automatic cameras provided sufficient information regarding incubation failure and as a consequence no direct observations of incubation were made. Although the contract was to examine incubation failure it was decided, after discussion with SNH, that camera information could be utilised in conjunction with direct observations to attempt to determine failure at the chick stage. Therefore, direct observations commenced after chicks had hatched. Observations focused on territories A and J where there was a history of failure. Watches were of two to six hours and involved continuous observation, using a 30X telescope, from a hidden vantage point. Initially, observations concentrated at dawn and dusk as this was thought the most likely time for predation to occur. However the observations were randomised throughout the day after the loss of chicks during daylight hours in 2008.

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3. RESULTS

3.1 Limitations of the camera study.

A number of factors led to loss of camera images. On arriving or departing from the nest adult divers occasionally knocked the camera out of alignment. They also moved the eggs outwith the section of screen sensitive to motion, this was especially noticeable at sites which were prone to flooding. Rough weather prevented planned camera downloads which increased the chance of battery failure. Periods of high wind also caused moving grass to trip the motion detector frequently. Despite attempting to make the systems waterproof, storms led to water ingress and camera failure. Towards the end of the study a small number of batteries started to become ineffective and discharged faster than previously. Images were also lost as a consequence of camera or card malfunction. In 2008 a new problem occurred as a consequence of unusually low water levels. Three nests sites were located on the shoreline of islands far from vegetation, in which the camera was usually concealed. Cameras were placed near the vegetation initially, to minimise disturbance, then moved closer on subsequent visits if possible. The distance between the camera and the nest prevented the LEDs from adequately illuminating all activity at the nest site during the hours of darkness. As a consequence one predation event was not recorded. Fortunately the predator was successfully identified as it passed close to the camera whilst approaching the nest.

3.2 Influence of camera presence on diver and predator behaviour.

No research visit to an active nest led to eggs being abandoned or chilled and indeed the study found that divers regularly left eggs unattended for long periods of time overnight without causing egg chilling and subsequent nest failure. One instance of predation occurred after researchers had visited the nest and before divers returned to incubate (Appendix 1, Code 14). Prior to this visit, the nest had been flooded, the diver had moved the egg outwith the range of the camera and diver activity had not been recorded. It is therefore impossible to determine whether the nest had already been abandoned as a consequence of flooding or whether the predation was linked to the research nest visit. During the study overall hatching success was accurately recorded in all years except 2009 when camera malfunction occurred within the hatching period for one nest. In the five years prior to the study it was not always possible to determine whether failure occurred towards the end of incubation or in the first days after hatching. Therefore hatching success is recorded as a minimum to maximum (Table 1). No large scale differences can be discerned between the hatching success prior to and during the study, suggesting the cameras did not increase or decrease the risk of predation to any obvious degree. Indeed comparing the mean no. of young fledged in the five years prior to the study with the mean number fledged during the study suggests that hatching success may have been slightly higher in the four years of the study.

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Table 1: Total number of chicks hatched each year from five years prior to and four years during the present study.

Year Before/During study Chicks hatched 2001 Before 4-6 2002 Before 2 2003 Before 3-4 2004 Before 2-4 2005 Before 4-5 2006 During 5 2007 During 5 2008 During 6 2009 During 3-5

3.3 Total number of nesting attempts and hatching success.

In total 26 nesting attempts, including multiple nesting attempts by pairs within one season, occurred during the four year study period. Of these, eight (31%) hatched all eggs within the clutch (Table 2, Attempts 1-8). Of the 26, two had already failed prior to detection by SNH staff and only fragments of shell remained (Table 2, Attempts 9 & 10). Cameras were set at the other 24. Despite the problems of working with cameras in this environment, the nesting outcome was ascertained for 20 nesting attempts. The causes of two complete and one partial nest failure were not ascertained due to aforementioned camera malfunctioning (Table 2, Attempts11-13). It is likely that one further failure occurred at young chick stage but this could not be verified as a camera failure caused the loss of images at the time of hatching (Table 2, Attempt 14). Of the 20 attempts with a known outcome, eight successfully hatched 100% of the clutch, two had partial hatching success (Table 2, Attempts 15 & 16) and 10 failed at the incubation stage (Table 2, Attempts17-26). Only one failure on an island site was caused by predation, while eight failures on rafts were attributed to predation. Fledging success is examined in section 3.6. To aid future research and reserve management the nest failures are examined firstly by individual territory and then by predator species.

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Table 2: Outcomes of all known diver nesting attempts from 2006 to 2009. Attempt Year Territory Nest Eggs laid Eggs lost Cause of failure

1 2006 J Raft 2 0 2 2006 A Island 2 0 3 2007 J Raft 2 0 4 2007 B Raft 2 0 5 2008 A Island 2 0 6 2008 B Raft 2 0 7 2008 J Island 2 0 8 2009 A Island 2 0 9 2009 G Raft 1 1 Before discovery 10 2007 D Island 2 2 Before discovery 11 2006 B Raft 2 1 Unknown -CF 12 2009 B Raft 2 2 Unknown -CF 13 2009 C Raft 2 2 Unknown -CF 14 2009 B Raft 2 ? Small chick stage? 15 2007 A Island 2 1 Egg not fertilised? 16 2009 J Raft 2 1 Otter 17 2008 C Raft 1 1 Crow 18 2008 C Island 1 1 Crow 19 2009 J Raft 1 1 Otter 20 2009 J Raft 1 1 Otter 21 2006 C Raft 2 2 Pine marten 22 2006 C Island 2 2 Flooding 23 2007 C Raft 2 2 Pine marten 24 2008 J Raft 2 2 Otter 25 2008 D Island 2 2 Pine marten 26 2009 B Raft 2 2 Raven / Otter

CF=camera failure

3.4 Causes of nest failure within individual diver territories.

3.4.1 Territory A.

The pair within territory A laid two eggs each year. None were lost to predators during incubation. One egg failed to hatch in 2007 and may not have been fertile.

3.4.2 Territory B.

In the years prior to the study, the pair of divers within territory B were the most successful in reaching the hatching stage, hatching six chicks in five years. During the study they hatched a minimum of five chicks from six breeding attempts. In 2006 one egg was lost and one hatched successfully. It was likely that the egg was lost as a consequence of the raft splitting up during a storm. The raft was replaced in 2007. The pair successfully hatched two chicks in 2007 and 2008. In 2009 partial failure first occurred when a raven removed one egg from a clutch of two (Appendix 1 Incident 13). Although the divers continued to incubate, otter activity lead to the loss of the second egg and, as at J, a diver was seen to remove the fragments of egg shell. A crow was observed on two occasions pecking at the egg remains. A second nesting attempt occurred at the same site on the raft. An otter ran across the nest one day after the first egg was laid but caused no damage. However the nesting attempt ended with one egg

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missing and one deserted (Appendix 1 Incident 15). A camera malfunction prevented identification of the cause of failure. A new camera was installed and a third nesting attempt occurred. It is not possible to ascertain whether the eggs from this third attempt failed before hatching or at the early chick stage as camera recording was erratic (Appendix 1 Incident 18). The behaviour of the adult divers when first observed following the disappearance of the eggs from the nest suggested that chicks were present but hidden. However chicks were not observed on any subsequent visit.

