Construction patterns of birds’ nests provide insight into ... › articles › 3010.pdf · during bending. For the nest walls, samples were taken from sides both parallel and perpendicular

Submitted 5 July 2016Accepted 21 January 2017Published 28 February 2017

Corresponding authorsLucia Biddle lbiddlelincolnacukD Charles Deemingcdeeminglincolnacuk

Academic editorLouise Barrett

Additional Information andDeclarations can be found onpage 15

DOI 107717peerj3010

Copyright2017 Biddle et al

Distributed underCreative Commons CC-BY 40

OPEN ACCESS

Construction patterns of birdsrsquo nestsprovide insight into nest-buildingbehavioursLucia Biddle Adrian M Goodman and D Charles DeemingSchool of Life Sciences Joseph Banks Laboratories University of Lincoln Lincoln United Kingdom

ABSTRACTPrevious studies have suggested that birds and mammals select materials needed fornest building based on their thermal or structural properties although the amountsor properties of the materials used have been recorded for only a very small numberof species Some of the behaviours underlying the construction of nests can beindirectly determined by careful deconstruction of the structure and measurementof the biomechanical properties of the materials used Here we examined this ideain an investigation of Bullfinch (Pyrrhula pyrrhula) nests as a model for open-nestingsongbird species that construct a lsquolsquotwigrsquorsquo nest and tested the hypothesis that materials indifferent parts of nests serve different functions The quantities of materials present inthe nest base sides and cup were recorded before structural analysis Structural analysisshowed that the base of the outer nests were composed of significantly thicker strongerand more rigid materials compared to the side walls which in turn were significantlythicker stronger and more rigid than materials used in the cup These results suggestthat the placement of particular materials in nests may not be random but furtherwork is required to determine if the final structure of a nest accurately reflects theconstruction process

Subjects Animal Behavior Bioengineering ZoologyKeywords Construction materials Structural properties Bullfinch

INTRODUCTIONNests built bymost birds are essential for reproductive success with considerable amountsof time and energy being spent by some species (Berg et al 2006) Although Collias ampCollias (1984) and Hansell (2000) provide general descriptions of avian nest constructionwe know relatively little detail for particular species (Healy Morgan amp Bailey 2015) and fewreports quantify the materials used in nests (Deeming amp Mainwaring 2015) The choicesof the materials within different parts of a nest presumably reflect decisions made by thebuilding bird and appear to have a structural role Recent studies have tried to determinethe factors that affect nest construction both using captive species and by examining nestsfrom the field Bailey et al (2014) showed that captive Zebra Finches (Taeniopygia guttata)select artificial nesting material (string) based on its structural properties and that theexperience of the bird influences their choice of materials Furthermore birds also showan apparent sensitivity to material length (Muth amp Healy 2014) A study on wild CommonBlackbirds (Turdus merula) showed that the birds appear to select thicker stronger more

How to cite this article Biddle et al (2017) Construction patterns of birdsrsquo nests provide insight into nest-building behaviours PeerJ5e3010 DOI 107717peerj3010

rigid materials for the outer nest wall compared to the cup lining or inner structural wall(Biddle Deeming amp Goodman 2015) There were also significant differences within the cupwall materials at the base of the cup were thicker stronger and more rigid than those fromthe top This suggests that these birds may have some level of awareness of where and whento place different materials in order to create a nest structure This has yet to be testedexperimentally and the mechanism behind this is unknown but captive Zebra Finches areable to learn to choose between nest materials on the basis of structural properties (Baileyet al 2014Muth Steele amp Healy 2013)

Other animals have also been shown to select materials in a non-random mannerduring construction of nests and other structures beavers (Castor fiber) predominantlyuse branches from willow (Salix) and poplars (Populus) in the construction of their lodgesirrespective of the availability of other species (Fustec amp Cormier 2007) Branch materialswere also selected on the basis of their thickness and where alder (Alnus) species were usedbeavers used thinner branches measuring 15ndash35 cm in diameter (Barnes amp Mallik 1996)Furthermore orang-utans have been shown to select materials based on their structuralproperties nests were constructed using weaker and more flexible branches for the liningand stronger more rigid and thicker ones for themain structure (Van Casteren et al 2012)

