Migratory restlessness in caged BramblingsFringilla montifringilla in northern Sweden

Heft 1 ] 65 1981 ]

]. Orn. 122, 1981: S. 65--72

Migra tory restlessness in caged Bramblings Frin&illa monti fr ingil la in nor thern Sweden

By Per Lundberg

Introduction

In recent years an increasing number of experimental investigations has been per- formed in the study of bird migration. In caged migrants one has been able to clarify several of the mechanisms underlying the phenomenon of bird migration. However, extensive studies on the migration in northern Europe with the experimental approach are scarce (c.f.e.g. STOLT 1977 a, b) although there are some descriptions of the gene- ral activity pattern of birds in northern latitudes. ASCHOFF et al. (1970) studied the activity pattern in the Chaffinch Fringilla coelebs at the arctic circle, and ANDERSSON & MOLLER (1978) and D~N (1972) both studied, among other bird species, the activity patterns in caged Bramblings, though without presenting any results on the migratory behaviour. Recently STOLT (1978) studied the night activity in Bramblings in constant conditions. In caged migrants, nocturnal activity during the natural migratory season has been interpreted as the expression of migratory restlessness (c.f. H~LMS 1963, BERT- HOLD 1973, 1975, KLEIN 1974). Accordingly the duration and intensity of migratory restlessness is proportional to the true migratory pattern of the free-living conspecifics. This seems to hold true at least for long-distance migrants (e.g. GWlNNER 1968 a, b, BZRTHOLD et al. 1972), but whether a generalization including short- and middle- distance migrants is valid is not yet fully clarified. In the present study, the migratory restlessness was quantified in caged Bramblings. The Brambling is a middle-distance migrant, breeding in northern Scandinavia, Finland and eastwards through the U.S.S.R. with its wintering grounds in southernmost Scandinavia and mid- and western Europe. In some years Bramblings winter as far south as northern Africa (DEMENTIEV & GLADKOV 1954, ERIKSSON 1970). The aim of this paper is to describe the migratory behaviour in the Brambling, with special reference to the daily and annual activity pattern. The photoperiodic and endogenous influence on the migration of the species will be discussed.

Material and methods

Six female Bramblings were caught a t HolrnOgadd Bird Observatory (60 ° 36'N, 20 ° 45'E) during their first autumn migration, and subsequently transferred to individual cages and kept indoors in a greenhouse at the University of Ume~t (63 ° 50'N). The birds were kept in constant temperature (15 ° C) and humidity but exposed to the natural photoperiodic variations throughout the experiment. The birds had visible and audible contact with each other in the experimental room but were not able to see anything from the surroundings of the experimental building. Two large semitransparent windows in the roof of the laboratory permitted the birds to detect the natural changes in light intensity during the day. As "daytime" was counted the period of the 24 hr-period with a light intensity above 5,0 lux, and as "night-time" the period below 5,0 lux.

[ J. Orn. 66 P. LUNDBERG [ 122

The experimental period lasted from mid-September 1977 to the end of May 1978. Locomotor activity of the birds was recorded by micro-switches connected with the perches in the cages. The number of jumps of individual birds per hour was recorded by an Elmeg print out counter. Food and water was present ad lib. The data on migratory time-table and phenology in the species is mainly based on ERIKSSON (1970) and own unpublished observations.

24 1~ ~ 12 Time of day Ihr)

Fig. 1. The daily activity pattern in the Bram- bling for five~representative periods during the course of the experiment. Shaded bars above each period indicate the night-length. For each period the mean values of the activity of the six birds is given with standard-

deviation.

Results

The daily activity patterns of the experimental birds show fairly good agreement with the expected patterns of the free-living conspecifics. In Fig. 1 the daily activity is shown for five representative periods during the course of the experiment.

During the natural migratory season in autumn (in Fig. 1; 17--30 September), the birds exhibit a well developed migratory restlessness during the night, with activity values reaching over 1000 jumps/hr around 22.00. The nocturnal activity is otherwise mainly (65 %) distributed before midnight. In the diurnal activity, the usual bimodal pattern (AscHorF 1966) is more or less absent during this time of the year. 15--30 January, when the species normally should have reached its wintering grounds, the experimental birds still show a fairly well developed nocturnal activity, at least in the early night (around 500 jumps/hr around 19.00). Furthermore, the amount of diurnal activity has decreased markedly since the early autumn period.