3.4.3 Territory C.

The pair within territory C did not produce chicks within the study period and have not been observed to produce chicks since 1994 (RSPB/SNH unpublished data). During the study they laid initially on a raft in all four years, moving to island sites after nest failure on the raft in 2006 and 2008. From 2006 to 2008 the raft was located in close proximity to Eilean Subhainn, where it was visited on a regular basis by a pine marten (see section 3.5). In both 2006 and 2007 a pine marten removed both eggs from the nest, within nine days and two days respectively of the first egg being laid (Appendix 1 Incidents 1 & 5). In 2008 a hooded crow removed the first egg within four hours of it being laid. It is likely that the pine marten would have again caused nest failure had the crow not arrived, as it was recorded on the raft 2 days later (Appendix 2 Incident 9).

Figure 1: Pine marten removing whole eggs from nest on raft in territory C.

In 2009 the raft was relocated some distance from Eilean Subhainn. Despite recording diver activity on the raft as early as the 24th of April, the first egg was not laid until the 5th of June. Nest failure occurred on the 28th of June. Unfortunately the camera did not record the cause of failure. The adult bird was recorded sitting on eggs in the early morning until 05:35. The next frame shows a diver examining the empty nest at 13:48. Fragments of shell were observed during the download visit (this is referred to in section 3.5.2 in relation to otter behaviour). On both occasions that divers nested on territory C islands they were unsuccessful. Severe flooding caused the entire island to be submerged in 2006 (Appendix 1 Incident 3). In 2008 flooding caused the divers to move the egg far up the beach to a small area of dry sand and the camera had to be realigned with the new nest site. The egg was removed by a crow 1 hour 11 minutes after this visit (Appendix 1 Incident 10). The divers had not returned to the nest within this time period and it is not clear whether they had already abandoned the egg due to the flooding.

3.4.4 Territory D.

Within territory D chicks were last produced in 1992. During the study period two unsuccessful nesting attempts were recorded in 2007 and 2008. The first failed before a camera could be installed. Placing a camera at the predated nest for 21 days post-failure did not help to determine the cause of failure or a possible predator. In

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2008 a camera was installed at an island clutch of two eggs. A pine marten was recorded travelling towards the nest two days later. A predation event was not recorded (see section 3.1) but the eggs were absent at dawn.

3.4.5 Territory J.

The pair of divers within territory J have had mixed hatching success, both during the study and in the years previous to this. In all years a raft nest location was favoured by the divers. In both 2006 and 2007 the divers successfully hatched two chicks despite visits to the nest by otter(s). In 2008 an otter disturbed the first nesting attempt which ended with a diver removing one egg and abandoning the other (Appendix 1 Incident 8). The second nesting attempt was successful. In 2009 a single egg was damaged during an otter visit within a day of laying (Appendix 1 Incident 11). The divers laid a second egg which was also damaged by an otter after five days of incubation (Appendix 1 Incident 12). The female later laid a clutch of two, one of which was also damaged after six days during an otter visit (Appendix 1 Incident 14). Otter behaviour is discussed in depth in Section 3.5.2. The divers continued to incubate the second egg which successfully hatched. On one occasion, an adult diver removed egg shell fragments from the nest after otter damage. On the other two occasions the damaged egg had been moved outwith the recording zone.

3.5 Predator behaviour.

3.5.1 Pine marten.

Pine martens were directly responsible for three nest failures (in territories C and D) and the loss of six eggs during the study period. All eggs were removed from the nest area and no remains were observed. In both 2006 and 2007 a pine marten arrived on raft C while the diver was still present and may have been attempting to attack the diver (Figure 2 and Appendix 2 Incident 1). Pine marten visits to raft C were also recorded prior to incubation and after predation (Appendix 2). A pine marten was responsible for the loss of eggs from a mallard nest on a raft in territory H. No images of pine martens were recorded by cameras to the south of Eilean Subhainn.

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Figure 2: Pine marten arriving on raft in territory C while adult diver was incubating.

3.5.2 Otter.

Otters were directly responsible for partial or complete nest failure in five clutches giving a loss of five eggs in total during the study period. Otters visited active raft nests a total of 20 times during incubation, yet only five (25%) of these visits led to egg damage and egg contents were possibly consumed on only one occasion. No eggs were removed from rafts and fragments of egg shell and contents often remained. Otters were recorded on rafts within territories B, C (old and new location), J and H. No otter activity was recorded from island sites or the disused raft in territory D. Otters visited rafts before incubation commenced, during incubation, between clutches and after chicks had hatched or the nest had failed (Appendix 3 and 4). Generally visits lasted two to three seconds but some were longer and are discussed in detail below. All visits occurred between the hours of dusk and dawn except one at 13:42. Of the 20 visits to active nests, five occurred after the adult bird had already left the nest and 14 caused the diver to leave. It was not clear for one occasion (Appendix 3). In both 2006 and 2007 otter activity was observed at raft nests within territories C and J during incubation but eggs were not damaged (Appendix 3). In 2008 otter activity was again observed at the rafts C and J. However in one instance the recorded activity lasted longer than on previous occasions and the otter disturbed the eggs in some way. The eggs were low in the nest cup before its arrival but were visibly higher in the nest cup after it departed (Figure 3 and Appendix 3 Incident 12). At first light an adult diver removed one egg from the nest and the other egg was later abandoned.

Figure 3: Diver eggs low in nest cup before otter visit (left) and clearly visible after otter visit.

In 2009 otter activity was recorded at active nests on raft J, at raft C in its new location and for the first time at raft B. Four of the eight visits consisted of the otter passing over the nest areas quickly. However the other four visits led to the loss of eggs. On one the otter manipulated the egg with its front paws, however it was not clear whether the egg was damaged by a tooth puncture or a claw puncture (Figure 4 and Appendix 3 Incident 14). The egg was not consumed in any way, appearing to be almost complete with only a possible small puncture to the bottom left (Figure 5, frame a and b). As the diver attempted to

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incubate, the egg collapsed (Figure 5, frame c). Although the diver removed fragments of the egg shell, an area of dried contents remained in the nest at the next download visit.