To date detailed descriptions of materials used in nest construction are limited toonly a few bird species and these tend to build nests either within cavities (eg BlueTits) or appear to have a more complex internal structure such as a mud cup within astructural nest wall (eg Common Blackbirds) This study furthers our understandingof the variability in nest construction for different passerine species by investigating thestructure and functional properties of Eurasian Bullfinch (Pyrrhula pyrrhula) nests Theseare superficially a cup of woven grasses located within a depression of outer nest materialmade of twigs (Bochenski amp Oles 1981) We hypothesised that the different structuralregions of Bullfinch nests would have different physical characteristics and that this wouldrelate to the materials they are composed of

METHODSNest characteristicsThirteen bullfinch nests were collected in September 2014 after the known end of thebreeding season Nests were collected by BTO nest recorders who very carefully removedthe nests from their location to ensure that the nests retained their structural integrity andcomposition All but one of the nests were collected from the Greater Manchester areain north-west England and the other nest was from Tyne and Wear north-east EnglandAlthough exact construction dates were unknown dates of clutch initiation were recordedand suggested that construction generally took place around the end of March to thebeginning of April The nests were well packaged in cardboard boxes during transportationto the University of Lincoln in order to reduce the chance of damage

In Lincoln each nest was dried before being placed in a plastic bag and stored in acardboard box at approximately room temperature and humidity In order to provide aconsistent base for comparison each nest was conditioned at 23 C 50 relative humidity

Biddle et al (2017) PeerJ DOI 107717peerj3010 217

in a Sanyo MLR-351H environmental chamber for 7ndash8 weeks until they had equilibratedto a constant weight All testing of materials was performed within 24 h after removal fromthe cabinet

The weight of each nest was measured using electronic scales (A amp D Company Limitedmodel FX-3000i) and the depth of nests and their width and length were measured usingdial callipers Overall the nests were elliptical in shape so the diameter of the cup and wallthickness were measured both parallel and perpendicular to the long axis of the cup Thevolume of the nest cupwasmeasured by lining the cupwith domestic cling film before fillingthe nest cup level to the top edge with 5 mm diameter solid-glass beads (SigmandashAldrich)which were weighed to allow calculation of volume based on a pre-determined density(Biddle Deeming amp Goodman 2015)

Nest deconstructionBefore deconstruction nests were visually examined to identify any distinct regions Themain easily identifiable regions identified were the outer nest which consisted of pieces ofplant material typically twigs which were loosely interwoven and the cup wall in generalconstructed of roots and grass culms tightly interwoven into a cup like shape (Fig 1) Fortwo nests a distinct lsquosecondaryrsquo cup was present between the cup and the outer materialthis was included as part of the cup and was not tested separately Variation in the verticalplane of the outer nest was investigated by separating the nests into a lower lsquobasalrsquo regiondefined as anything below the external base of the cup and an upper lsquotoprsquo region whichwere effectively the sides of the nest around the cup (Fig 1A) There was no obvious verticalvariation in the cup therefore it was analysed as a whole

Nests were carefully deconstructed by one person (LE Biddle) into their regions byseparating elements using forceps and taking care not to damage the materials The wallsof the outer nest were first removed until the lower limit of the outer part of the cup wasreached The cup was then removed to leave the base of the outer nest (Figs 1B and 1C)

In order to investigate variation in the morphology of the nest construction materialssix pieces of nest material were selected at random using a random number generatorfrom each region across all nests cup base and upper nest (from areas both parallel andperpendicular to the long axis) For each sample the length (mm) and if present the numberof lateral (side) branches were recorded In addition the degree of taper of the main axisof the sample was investigated by measuring the diameter using callipers at the widest endof the sample (base) and at base +2 cmmdashthe difference between the two values provided ameasure of the degree of taper (reduction in sample thickness)

Mechanical analysisMechanical analysis took place to determine if nests built by Bullfinches had a similararrangement in the structural components to those seen in nests of other species such asCommon Blackbirds (Biddle Deeming amp Goodman 2015) where the outer nest materialswere shown to be significantly thicker stronger andmore rigid that the cup liningmaterialsFurthermore it would allow comparisons with the structural properties of nests fromnon-avian species


Cup Outer Nest

Cup

Base

(a)

(b)