During the true winter season, activity is exclusively allocated to daytime. At this time of the year we also find the two-peak pattern of the diurnal activity. In the last periods described in Fig. 1, the migratory restlessness again appears and is fully developed during 10--25 May. The amount of activity during this period is very high. The morning peak reaches 3000 jumps/hr and a large part of the diurnal activity amounts to more than 2000 jumps/hr. In the afternoon the activity values decrease, but there is no pause between diurnal and nocturnal activity, which continues throughout the

Heft 1 ] 1981 ] Migratory restlessness in Bramblings 67

night. As in the autumn migratory period, the bimodal pattern of the diurnal activity is more or less absent.

In Fig. 2 the diurnal (Fig. 2 a) and nocturnal (Fig. 2 b) activity is plotted against the time of the year. From the figure, two phenomena are apparent. First the clear positive

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Fig. 2. a) Temporal course of the diurnal activity during the experimental period, expressed as jumps/hr. Mean values with their standard-deviation for the six birds in ten-day intervals is

plotted (above). -- b) As "a" but nocturnal activity (below).


correlation between the amount of diurnal activity and photoperiod (see also Fig. 3). Secondly, the two-wave pattern of the nocturnal activity and the refractory period in between during the winter. The two periods of nocturnal activity fit well to the natural migratory seasons of the species. However, two major discrepancies between the experimental birds and their free-living conspecifics are present. During the autumn period, the nocturnal activity is not terminated until around 15 January, i.e. well after mid- winter and when the species should have reached its wintering grounds. Secondly, the onset of spring migratory restlessness is delayed compared with the natural spring migratory period, and continues until the experiment was ended 25 May. The continuation of nocturnal restlessness that late in spring is beyond the natural migratory season, and it shows no tendency to decrease. It is even likely that the nocturnal restlessness would have continued until the post-nuptial moult in summer (c.f. GWI•NER & CZESCttLIK 1979).

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Fig. 3. The relationship between amount of diurnal activity and photoperiod. Points indicate activity means for ten-day intervals in the autumn (17 September -- 26 December) and triangles

spring (5 January - 25 May). r = 0.77, p < 0.001.

Discussion

In the experimental birds, the daily activity patterns differ markedly over different seasons (c.f. Fig. 1). During the migratory seasons the amount of diurnal activity is obviously higher than during the winter. Furthermore, the usual bimodal patern, nor-

Heft 1 Migratory restlessness in Bramblings 69 1981

mally shown by day-active animals (AscHOFr 1966) is practically absent in the diurnal activity during the migratory seasons. This might be explained by the fact that the Brambling does not migrate exclusively at night (e.g. ULFS'r~ND et al. 1974) and that at least a part of the migratory restlessness is distributed during daytime. The diurnal activity would therefore consist of the sum of the normal diurnal activity and the migratory restlessness. The problem of separating these two parts of the diurnal activity in diurnal migrants has been discussed by BERTHOLD (1978) and CZESCHLmK (1974), but there is still no clear method how to treat such data.

Several authors have dealt with the problem of the photoperiodic influence on bird migration, and it is now evident that photoperiod is a factor of critical importance for the control of onset and termination of the migration (BERTHOLD 1975, GWlNNER 1973, HELMS 1963, KENDEIGH et al. 1960, MERKEL 1963, WEISE 1963, WOLFSON 1959 a, b, 1960). There are, however, differences in the response to photoperiod in different species with different migratory habits. Furthermore, the endogenous control of onset, duration and termination of migration in some long-distance migrants has in the last decade become clear (B~RTHOLD et al. 1972, GWlNNER 1968 a, b, for review see GWlN- NER 1977 a).

In the Brambling, LoFts & MARSHALL (1960) found a clear photoperiodic effect on the onset of spring migration. Birds kept in short-day conditions showed no nocturnal restlessness during the natural migratory season, whereas birds kept in increasing daylength conditions did.

The birds in the present study have been exposed to an extremely variable photoperiod (between 4 and 19 hours daylength), very different from the natural photoperiodi- cal changes experienced by the flee-living conspecifics during the course of the migration and wintering. It is therefore not unlikely that the activity patterns of the experimental birds differ somewhat from the expected patterns of the free-living ones (e.g. termination of autumn migratory restlessness and onset of spring migratory restless- hess).

The late termination of the autumn migratory restlessness (c.f. Fig. 2 b) could be explained in two ways. First, the fast decreasing photoperiod before the winter solstice acts as a proximate force for continuing the migration. When daylengths increase again after the winter solstice, the birds expect themselves to be at the wintering grounds (with longer days than the breeding areas and the areas passed during the migration) and terminate the migratory restlessness. Secondly, the migratory restlessness might be internally controlled. In spite of the abnormal photoperiodic conditions to which the experimental birds are exposed, the termination (and onset) of migration is partly controlled by an innate migratory program which ensures the birds to reach their pro- per wintering grounds.