Figure 4: Otter manipulating egg on raft in territory J.

Figure 5: The egg before and after the diver attempts to incubate .

Frame a Frame b Frame c

On one occasion the otter ‘handled’ an egg for over a minute and may have consumed some of the contents (Appendix 3 Incident 15). On the other two occasions the otter quickly moved away from the camera and although it was not possible to determine whether the otter consumed any part of the egg, egg fragments remained on the raft. A partially developed embryo was also seen on the raft in Territory J (Appendix 3 Incident 16). Otters may have been responsible for three other nest failures in 2009 where the camera malfunctioned, including on the raft at its new location in territory C where fragments of egg shell were observed and the otter visited the raft before (Appendix 3 Incident 20) and after the predation event (Appendix 4 Incident 21).

3.5.3 Hooded crow.

Hooded crows were directly responsible for nest failure in two single egg clutches in territory C in 2008 (Appendix 5, Incidents 3 and 11). Prior to the first incident a hooded crow had been observed in the bay scavenging on a deer carcass. Less than five hours after the diver egg was laid, the crow removed the egg while the adult was absent (Figure 6 and Appendix 5 Incident 3). The second predation also occurred when the diver was not in attendance (see 3.4.1).

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Figure 6: Hooded crow removing egg, territory C, 2008.

Hooded crows were recorded visiting island nest sites on seven occasions while divers were incubating and on all occasions the diver defended its nest (e.g. Figure 7). Crows consumed an abandoned egg in territory A (Appendix 5 Incidents 1 and 2), and scavenged at a failed nest in territory B (Appendix 5 Incidents 13 and 14).

Figure 7: Incubating diver defends nest from hooded crow in territory A.

3.5.4 Raven.

A raven was responsible for partial nest failure in one clutch, removing one egg from a clutch of two. The divers in territory B had left the nest unattended for nine minutes when the egg was removed (Figure 8 and Appendix 6 Incident 2). Incubation recommenced within 1 minute and 18 seconds of the predation event. The other egg was later consumed by an otter. In 2008 a raven was also observed to hold in its beak an abandoned egg at the raft in territory J. However it did not remove the egg from the raft and the egg was still complete on the nest download visit (Figure 9 and Appendix 5 Incident 1).

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Figure 8: Raven removing egg, territory B, 2009.

Figure 9: Raven at abandoned egg, territory J, 2008.

3.6 Fledging success and possible chick predators.

Of the 11 nests where hatching occurred, complete fledging success occurred only for four clutches (Table 3). Of the other seven clutches to hatch, four had partial fledging success and three lost all chicks. Despite over 350 hours of visual observations of chicks, no chick predation was observed. However, images from automatic cameras suggest possible predators for three broods. In 2007 one chick was known to have disappeared from territory A within 24 hours of three hooded crows being observed nearby. In 2008 two chicks went missing in territory A between the hours of 07:40 and 20:36. The nest camera recorded a hooded crow present on the shoreline close to both adult divers at 15:48. In 2009, an otter was recorded passing over the territory J raft the night a chick was lost. On three separate occasions chicks of up to three weeks of age were lost. By this stage they were travelling large distances and were therefore difficult to monitor and the cause of death is unknown.

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Table 3: Outcome of chick rearing in nests with successful hatching.

Code Year Territory No. hatched

No. lost before

fledging

Age lost

Predator activity recorded

1 2006 J 2 0 2 2007 B 2 0 3 2008 B 2 0 4 2006 B 1 0 5 2007 J 2 1 21 days None 6 2008 J 2 1 21 days Otter over raft 9 days after hatching 7 2006 A 2 1 1 day None 8 2009 A 2 1 None 9 2008 A 2 2 5 days 1 hooded crow present day of

disappearance. 10 2009 J 1 1 4 days Otter over raft night of disappearance,

buzzard morning 11 2007 A 1 1 7 days 3 hooded crows (1 day before

disappearance).

In 2008, an otter was observed to visit both the shoreline and raft in territory J shortly after the family of divers was seen calling and travelling rapidly into the open water of the main loch away from their usual foraging area. The divers may have responded to calls from divers in a neighbouring territory. The visual observations also showed that small fish were fed to chicks on a regular basis in territories A, B and J.

3.7 Causes of nest failure in the past.

Using knowledge of predator behaviour gained during the present study it is possible to infer causes of failure for the clutches laid in the five years prior to this study. It is suggested that otters caused nest failure in six clutches as fragments of egg shell were discovered (Table 4). As in the present study, the raft site in territory J thus appears to have suffered a high level of otter damage in these years. Otter activity may also have caused nest failure at an island site in territory H. Pine martens may have been responsible for losses in up to eight nests where both eggs were removed or an obvious nest scrape was observed but eggs were never found. Although corvids also removed eggs in the present study they did not succeed in removing two eggs from a clutch and were therefore not considered to be the likely predator in the previous years. This may underestimate the role of corvids to some degree. Removal of damaged eggs has been recorded in many other species including tree swallows Tachycineta bicolour and is thought to reduce predation risks (Mallory et al. 2000). It may also lead to the misidentification of predatory species and previous studies have found that nest predators can not always be identified by nest contents post-predation (Lariviere 1999; Williams and Woods 2002). However, in the present study, after the adult diver had removed shell fragments from broken eggs, fragments of shell and patches of dried out egg content typically remained. Thus it was possible to determine whether the divers’ egg losses were due to the loss of whole or broken eggs. This gives some clue as to the possible predator.

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Table 4: Possible causes of nest failure in the five years prior to the present study. Code Year Territory Nest Eggs laid Eggs lost Remains of

egg shell recorded

Possible cause

1 2001 C Raft Only scrape seen No Pine marten 2 2002 C Raft Only scrape seen No Pine marten 3 2002 D Raft Only scrape seen No Pine marten 4 2002 H Island 2 2 Yes Otter 5 2002 J Raft 2 2 Yes Otter 6 2003 D Raft 2 2 No Pine marten 7 2003 J Raft 2 2 Yes Otter 8 2003 J Raft 1+ 1+ Yes Otter 9 2004 C Raft 2 2 No Pine marten 10 2004 D Raft Only scrape seen No Pine marten 11 2004 E Island 2 2 No Pine marten 13 2004 J Raft 2 2 Yes Otter 12 2005 C Raft 3 3 No Pine marten 13 2005 J Raft 2 2 Yes Otter 13 2005 J Raft 2 2 No Insufficient field

notes regarding egg loss

4. DISCUSSION

4.1 Causes of nest failure.

Over the course of the study it has become apparent that a number of predatory species play a role in loss of diver eggs in the study site. Prior to the present study concerns were raised that possible reduced food availability may increase diver foraging time, forcing them to leave eggs unattended and vulnerable to predation. What is evident from this study is that two of the main predators, otters and pine martens, are not depredating unattended nests but approach the nest while the diver is incubating.