(c)

Figure 1 (A) Bullfinch nest deconstruction regions Grey Cup wall White Outer nest top BlackOuter nest base (B) A Bullfinch nest with the upper outer nest removed to reveal the cup in situ andbase of the nest (C) A Bullfinch nest deconstructed into the cup and outer nest components


After deconstruction all construction elements from the outer nest were arranged inorder of increasing size and the 20 thickest samples were selected from each vertical regionfor mechanical testing Only samples with a diameter greater than 03 mm were testedthinner samples were too small to reliably test because of the very low forces generatedduring bending For the nest walls samples were taken from sides both parallel andperpendicular to the main axis of the nest and for the base of the nest samples were takenirrespective of orientation The same sampling process was applied to materials within thecup but this was not separated into vertical regions For the cup the 20 thickest sampleswere selected

All samples were then subjected to three-point bending tests using an Instron universaltesting machine model 4443 fitted with a 100 N load cell (Biddle Deeming amp Goodman2015) Before testing the midpoint of the samples was measured using Mitutoyo digitalcallipers (Accuracy of plusmn002 mm) and the number of hollow samples were recorded Apushing probe of radius 5 mm was lowered until it just touched the sample placed on twosupports on either side A minimum span-to-depth ratio of 20 was used for each samplein order to limit the effects of shear (Vincent 1992) The crosshead was then automaticallylowered at a rate of 10 mm minminus1 causing the sample to bend until it eventually failed Aninterfaced computer produced a graph of force versus displacement allowing the structuralproperties of the beam to be calculated (Gordon 1978)

The bending rigidity (EI in Nm2 Eq (1)) of a uniform beam is the resistance of thatbeam to curvature where dF

dδ is the initial slope of the force displacement curve Bendingstrength or maximum bending moment (M in Nm) is given in Eq (2) where Fmax is themaximum force (N) a sample will withstand before it fails and L is the distance betweenthe supports in metres

EI = L3(dFdδ

)48 (1)

M = FmaxL4 (2)

Samples (50 64) that slipped from their supports during testing were excluded fromsubsequent analysis

Statistical analysisPaired t -tests showed there to be no significant difference in wall thicknesses between thedifferent orientations (parallel and perpendicular) in relation to the long axis of the nest(paired t -test t12 =minus034 p= 0741) so the values were pooled thereafter by taking amean value per nest prior to analysis Differences between the cup the outer nest and thelower and upper regions of the nest were investigated using a general linear mixed model(GLMM) in Minitab (version 17) controlling for nest identity as a random factor For nestcomposition each component present within the cup and the outer nest was expressed as aproportion before being arcsine transformed before analysis in order to normalise the dataand then running a stepwise discriminant analysis (Britt amp Deeming 2011) to compare thepercentage of each material within the cup and outer nest simultaneously using IBM SPSS


Statistics 21 The significance level for discrimination between the parts of the nest was setat an F-value of 384 (ie P lt 005) which is the default for the test General linear mixedmodelling was used to analyse the differences in the structural properties between the nestregions with nest identity as a random factor to control for the fact that samples from thesame nest were related (Biddle Deeming amp Goodman 2015)

RESULTSNest characteristics and compositionBullfinch nests were composed of an internal cup (internal volume 496 plusmn 131 cm3)that was physically distinct and easily detachable from the outer nest (Fig 1C) The cupwas asymmetrical with the long axis being approximately 22 longer than the shorterperpendicular axis (Table 1 paired t -test t12= 604 plt 0001) There was no significantdifference between the overall nest length perpendicular and parallel to the long axis of thecup (Table 1 paired t -test t12= 163 p= 013) The wall of the nest showed little variationin thickness between the base and upper wall of the nests (Table 1 paired t test t12= 0585p= 057)

The cup wall thickness was not significantly different at any of the four positionsmeasured around the nest (GLMM F348= 024 p= 0868) However the outer wall wasapproximately four times thicker than the wall of the cup and the cup depth was about halfof the nest height (Table 1)