As pointed out by GWINNER (1968 a, b) and BERTHOLD et al. (1972), an endogenous time-program is most important for the control of migration in warblers (genera Pbyl- loscopus and Sylvia) and there is increasing evidence that this might be valid also for some short- and middle-distance migrants (BERTHOLD 1974, 1977). POHL (1971) demon-

70 P. LUNDBERG [J. Orn. [ 122

strated an endogenous circannual rhythmicity in body-weight and migratory restlessness in the Brambling, indicating that also in this less pi'onounced migratory species, the migration is more or less ruled by an innate program. This was also proposed by STOLT (1977 a) for the Yellowhammer Emberiza citrinella, a species with a migratory habit similar to the Brambling, at least in northern Europe. It is difficult to say which of the two explanations mentioned above is most valid. It is clear, however, that the inter- pretation is more dangerous when the birds are kept in nLD, than in photoperiodic neutral conditions (LD 12 : 12). In the latter conditions, the photoperiodic influence is ruled out and a possible endogenous rhythmicity will be more apparent. The late onset of spring migratory restlessness is perhaps more difficult to explain. After 22 March the, daylengths rapidly increase (especially in northern latitudes) and would possibly be a strong force for the onset of spring migration. LoFrs& MARSHALL (1960) also showed that increasing photoperiod in spring is an active stimulus for onset of migration in the Brambling. However, GWINNER (1977 b) and G~NSHIRT ~ GWINNER (1979) have shown that the actual photoperiod is not necessarily the critical stimulus, but also that photoperiodic conditions months back might have an important influence on the annual cycle, especially under extreme photoperiodic conditions.

The continuation of spring migratory restlessness in late spring and early summer is certainly another example of the so called "Sommerunruhe" (MERKEL 1956). The significance of that widespread habit among caged migrants is not yet fully clarified and is recently discussed by GWINNER ~ CZESCHLIK (1979).

It is evident, that even under the extraordinary photoperiodic conditions in northern latitudes, the migratory restlessness becomes well-developed and fairly well synchro- nized with the natural migratory season in caged Bramblings. The relationship between external and internal control of the migration in this species is however not fully known, and further investigation is therefore required.

Acknowledgements: I am indebted to Prof. K. MOLLER and Dr. L. O. ERIKSSON for valuable criticism on the manuscript and advice during the experimental work and to Mr. I. BERGLUND for constructive discussions.

Summary The migratory restlessness was studied in caged Bramblings in northern Sweden under natural

light conditions 17 September 1977 to 25 May 1978. The experimental birds showed a well-developed migratory restlessness during the natural migratory season of the free-living conspecifics. The migratory restlessness lasted longer than the natural migratory period in autumn, and the onset of migratory restlessness in spring was delayed compared with the natural migratory period. The discrepancies are probably due to the abnormal photoperiodic conditions to which the experimental birds were exposed. Different diurnal activity patterns during different times of the year reflect the migratory habit of the species, i.e. the Brambling is both a nocturnal and diurnal migrant. The quantity of the diurnal activity per hour was clearly positively correlated with the length of photoperiod. The photoperiodic and endogenous influence on the migration of the Brambling is discussed.

Heft 1 ] Migratory restlessness in Bramblings 71 1981 J

Zusammenfassung

Z u g u n r u h e bei gek~f ig ten Bergf inken in Nordschweden

Die Zugunruhe gek~figter Bergfinken wurde yore 17. Sept. 1977 bis 15. Mai 1978 unter natfir- lichen Lichtbedingungen in Nordschweden untersucht. W~.hrend der Zugperiode freilebender Bergfinken zeigten die gek~.figten Individuen deutliche Zugunruhe. Im Herbst dauerte die Periode der Zugunruhe l~.nger als die Zugperiode freilebender Bergfinken, im Frohjahr war das Einsetzen der Zugunruhe gegentiber dem nattirlichen Zugbeginn verz6gert. M6glicherweise waren diese Unterschiede eine Folge der abnormen photoperiodischen Bedingungen, unter denen die K~figv6gel lebten. Unterschiedliche Muster der Tagesaktivitst in den einzelnen Jahreszeiten deuten das Zugverhalten der Art an: Bergfinken sind sowohl Nacht- als auch Tagzieher. Die Menge der Tagesaktivit~it pro Stunde war deutlich positiv mit der L~.nge der Photoperiode korre- liert. Der photoperiodische und endogene Einflufl auf das Zugverhalten des Bergfinken wird dis- kutiert.

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Author's address: Dept. of Animal Ecology, University of Ume~i, S--90187 Ume~, Sweden.

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Migratory restlessness in caged BramblingsFringilla montifringilla in northern Sweden