4.1.1. Pine marten

The highest egg loss recorded during the study occurred as a consequence of pine marten predation. Pine martens were also responsible for the loss of one mallard nest during the study. In all instances the pine marten arrived at the nest site while the incubating bird was present, all eggs from the clutch were completely removed from the nest site and no remains were observed. A similar pattern of behaviour was recorded during an automatic camera study of pine marten predation on capercaillie Tetrao urogallus (Summers et al 2009). The regular pine marten visits recorded on rafts before and after nesting suggests that they were visiting traditional nest sites opportunistically rather than using the presence of the incubating adult as a cue. As a consequence the time lapse between laying and pine marten predation was relatively short. Eggs are known to be an important food source for pine martens when vole and mouse densities are low (Pulliainen and Ollinmaki 1996) and they have been recorded caching large eggs in the spring for consumption the following winter (Helldin 1999). All pine marten predation occurred within territories close to the large islands of Garbh Eilean and Eilean Subhainn and none of the diver nests found within this area have hatched chicks in the last ten years. Pine marten scats were observed on the shore of Garbh Eilean in 2008 but pine marten activity was not recorded out with this area. It is possible that they are resident on these two larger islands and regularly swim small distances (such as the 30m channel between Garbh Eilean and the small island used by divers in territory D) but do not

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swim the larger distance of 150m between Eilean Subhainn and islands to the west frequently. There is little recorded evidence of pine marten swimming abilities, making it difficult to determine how far the martens are likely to swim. Mech and Rogers (1977) found that a male Eastern pine marten (Martes americana americana) swam across a lake twice during a radio tracking study – covering a distance considered to be either 30 metres or 64 metres, depending on whether the marten had chosen to use the shortest crossing or took the most direct route between the two radio tracking locations.

4.1.2. Otter

Otters disturbed the largest number of clutches in the study and were possibly responsible for damaging eggs in further clutches where camera malfunction occurred. The otter activity did not appear to be an act of predation per se as eggs were unharmed in 75% of nest visits and in others were often slightly damaged but remained uneaten. In one other camera study, otters were recorded removing Slavonian grebe Podiceps auritus eggs at two of 23 nests during an automatic camera study (Hannock et al 2002, Perkins et al 2005); in one of those cases one egg was found crushed but complete near the nest. The arrival of American mink Mustela vison in the western isles of Scotland, where otters were already present throughout the area, was found to correlate highly with the decrease in nesting seabirds (Craik 1997), suggesting that otter predation on eggs was less frequent than the minks’; if indeed the otters were predating any eggs. If the otters were visiting rafts predominantly for intraspecific communication, i.e. utilising them as traditional spraint sites, then it would be expected that spraints would be found frequently on rafts. In fact spraints were rarely found and only seemed to be deposited when divers were not incubating. In a previous study, Brown and Macdonald (1995) found that canid predators appeared to visit turtle nests prior to a predation event, possibly reinforcing a ‘mental map’ of potential food sources. Scats were found at a significantly higher number of depredated nest sites than undisturbed nest sites, suggesting that the predators used the scats as a sign that the food source had been utilised. Red foxes Vulpes vulpes are also known to urinate on depredated nests as a “no food” sign (Henry 1977). It is more likely that the otters are visiting the rafts for a short rest to allow their fur to dry, improving the insulation capacity. Although otter activity was not recorded at island nest sites it is likely that otters are active throughout the full extent of the loch.

4.1.3. Corvids

Crow predation attempts were unsuccessful while an incubating diver was present with the diver managing to ward off the crow. On all three occasions where corvid predation occurred, the divers were not present at the nest site. It is possible that one of these occasions may have been caused by human disturbance and this is discussed further in 4.3. As the divers were recorded to leave nests unattended for prolonged periods of up to an hour during daylight it is perhaps surprising that crows do not take more eggs

4.2 Causes of fledging failure.

There is strong link between the presence of small fish such as minnows Phoxinus phoxinus and black-throated diver chick survival (Jackson 2002; 2005). Minnows occur throughout Loch Maree and adult birds were observed to feed small fish to chicks frequently during visual observations. It is therefore thought that chick survival was not dependant on food availability. However, many of the minnows observed around the shoreline of Loch Maree were infected with intestinal tapeworms (personal observation), possibly Lingula intestinalis. Minnows are the intermediate host for this species and their behaviour is radically changed

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by the infection, increasing their uptake by the definitive bird host (Hart and Reynolds 2002). Adult divers can have heavy tapeworm infestations (RSPB unpublished data cited in Jackson 2005) and it is possible that a high parasite load may have an impact on the viability of diver chicks. The observation of an otter on the evening a chick disappeared from territory J suggests that predation is playing some role in the loss of chicks. Otters have been recorded taking Slavonian grebe chicks from the nest (Perkins et al 2005) and are capable of taking adult seabirds by swimming underneath them and dragging them below the surface (Kruuk 1995). Otter predation on birds is recorded as being only occasional (Jenkins and Harper 1980), although one recent study found that the proportion of bird remains in spraints increased from 26% to 66% over a period of five years after the local eel population crashed (Kruuk, pers comm.). Although crows were observed on two occasions when chicks disappeared in territory A, it is not possible to determine whether their presence was linked to the loss of chicks. In the past, remains of two adult divers have been recorded in the nest of a pair of white-tailed eagles Haliaeetus albicilla within the study area. Adult predation during the breeding season may influence productivity if eggs or chicks are left unattended and vulnerable while the remaining parent feeds. Unfortunately it was not possible to determine whether they were scavenged or depredated in either instance.