The mean total nest mass was 147 g with the outer wall mass being significantly heavierthan the cup material (Table 1 paired t -test t12= 515 plt 0001) A significant differencewas also seen between the upper and basal regions of the outer wall with the base beingsignificantly heavier (paired t -test t12 =minus748 plt 0001) In the outer nest there wasno significant difference in the distribution of materials relative to the long axis (Table1 paired t -test t12=minus1017 p= 0329) The mass of the outer nest showed the greatestvariation between nests (coefficient of variation = 46) compared to the cup (coefficientof variation = 38)

The type of materials used varied between regions of the nests The cup was composedof finer lighter coloured material which was usually grass culms roots or thin twigs (Fig2A) visually this structure seemed more tightly woven than the outer nest The interior ofthe cup was not usually lined with animal-derived materials although some hair or fur wasfound within the material of the cup in around half the nests

The outer material of the nest was not as tightly packed as the cup becoming moreloosely bound at its extremities It was mainly composed of eudicotyledonous shoots eitherfrom trees (twigs) or from herbaceous species (eudicot herbs) roots and grass culms werealso present albeit only in small amounts (Fig 2A) When nests were composed of largenumbers of herbaceous eudicot shoots the individual elements tended to be shorter andmore highly branched than woody twigs and so gave an appearance of being more tightlywoven Longer woody elements tended to be located towards the base of the nest andin a few cases these woody elements were placed below the cup and incorporated withinthe herbaceous material Relatively few pieces of moss leaf artificial material and bark


Table 1 Mean (plusmnSD) values for structural dimensions of thirteen Bullfinch nestsWall thickness is theaverage of all 4 sides measured

Variable Meanplusmn SD Coefficient ofvariation ()

Nest diameter parallel to long axis (mm) 1310plusmn 256 20Nest diameter perpendicular to long axis (mm) 1184plusmn 207 18Ratio of nest diameters 11plusmn 02 18Cup diameter parallel to long axis (mm) 822plusmn 123 15Cup diameter perpendicular to long axis (mm) 673plusmn 76 11Ratio of cup diameters 12plusmn 13 108Outer wall thickness (mm) (calculated) 221plusmn 93 42Cup wall thickness (mm) 62plusmn 16 26Total upper wall thickness (mm) (calculated) 246plusmn 107 44Base wall thickness (outer nest and cup wall at base) (mm)(calculated)

264plusmn 111 42

Nest height (mm) 497plusmn 114 23Maximum cup depth (mm) 233plusmn 45 19Total nest mass (g) 147plusmn 50 34Outer wall base mass (g) 103plusmn 48 47Outer wall top mass (g) 12plusmn 07 58Outer wall top mass parallel to long axis (g) 05plusmn 04 80Outer wall top mass perpendicular to long axis (g) 06plusmn 03 50Total outer wall mass (g) 115plusmn 53 46Cup wall mass (g) 32plusmn 12 38Cup volume (cm3) 496plusmn 131 26

were found in the nests A few nests contained leaves and bark as well as human-derivedmaterials such as plastic and thread (Fig 2A) All nests contained an appreciable amount ofdust (Fig 2A) Discriminant analysis showed that the percentage of roots (Wilkrsquos λ= 024F124= 7655) grass culms (λ= 020 F223= 4566) and hair (λ= 167 F322= 3662) weresignificantly (plt 005) higher in the cup than the outer nest (Fig 2B)

Mechanical properties of the construction materialsThere were significant regional differences in the mechanical properties of the materialsused in the construction of Bullfinch nests In the outer nest the base region was composedof significantly thicker stronger andmore rigidmaterials than those from the upper regionsof the outer nest (Fig 3 Table 2) Furthermore samples from the base of the outer nestwere significantly less tapered and had more longer lateral branches compared to thosefrom the upper region of the outer nest (Tables 2 and 3)

There were significant differences between the materials from the upper part of the outernest and the cup Samples from the upper outer nest were significantly thicker strongerand more rigid than those from the cup (Fig 3 Table 2) Significantly more taperedelements were in the upper outer nest material compared to the material found within thecup (Tables 2 and 3) Sample length and number of lateral branches were similar to the


0

2

4

6

8

10

12

Eu

dico

t twigs

Eu

dico

t herb

aceo

us sh

oo

ts

Grass

Ro

ots

Mo

ss

Ha

ir

Du

st

Leaves

Plastic

Ba

rk

Th

read

Am

ou

nt

of

mat

eri

als

wit

hin

eac

h r

egi

on

(g)

Nest Composition

Total

Outer Nest

Cup

(a)

0

10

20

30

40

50

60

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90

Eu

dico

t twigs

Eu

dico

t herb

aceo

us sh

oo

ts

Grass

Ro

ots

Mo

ss

Ha

ir

Du

st

Leaves

Plastic

Ba

rk

Th

read

Am

ou

nt

of

mat

eri

al w

ith

in e

ach

re

gio

n (

)

Nest Component

Outer Nest

Cup

(b)

Figure 2 Within-nest variation in the composition of Bullfinch nests the nests were separated into theouter nest and cup region along with the overall nest expressed as (A) mass and (B) percentage of thedifferent componentsValues are means+1 standard deviation


outer nest walls (Tables 2 and 3) There were no significant differences in the percentageof hollow samples between the regions (Tables 2 and 3)

DISCUSSIONBullfinches build nests predominately out of twigs and line their nest cups with finer morepliable plant materials rather than animal-derived materials Our analysis of the structuralproperties of the materials showed that the bases of the outer nests were composed ofsignificantly thicker stronger and more rigid materials than the side walls which in turnwere significantly thicker stronger and more rigid than materials used in the cup

Nest dimensions and constructionBullfinch nests are predominately constructed by the female bird (Ferguson-Lees Castellamp Leech 2011) The nest dimensions recorded here are comparable to those previouslydescribed (Bochenski amp Oles 1981) although the total weight of the nest and the cup wereslightly lower than previously reported (Doerbeck 1963) The difference in weight mayreflect differences in year of collection andor difference in location as seen in otherpasserine species (Britt amp Deeming 2011 Crossman Rohwer amp Martin 2011 Deeminget al 2012 Mainwaring et al 2012 Mainwaring et al 2014) The cup was elliptical aspreviously reported in Bullfinch (Bochenski amp Oles 1981) and Common Blackbird nests(Biddle Deeming amp Goodman 2015) which presumably reflects the shape of the birdrsquosprofile as it sits within its nest Elliptical nest shapes have also been reported in non-avianspecies Orang-utans also construct asymmetrical nests where the long axis of the nest isorientated toward the trunk of the supporting tree (Van Casteren et al 2012) It wouldbe interesting to investigate whether birds also orientate their nests in situ in line withsupporting structures to more effectively distribute the load Such studies would providefurther insight into the selection of nest location in relation to the architecture of supportingstructures

The materials the Bullfinches used during nest construction were similar to thoserecorded previously (Nicolai 1956 Newton 1978 Bochenski amp Oles 1981) However onlytwo of the nests analysedwere linedwith hair which contradicts the report that suggests thatall nests are lined with hair (Ferguson-Lees Castell amp Leech 2011) Other reports make noreference to hair (Nicolai 1956) although a nest composed of only hair has been observed(Doerbeck 1963) A significant difference was seen in Bullfinch nests between the materialsused in the outer nest and the cup with respect to their insulatory properties (Hilton etal 2004) based on mass there was considerably more hair and dry grass in the cup Sucha distribution suggests that during construction the birds were selecting materials withparticular characteristics for different parts of the nest

Structural properties of nest materialsThe separation of the nest into an outer region and cup is supported by Bochenski amp Oles(1981) work on Bullfinch nests which showed that the cup was built in a depression withinthe outer nest material For the first time we are able to demonstrate that there weresignificant differences in the structural properties of the various materials used to construct


0

05

1

15

2

Top Base Cup

Dia

me

ter

(mm

)Sample Location

(a)

0

5

10

15

20

25

30

Top Base Cup

Be

nd

ing

Stre

ngt

h

(Nm

x 1

0-3

)

Sample Location

(b)

0

500

1000

1500

2000

2500

Top Base Cup

Rig

idit

y (N

msup2

x 1

0-6

)

Sample Location

(c)

Figure 3 Variation in the (A) diameter (B) strength and (C) rigidity of the different nest regions forthe 13 nestsValues are means+1 standard deviation

a Bullfinch nest depending on location within the structure as whole The positioningof the various materials into different parts of the nest appears to be non-random Thematerials in the top of the outer nest were approximately 59 thicker 474 stronger and810 more rigid than the materials used in the cup This may be to provide a supportingframework for the cup and incubating bird whereas the cup is constructed of more flexiblematerials providing better direct support for the eggs and nestlings