4.3 Influence of the research on predator behaviour.

Where human activity causes temporary exposure of nests an increase in predation can occur (e.g. Major 1990). However both Goetmark et al (1990) and Kertell (1996) found no proof of elevated predation rates after short-term human disturbance in either black-throated divers or Pacific divers Gavia pacific. Loch Maree was once a world famous sea trout fishery and the divers bred successfully despite angling activity (E. MacLean pers. comm.). In the present study the only nest to be depredated after research-linked disturbance was also in the process of being flooded, so it was not possible to determine whether the disturbance caused the predation event. The use of automatic cameras to monitor predation rates can provide skewed results if the presence of the camera increases or decreases the predation risk. Summers et al (2009) surmised that approximately 40m of cable between cameras and batteries provided a cue for pine martens to locate capercaillie (Tetrao urogallus) nests. Herranz et al (2002) studied the influence of camouflaged and uncamouflaged cameras and found that chick survival rate was significantly higher for woodpigeon Columba palumbus nests with uncamouflaged cameras than for either nests with camouflaged cameras or nests without cameras. The avian predators were clearly wary of the uncamouflaged cameras. Many other studies have found no effect of a camouflaged camera on the risk of predation (e.g. Brown et al 1998, Farnsworth and Simons 2000, Pietz and Granfors 2000, Thompson et al 1999). No influence of camera presence was observed in a recent study of otter predation on Slavonian grebe eggs using the Memocam system (Perkins et al 2005). The low nest numbers and uncertainty of hatching success before and during the present study prevented a true analysis of the influence of the camera presence on predation rates. Cameras were on rafts or small islands and it is likely that the predator would already have been approaching the raft/island before it received any visual or olfactory cues that the camera was present.

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4.4 Considerations regarding future management strategies

The presence of four mammalian and avian predator species presents a challenge regarding future management. Although many different predator control techniques have been tested in the past (see Mason et al 2001 and Schmelzeisen et al 2004 for reviews) many can be discounted as they would disturb nesting divers. There are a number of approaches which have potential for reducing the predation on diver nests, including: Raft repositioning Raft canopies Electrical fields Ultrasound deterrent Chemical control- border treatments, chemical irritants, fear inducing chemicals and

taste aversive conditioning. Predator removal

The advantages and disadvantages of each approach are discussed below. The success of each approach will be highly dependent on the distribution and behaviour of each of the predatory species present within the study site. Although the present study has gathered some relevant information, further predator monitoring would help clarify which approaches would best suit the situation at Loch Maree.

4.4.1. Further pine marten monitoring

From current information it would appear that pine marten activity is limited to the area around the two largest islands and does not extent to Eilean na Creige Giubhais in the east or Eilean Ruraidh Mor in the west (SNH observations). It would be of benefit to ascertain whether the pine martens from Garbh Eilean and Eilean Subhainn utilise other islands within the complex and how frequently they travel to the mainland. It would also be advantageous to determine the size of the resident population. As the Loch Maree island complex is a difficult area in which to carry out fieldwork, satellite telemetry would be the most appropriate technique to determine pine marten behaviour (Broekhuizen 2006). Pine martens readily enter baited traps (Halliwell pers. comm.) and the use of trapping to attach telemetry collars may also provide a minimum density estimate for the population. Radio telemetry would be more difficult in the island situation and this approach may have to rely on automatic recording stations. Baited cameras could be a less expensive approach to determine which islands pine martens are utilising, however some caution would be necessary as martens may temporarily leave their usual habitat to investigate a source of food (Proulx and O’Doherty 2006). It would not be prudent to be encouraging pine martens into areas they have not frequented regularly in the past. Scat transects could determine presence but the island vegetation is dense and a lack of scats may not necessarily be an accurate reflection on pine marten presence/ absence. Pine martens readily utilise nest boxes as dens (Ahola & Terhivuo 1982; Lockie 1961) and it is advised that the goldeneye Bucephala clangula nest boxes on the islands are inspected.

4.4.2. Raft repositioning

It is possible that moving rafts to new locations within the island complex may reduce the pine marten activity in the short term. Studies in Norway found that pine marten predation on box-nesting Tengmalm's owl Aegolius funereus occurred in a non-random fashion as they were more likely to revisit nest boxes where predation events had take place in previous years (Sonerud 1985). Moving the boxes to new locations reduced predation rates in the following year (Sonerud 1993). However, the ability of the pine martens to locate the territory D nest site (on an island which has been used before but at a new location) suggests that

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even short term respite from pine marten predation may be difficult to achieve. Otters utilised the raft moved within terriritory C in the first season after the move, suggesting that moving rafts would have no influence on otter predation rates. No pine marten activity was recorded on the repositioned raft to the west of territory C, but further research is necessary to confirm whether this move will prevent marten predation in the long term. Moving rafts within territories D and H further out from the nearest island could possibly either prevent pine martens reaching it or make it undesirable to attempt to reach - there should come a point at which the energy the marten expends to travel to the raft outweighs any possible energy gain from eggs/chicks on which it may be able to feed. It is unclear at the moment what this distance would be. It is also likely that there would need to be a compromise between the distance the raft is moved from the shore to protect it from pine martens and, for example, the degree of shelter needed by the raft, the practicalities of re-mooring it, and of course the requirements of the divers. Corvids did not depredate nests while divers were incubating. It is possible that increasing boat traffic to Isle Maree may increase the risk of corvid predation for divers incubating on rafts in territories C and B, as more disturbance could result in the divers being off their eggs for longer periods of time.

4.4.3. Raft canopies

Raft canopies obscure nests from avian predators and are utilised on great northern diver Gavia immer rafts (DeSorbo et al 2008). Although this may reduce the risk of corvid predation, it is known to decrease the flushing sensitivity of the divers (DeSorbo et al 2008), only allows divers to depart in two directions and may therefore increase adult susceptibly to otter or pine marten predation.

4.4.4. Electric fields

Electric fencing has been successfully tested in control studies to prevent mammalian predation of shore nesting bird and pine marten predation on pheasant pens (Balharry and Macdonald 1999; Schmelzeisen et al 2004). Although it would be difficult to develop an electrical barrier to prevent pine martens and otters but allow divers on to the nest, one possible approach could be to cover the rafts with some form of electrified netting out with the diver breeding season. For any hope of success, both mammalian predators would have to continue to visit rafts throughout the winter months and learn to avoid rafts before breeding commenced. Recently, a form of aversive conditioning has been developed using collars which deliver a small shock to the predator if it comes within a certain distance of a transmitter (Mason et al 2001). This technology has been successfully tested on wolves Canis lupus wearing aversive collars and calves wearing a transmitting collar (Shivik and Martin 2000). Pine martens could be trapped and fitted with a collar and transmitters could be placed on all rafts. This form of control would be most effective if the population of pine martens consists of a small number of resident individuals. Whilst pine martens are relatively easy to trap, otters are notoriously difficult to capture and this control method is therefore unlikely to be useful in preventing otter damage to eggs.

4.4.5. Ultrasound deterrent

Ultrasound deterrent is commonly advertised as a form of fox deterrent. There is evidence that birds can not hear the ultrasonic wave lengths (Mason and Clark 1997) which would suggest that ultrasound deterrent could be used for mammalian predators without influencing

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the diver behaviour. However, effectiveness of ultrasound deterrent on mammalian predators has yet to be proven scientifically (Bomford and O’Brien 1990).