There were also significant differences in the properties of construction materials in thevertical profile of the outer nest the material at the base was 59 thicker 224 strongerand 323 more rigid than the material found in the upper nest surrounding the cup Thenon-random distribution of different materials suggests that the birds are therefore ableto distinguish between nest construction materials and place the stronger and more rigidones in the base which is presumably built first and so supports side walls and the cupfrom below Bullfinches are reported to place the cup on top of the outer nest materialbut not all of the outer nest material is placed below the base of the cup (Bochenski ampOles 1981) This contrasts with the study of Common Blackbird nests which showed nosignificant vertical difference in the mechanical properties of construction materials inthe outer nest materials but did show that at least in the cup lining there were stronger


Table 2 Results of general linear mixedmodelling to test the effect of location within the nest for various structural measures controlling for nest as a random factorin the modelMaterials in the outer nest are compared with those from the upper wall and the base (Fig 2) The materials from the upper nest wall are also compared tothe cup materials (Fig 2) Values are exponents for changes relative to the characteristics of the upper part of the nest together with accompanying F-values with the de-grees of freedom (df ) shown in the row and p-values in parentheses also includes the exponent and standard error (SE)

Vertical (outer nest upper vs base) Wall region (upper outer nest vs cup)

Variable Change in baserelative to upper(exponentplusmn SE)

Location (F112) Nest (F1212) Change in cuprelative to upper(exponentplusmn SE)

Location (F112) Nest (F1212)

Diameter 0291plusmn 0026 12499 (lt0001) 424 (0009) minus0184plusmn 0028 4362 (lt0001) 265 (0052)Bending strength 0007plusmn 0001 5278 (lt0001) 270 (0049) minus0002plusmn 0001 1438 (0003) 111 (0431)Rigidity 5555plusmn 764 5290 (lt0001) 412 (0010) minus1530plusmn 566 730 (0019) 106 (0460)Length of branches 59plusmn 25 569 (0034) 169 (0188) minus527plusmn 247 456 (0054) 159 (0218)Taper minus0044plusmn 0015 882 (0012) 177 (0169) minus0073plusmn 0016 2095 (0001) 085 (0605)Number of lateralbranches

0481plusmn 0140 1174 (0005) 450 (0007) 0168plusmn 0289 034 (0572) 042 (0928)

Hollow samples () 0223plusmn 0275 066 (0433) 222 (0090) minus0327plusmn 0349 088 (0367) 058 (0818)

Biddle

etal(2017)PeerJDO

I107717peerj30101117

Table 3 Mean (plusmnSD) values for the physical properties of the samples of nest materials taken from thedifferent parts of the nest Sample sizes length of branches and number of lateral branches (mean nmdashtop(118) base (6) Cup (6)) Taper (mean nmdashtop (117) base (6) Cup (6)) percentage of hollow samples(mean nmdashtop (166) base (20) Cup (186))

Position in nest

Variable Top Base Cup

Construction element length (mm) 7248plusmn 1206 8427plusmn 1680 6195plusmn 1623Taper of construction elements (mm) 020plusmn 009 011plusmn 008 006plusmn 006Number of lateral branches 147plusmn 102 244plusmn 133 181plusmn 142Hollow samples () 206plusmn 185 346plusmn 356 82plusmn 75

and more rigid materials at the base of the cup itself (Biddle Deeming amp Goodman 2015)Captive male Zebra Finches learn to base material choice on structural properties choosingstiffer rather than more flexible string samples to build their nests (Bailey et al 2014) Itwas also found that during the building process of the nest the stiffer material appearedto be the most effective material compared to more flexible material with fewer piecesrequired (Bailey et al 2014) The non-random placement of materials apparently based ontheir mechanical properties suggests that during nest construction Bullfinches CommonBlackbirds and captive Zebra Finches are able to choose materials However laboratorybased studies where birds are provided with limited types of nest materials with relativelysimilar properties do not necessarily reflect the natural environment and it would beinteresting to investigate what choices Zebra Finches would make if they were providedwith more natural nesting materials