4.4.6. Chemical control

Chemical repellents work in a number of ways, causing irritation, sickness or stimulating fear. In the past Renardine has been used to repell mammalian predators with varying success (Atkinson and Macdonald 1994; Vilardell 2008; Zemlicka and Mason 2000). Renardine is now illegal and although alternative products are advertised as effective fox repellents (‘Scoot’, ‘Get off my garden’ and ‘Wash and get off’), there is very little literature to back up their claims. Brown and Birks (2006) suggest the use of rags soaked with dog urine to deter pine martens from entering buildings, however there is no evidence to show that urine samples from one predator are actively avoided by others (Mason et al 2001). Irritants, such as capsicum oleo resin, can be successful in short term mammalian control, however the unwanted behaviour resumes as the irritant dissipates (Mason et al 2001). Aversive conditioning using substances that induced vomiting has been tested to curtail egg predation by a number of predators, including corvids, with success (reviewed in Conover 1995 and Mason 2001, Avery et al 1995; Bogliani and Bellinato 1998; Dimmick and Nicolaus 1990; Semel and Nicolaus 1992). Aversion remained between years when used for raccoons Procyon lotor and treated females denied their offspring the opportunity to become familiar with egg prey (Semel and Nicolaus 1992). Aversive conditioning is most successful where the chemical containing mimic is introduced to the predator species before the natural prey, allowing the conditioning to develop. A significant reduction in losses can occur if the eggs containing the chemical are similar to the eggs to be protected and alternative foods are readily available (Mason 2001). Diver eggs are only one of a number of food items available to the predatory species present at Loch Maree. Introducing experimental eggs before the divers start to breed would improve the success of the aversive conditioning and reduce the disturbance to the divers. If there are few resident pine martens within the island complex, all having access to the experimental eggs, then aversive conditioning may be successful in reducing pine marten predation. Aversive conditioning may not be successful with otters as they do not appear to consume the eggs. Problems occur with aversive conditioning when the predator species is able to discern the difference between the fake and natural eggs (Conover 1995) and therefore the most effective chemical and the most similar eggs to use would have to be researched thoroughly.

4.4.7. Predator removal

Predator removal is one of the oldest means of controlling predation and is increasingly used to protect prey species of conservation importance (e.g. Balser et al 1968). Predator control experiments have had varying degrees of success. For example, nesting success does not increase if there is compensation predation by other species (reviewed by Holt et al 2008, e.g. Parker 1984) or may only increase for one season, reducing when predator removal ceases (Harding et al 2001). The success of the removal of pine martens would be dependent on both the ability of martens on the neighbouring mainland to fill the vacant habitat and changes in the behaviour of the other predatory species present. Crows are known to target prey nest sites within close proximity to their own nests sites (Erikstad et al 1982) and selective removal of crows has been shown to increase the hatching success of the prey species (Erikstad et al 1982; Stien 2008). Controlling both crows and pine martens may be more successful than controlling one species alone (Holt et al 2008). Any possible predator management would need to take account of the conservation status of the predator species. Otters are listed in Annexes II and IVa of the European Habitats Directive (Council Directive 92/43/EEC on the conservation of natural habitats and of wild

19

fauna and flora), requiring the UK to encourage the management of features of the countryside which promote otter conservation, and they are afforded legal protection in the UK under Schedules 5 and 6 of the Wildlife and Countryside Act 1981 (as amended). The otter is also listed in both the UK Biodiversity Action Plan and the Wester Ross Local Biodiversity Action Plan as a “Priority Species”. The pine marten is listed in Annex V of the European Habitats Directive, and in Schedule 6 of the Wildlife and Countryside Act 1981 (as amended), giving it partial protection.

5 CONCLUSIONS AND RECOMMENDATIONS

It has become apparent over the course of the study that predation is having a long term influence on the nesting success of divers within the main island complex. As a consequence of both predation and flooding there has been no fledging success in the past nine years in territories C, D, E and H on either raft or natural sites. Sample sizes were small during this study and the presence of a deer carcass is likely to have increased crow activity within territory C in 2008, when crows were responsible for egg loss at two territory C nests. Only a longer term study could evaluate which predators are having the highest impact in this area. The study has also shown that although otters and corvids have a role in nest failure in nests outwith this central area, diver pairs affected by these predators were able to fledge some chicks in some years. Long lived species such as divers do not need a high annual chick survival rate to sustain the breeding population, and 0.4 to 0.5 fledged young per adult per year may be all that is necessary (Nilsson 1977). Out of ten potential territories, only 11 chicks reached fledging in the four years of the study, giving a fledging rate of 0.3 young per potential pair per year. This rate would not be sufficient to sustain the population as it stands and also produce sufficient adults to recolonise the increasing number of empty territories.

From the present study a number of recommendations for future research and management are suggested. Clearing vegetation to create small access points for divers on rafts D and H may

improve nesting success, however divers have used vegetated rafts in the past (E. Maclean, Pers. Comm.).

Relocate rafts within territories D and H as distant from the two main islands as is feasible.

Monitor nesting activity on rafts C, D, G and H using cameras in 2010. Examine goldeneye nest boxes for signs of pine marten activity. If utilised as pine

marten dens then remove or prevent marten access. Examine the population density, distribution and behaviour of the local pine marten

population. Monitor nesting crows within the island complex. Possibly relocate raft C further from the main boat route if future monitoring shows

nesting failure is influenced by human activity. Undertake a small scale study to compare predation rates between artificial nest sites

with and without camera systems.

Otter activity clearly influences nesting success; however no control methods would appear to be appropriate for the control of otter predation. Taste aversive conditioning or predator removal appear to be the most promising routes for pine marten and crow control and could be considered once further monitoring has occurred.

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Lariviere, S. (1999). Reasons why predators can not be inferred from nest remains. The Condor, 101, 718-721. Mackenzie, O. (1921). A hundred years in the Highlands. London: Geoffrey Bles. Major, R.E. (1990). The effects of human observers on the intensity of nest predation. Ibis, 132(4), 606-612. Mallory, M. L., Rendell W. B., & Robertson R. J. (2000). Responses of Birds to Broken Eggs in Their Nests. The Condor, 102, 673-675. Mason, J. R. (2001) Management alternatives relative to predators. In: T. F. Ginett, and S. E Henke, eds. The role of predator control as a tool in game management. San Angelo: Texas Agricultural Extension Sevice, Texas A&M University. Mason, J. R. & Clark, L. (1997). Avian repellents: options, modes of action and economic considerations. In Mason, J. R, ed. Repellents in wildlife management. CO: Colorado State University Press. Mason, J. R., Shivik, J. A., & Fall, M. W. (2001). Predation management. Chemical repellents and other aversive strategies in predation management. Endangered Species Update, 18(4), 175-181. Mech, L. D. & Rogers, L. L. Status, distribution and movement of martens in Northeastern Minnesota. USDA, For. Serv., North-Central For. Expt. Stat., Res. Pap. NC 143. Nilsson, S.G. (1977). Adult survival rate of the Black-throated Diver Gavia arctica. Ornis Scand., 8, 193-195. Parker, H. (1984). Effect of corvid removal on reproduction of Willow ptarmigan and Black grouse. Journal of Wildlife Management, 48(4), 1197-1205. Perkins, A. J., et al. (2005). Use of time-lapse video cameras to determine causes of nest failure of Slavonian Grebes Podiceps auritus. Bird Study, 52, 159-165. Pietz, P.L. & Granfors, D. A. 2000. Identifying predators and fates of grassland passerine nests using miniature video cameras. Journal of Wildlife Management, 64(1), 71-87. Proulx , G. & O’Doherty. (2006). Snow tracking to determine Martes winter distributions and habitat use. In: M. Santos-Reis et al, eds. Martes in Carnivore Communications. Sherwood Park, Alberta, Canada: Alpha Wildlife Publications. Pullianen, E. & Ollinmaki, P. (1996). A long term study of the winter food niche of the Pine maten Martes martes in northern boreal Finland. Acta Theriologica, 41, 337-352. Schmelzeisen, R., Prescott, D. R. C. & Engley, L. (2004). Methods for controlling depredation on Piping Plovers in Alberta: A literature review and synthesis. Alberta Species at Risk Report 84. Alberta, Alberta Environment , Alberta Sustainable Resource Development. Semel, B. & Nicolaus, L. K. (1992). Estrogen-based aversion to eggs among free ranging racoons. Ecological Applications, 2(4), 439-449. Setchfield, R. (2006). Black-throated Divers on Loch Maree: productivity trends and causes of failure. Unpublished report to SNH.

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Shivik, J. A. & Martin, D. J. (2000). Diversive and disruptive stimulus applications for managing predation. In Brittingham, M. C., Kays, J., and MacPeake, R., eds. The Ninth Wildlife Damage Management Conference Proceedings. 111-119. Sonerud, GA. (1985). Nest hole shift in Tengmalm's owl Aegolius funereus as defence against nest predation involving long-term memory in the predator. Journal of Animal Ecology, 54(1), 179-192. Sonerud, G. A. (1993). Reduced Predation by Nest Box Relocation: Differential Effect on Tengmalm's Owl Nests and Artificial Nests. Ornis Scandinavica, 24(3), 249-253 Stien, J. (2008). The role of the Hooded Crow (Corvus corone) in the nesting success of the Common Eider (Somateria mollissima) at two colonies in Troms county, Northern Norway. University of Tromsø. http://hdl.handle.net/10037/1615. Summers, R. W. Willi, J. & Selvidge, J. (2009). Capercaillie Tetrao urogallus nest loss and attendance at Abernethy Forest, Scotland. Wildlife Biology, 15, 1-9. Thompson, F. R., Dijak, W., & Burnhans, D. E. (1999). Video identification of predators at songbirds nests in Old Fields. The Auk, 116(1), 259-264. Vilardell, A. et al. (2008). Test of the efficacy of two chemical repellents in the control of Hermann’s tortoise nest predation. European Journal of Wildlife Research, 54(4), 745-748. Williams G. E. & Wood, P. B. (2002). Are traditional methods of determining nest predators and nest fates reliable? An experiment with Wood Thrushes (Hylocichla mustelina) using miniature video cameras. The Auk. 119(4):1126-1132. Zemlicka, E. D. & Mason, J. R. (2000). Response of captive Coyotes to Renardine Coyote Repellent. Proceedings of the Vertebrate Pest Conference, 19, 336-338.

Appendix 1. Causes of nest failure from 2006 to 2009. Incident Year Territory Nest Eggs

laid Eggs lost

Cause of failure

Days since 1st egg lay Time between diver departure and predator arrival

1 2006 C Raft 2 2 Pine marten 9 days On raft at same time 2 2006 B Raft 2 1 Unknown -CF 22 days Unknown 3 2006 C Island 2 2 Flooding 5+ days NA 4 2007 D Island 2 2 Before

discovery NA

5 2007 C Raft 2 2 Pine marten 2 days None 6 2007 A Island 2 1 Egg not

fertilised? NA

7 2008 C Raft 1 1 Crow 4.5 hours 2 hours 30 minutes 8 2008 J Raft 2 2 Otter 6 days 58 minutes 9 2008 D Island 2 2 Pine marten 2+ days Unknown 10 2008 C Island 1 1 Crow 24 days Unknown - flooding caused diver to move egg 11 2009 J Raft 1 1 Otter 1 day Unknown- nest to side of camera 12 2009 J Raft 1 1 Otter 5 days 4 hours 16 minutes 13 2009 B Raft 2 2 Raven / Otter 3 days / 14 days 9 minutes / 8 seconds 14 2009 J Raft 2 1 Otter 6 days 9 minutes 15 2009 B Raft 2 2 Unknown -CF 5+ days Unknown 16 2009 C Raft 2 2 Unknown -CF 23 days Unknown 17 2009 G Raft 1 1 Before

discovery NA

18 2009 B Raft 2 ? Small chick stage?

Unknown

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Appendix 2. Pine marten activity recorded at diver nest locations. Incident Date Nest Time diver

departs Time marten arrival

Length of visit Time between diver and marten

Time diver returns Stage of incubation

1 14/05/2006 C 23.45 23.45 5 visits over 33 minutes- predation

On raft together Four hours after last marten visit

9 days

2 01/06/2006 C NA 01.53 2 seconds NA NA 18 days after marten predation

3 09/06/2006 C NA 23.26 2 seconds NA NA 26 days after marten predation

4 18/05/2007 C NA 00.03 2 seconds NA NA Not started 5 23/05/2007 C NA 01.07 2 seconds NA NA Not started 6 08/06/2007 C NA 00.53 2 seconds NA NA Not started 7 16/06/2007 C 23.31 23.31 3 visits over 2

hours -predation On raft together 2 hours and 24 minutes

after last marten visit 2 days

8 03/05/2008 C NA 23:36 2 seconds NA NA Not yet started 9 09/05/2008 C NA 01:49 2 minute 15

seconds NA NA After predation by crow

10 18/05/2008 C NA 06:43 22 seconds NA NA After predation by crow 11 01/06/2008 D Unknown 02:26 Unknown -

predation Unknown Unknown 2+ days

12 22/04/2009 H Mallard on raft

22.44 2 visits - predation NA NA Unknown

13 23/04/2009 H NA 22.53 2 visits NA NA Unknown

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Appendix 3. Otter activity recorded at active diver nests. Incident Date Nest Time

diver leaves

Time otter arrives

Length of otter visit

Time between diver and otter

Time diver returns

Stage of incubation

Number of eggs damaged

1 06/05/2006 C 20.17 23.00 11 seconds 2 hours 43 minutes 05.18 on 07/05/06 1 day None 2 08/05/2006 C 21.52 21.54 2 seconds 2 minutes 03.04 on 09/05/06 3 days None 3 24/05/2006 J 23.00 23.01 2 seconds 1 minute 04.19 on