There were also significant differences in the thickness degree of branching and taperof the construction elements used within Bullfinch nests (Table 2) Again the distributionof these materials was not random The base of the nest was composed of thicker longerand less tapered elements these could provide the main supporting members during theearly construction of the nest but also help the base of the nest to support the birds eggsand rest of the nest structure Basal elements also exhibited a higher number of lateral(side) branches which may have helped to keep the structure together it was noted thatthese side branches were often interwoven presumably by the birds when building thenests to the main nest structure The upper region of the outer nest had significantly moretapered (greater reduction in sample thickness) elements compared to those in the cup Theincreased taper may allow the birds to weave the materials together more easily Whetherthis pattern is repeated in other species that construct nests primarily out of twigs egthe Hawfinch (Coccothraustes coccothraustes Ferguson-Lees Castell amp Leech 2011) requiresfurther investigation

Comparison of the mechanical values obtained for Bullfinches with those of CommonBlackbirds (Biddle Deeming amp Goodman 2015) shows that the outer nest materials usedin the construction of Bullfinch nests were similar in thickness strength and rigidity Thisis despite the fact that Bullfinches are around a third of the mass of Common Blackbirds(Cramp 1988 Cramp amp Perrins 1994) These differences may reflect the lack of a mudcup in Bullfinch nests where the outer nest supports the parent as well as eggsnestlings


In Common Blackbirds nests the mud cup is an additional structural element althoughit is likely to significantly contribute to the nestrsquos self-weight and therefore the nests havethicker support elements to allow for this There were differences in the composition of thecups between the two species Common Blackbird nests were lined with dry grass but thiswas not woven into any structure (Mainwaring et al 2014 Biddle Deeming amp Goodman2015) By contrast the elements used in the cup of Bullfinches were generally thinnerweaker and more flexible but were woven to form a discrete structure These differencesmay also reflect the lack of the mud cup or the smaller body size of the Bullfinch Thenests were studied ex situ and structural differences may reflect the support provided bythe underlying structuresmdashCommon Blackbirds often build nests in forks of trees whereasBullfinches prefer sites such as a tangle of twigs (Ferguson-Lees Castell amp Leech 2011)which offer less support from below

A description of nest construction behaviour is unavailable for Bullfinches and so weare unable to categorically state that the birds are selecting the materials that they placein different parts of the nest However the differing physical and structural properties ofthese materials imply that the process of nest construction involves a non-random patternof behaviour in the placement of various materials as construction of the nest progressesGiven that the amounts of materials used in each region of the nest is typically less than10 g we can safely assume that the materials that Bullfinches could use and do use innest construction will be in massive excess in their environment and so their behaviouris unlikely to be limited by material availability It would be fascinating to test whethercaptive Bullfinches exhibit any selection of particular nest materials to fit the pattern ofusage predicted from the data derived from wild birds

Further investigations of nest construction in these and other passerine species shouldinvestigate whether it is important to relate the size of the clutch and weight of the nestlingsand parent to the structural properties of the nest Moreover further work is requiredto investigate the structural properties of nest materials from a greater range of speciesof different body sizes and nesting locations to help better understand the factors thatdetermine choice of nest material (Deeming amp Mainwaring 2015) For instance do largerheavier bird species with large clutches build nests with thicker twigs in the base of the nestthan smaller species with small clutches

Nest construction materials and nest building behaviourWe believe that this study and that of Biddle Deeming amp Goodman (2015) provides insightinto the non-random nature of nest construction behaviour of the species concerned Ourresults suggest that Bullfinches might first construct a strong platform to support the nestThey then change the criteria that they use to choose materials for building the side wallsof the nest Finally the cup is built using a differing arrangement of yet another typeof material Hence we believe that nest morphology in bullfinches reflects at least threedifferent phases of construction behaviour though we acknowledge that this has not beentested experimentally We feel that a tri-phasic but different pattern of construction isalso evident in Common Blackbirds the first phase of nest construction provides a strongbase and surrounding layer prior to the preparation of the mud cup Finally this cup is