25/05/06 14 days None

4 28/05/2006 J 13.40 13.42 2 seconds 2 minutes 14.24 18 days None 5 28/05/2006 J 23.04 23.06 2 seconds 2 minutes 03.04 on 29/05/06 18 days None 6 29/05/2006 J 04.22 04.23 2 seconds 1 minute 05.33 19 days None 7 01/06/2006 J 22.44 23.47 2 seconds 1 hour 3 minutes 01.33 22 days None 8 05/06/2006 J 03.47 03.48 2 seconds 1 minute 04.26 26 days None 9 12/05/2007 J 04.40 04.41 2 seconds 1 minute 05.59 3+ days None 10 13/05/2007 J 02.09 02.09 2 seconds 16 seconds 03.02 4+ days None 11 11/05/2008 J 21.20 02.07

(12th) 2 seconds 4 hours 47 minutes 04.12 4 days None

12 13/05/2008 J 01.07 02.05 19 seconds 58 minutes 03.36 5 days One 13 03/05/2009 J unknown 21.17 3+ seconds ? ? 1 day One 14 09/05/2009 J 21.40 02.56 21 seconds 5 hours 16 minutes 04.12 5 days? One 15 15/05/2009 B 22.38 22.38 1 min 21

seconds 8 seconds 03.36 14 days One

16 27/05/2009 J 23.12 23.12 2 seconds 9 seconds 05.30 6 days One 17 31/05/2009 J 22.43 22.44 2 seconds 1 minute 41 seconds 04.04 10 days None 18 05/06/2009 B 00.28 00.28 2 seconds 19 seconds 02.42 6 days None 19 08/06/2009 J 01.51 01.51 3 seconds 9 seconds 03.01 18 days None 20 10/06/2009 C 23.10 23.20 2 seconds 10 minutes 23.32 4 days None

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Appendix 4. Otter activity recorded at rafts without diver nests. Incident Date Nest Time

arrival Length of visit

Relationship to diver activity

1 16/05/2006 C 21.43 2 seconds 2 days after marten predation 2 31/05/2006 C 01.22 4 minutes 7

seconds 17 days after marten predation

3 11/06/2006 J 22.24 18 seconds 2 days after hatching 4 11/06/2006 J 23.52 13 seconds 2 days after hatching 5 15/06/2006 C 21.13 2 seconds 32 days after marten predation 6 25/05/2007 C 23.58 2 seconds Not started 7 03/05/2008 J 01.18 2 seconds Not yet started 8 07/05/2008 J 04.00 2 seconds Not yet started 9 16/05/2008 C 00.45 12 seconds After predation 10 18/05/2008 C 09.50 9 seconds After predation 11 20/05/2008 J 00.56 2 seconds Abandoned egg not touched 12 26/05/2008 J 03.07 2 seconds Abandoned egg not touched 13 01/07/2008 J 02.07 4 minutes

31seconds 9 days after hatching

14 01/07/2008 J 02.51 1 minute 9 days after hatching 15 23/04/2009 H 01.43 12 seconds NA 16 14/05/2009 C 00.09 2 seconds Not yet started 17 21/05/2009 J 00.58 2 seconds Between clutches 18 23/05/2009 C 00.53 2 seconds Not yet started 19 26/05/2009 C 00.30 54 seconds Not yet started 20 22/06/2009 J 02.24 3 seconds 4 days after hatching 21 21/07/2009 C 03.15 2 seconds After predation

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Appendix 5. Crow activity recorded by cameras throughout the study. Incident Date Nest Time diver

leaves Time of crow arrival

Length of visit Time between diver and crow

Time diver returns Stage of incubation

1 22/07/2007 A island

Chick hatched, 1 egg left

19.07 13 minutes NA NA 6 days after chick hatches

2 23/07/2007 A island

Chick hatched, 1 egg left

5.22 Of and on for 7 hours NA NA 7 days after chick hatches

3 07/05/2008 C raft 17:47 20:16 3 minutes - Predation

2.5 hours 06:01 1st egg laid 15:50

4 21/05/2008 A island

Divers changing over

06:49 1 minute 9 seconds Still there- chases off Still there Incubating

5 22/05/2008 A island

Diver incubating 09:32 1 min 24 seconds Still there- turns to crow Still there Incubating

6 26/05/2008 A island

Diver incubating 14.36 3 seconds Still there- turns to crow Still there Incubating

7 28/05/2008 C island

Diver incubating 20.16 12 minutes Still there -turns Still there Incubating

8 08/06/2008 C island

Diver incubating 12:02 Only in view few seconds

Still there- turns to crow Still there Incubating

9 11/06/2008 C island

Diver incubating 20.06 Only in view few seconds

Still there- turns to crow Still there Incubating

10 12/06/2008 C island

Diver incubating 19.35 11 seconds Still there- turns to crow Still there Incubating

11 20/06/2008 C island

Crow removes egg 1 hour 11 minutes after camera is repositioned after flooding. Not sure why divers did not return within the time - nest abandoned?

12 11/06/2008 A island

Chicks hatched 15:48 2 crows top beach, 2 adult divers lower down beach, chicks not seen during next visual observation in the evening.

5 days after chick hatches

13 17/05/2009 B raft NA 06:06 3 minutes 43 seconds NA NA 2 days after egg predation 14 24/05/2009 B raft NA 18:48:00 22 seconds NA NA 9 days after egg predation

Appendix 6. Raven activity recorded by cameras throughout the study. Incident Date Nest Time diver

leaves Time arrival Length of visit Time between diver and raven Time diver returns Stage of incubation Eggs

taken/damaged 1 22/05/2008 J Not incubating 10:19 2 seconds Egg abandoned Lifted then left 2 04/05/2009 B 11:23 11:32 2 seconds 9 minutes 11:34 3 days 1 taken whole

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