lined with dry grasses (Biddle Deeming amp Goodman 2015) We appreciate that evidence isindirect but experiments have shown that when captive zebra finches are provided with achoice of nest materials they actively select specific materials for nest buildingMuth Steeleamp Healy (2013) showed that zebra finches preferred a colour for nesting material but didnot prefer a colour for food this suggests that it is not just colour that determines thebehaviour Another study showed that zebra finches selected the lengths of nest materialsto match the size of an entrance hole to a nest box but also changed their behaviour asnest-building proceeds as their experience increased (Muth amp Healy 2014) Such studiessuggest that during nest construction the birds are deciding upon nest materials of differingproperties It is possible that if captive birds exhibit such discriminatory behaviour wildbirds could also behave in a similar way in a natural environment Wemake no claim aboutthe cognitive abilities of the birds to achieve this process but rather point out that use ofdifferent materials in various parts of the nest potentially indicates a change in behaviouras each part is constructed

However it could be argued that the finished nest provides little insight into itsconstruction Birds may bring differing types of materials to the nest in a random mannerand only those that are appropriate to that particular location for instance perhapsstronger elements in the base simply remain in place as nest construction continuesother inappropriate materials are somehow lost However if this were the case one wouldanticipate that as the nest grew in size and complexity materials would be retained by thebulk of the structure In particular thick strong twigs more typically associated with thenest base should be equally distributed throughout the nest and would be found in thecup It would be predicted that the distribution of materials in the finished structure wouldbe random but we clearly demonstrate that the location of materials is non-random inboth Bullfinch and Common Blackbird nests In additionHowell (1943) describes how theAmerican Robin (Turdus migratorius) which is closely related to the Common Blackbirdchanges its behaviour as nest construction proceeds by bringing in different materials atprogressive stages

We accept that our interpretation of nest morphology reflecting nest constructionbehaviour is circumstantial and requires further work However our data allow us topostulate a hypothesis that bullfinches are able to distinguish between materials basedphysical properties and will be selective in their use during nest construction It would befascinating to test this hypothesis using captive birds that are offered materials of knownphysical properties during nest construction We would predict that the birds would selectdifferent materials during the various phases of nest-building Alternatively we could applyour methods to bullfinch nests abandoned at different stages of construction where wewould anticipate that a nest abandoned when only the base had been constructed wouldhave similar materials to what we observed in completed nests Although it was not possiblein this study our results do suggest that a study of the behaviour used by a bird to constructa nest which is then linked to the subsequent deconstruction of that nest should be apriority area of further research

To conclude our understanding of nest construction behaviour in birds is very poorTo date there are still relatively few detailed descriptions of nest construction behaviour


(Healy Morgan amp Bailey 2015) and despite novel and revealing behavioural studies usingcaptive Zebra Finches building with artificial materials (Muth Steele amp Healy 2013 Baileyet al 2014 Bailey et al 2015 Muth amp Healy 2014) relatively little is known about nestconstruction in the natural environment We feel that careful deconstruction of nestscollected from the wild when linked with studies into the structural properties of thematerials offers an indirect but valuable insight into nest construction behaviour not onlyin birds (Biddle Deeming amp Goodman 2015) but also in mammals (Van Casteren et al2012) Future research is needed to record nest construction behaviour in greater detailwhilst quantifying the materials used in a wide range of species with varying nest typesMoreover there should be greater consideration of the location of nests in situ whichwill help us develop a broader understanding of factors eg nest site affecting how nestsinteract with their natural environment

ACKNOWLEDGEMENTSMany thanks go to Wayne Parry and Richard Winship who supplied the nests used inthis study Many thanks also go to Carl Barrimore and Dave Leech of the British Trustfor Ornithology Nest Record Scheme for their assistance in publicising our need for birdnests We are grateful to Tom Pike for statistical advice and to Fred Rumsey for help withidentification of a plant species commonly found in the nests

ADDITIONAL INFORMATION AND DECLARATIONS

FundingStudentship was funded by the University of Lincoln The funders had no role in studydesign data collection and analysis decision to publish or preparation of the manuscript

Grant DisclosuresThe following grant information was disclosed by the authorsUniversity of Lincoln

Competing InterestsThe authors declare there are no competing interests

Author Contributionsbull Lucia Biddle conceived and designed the experiments performed the experimentsanalyzed the data wrote the paper prepared figures andor tables reviewed drafts of thepaperbull Adrian M Goodman conceived and designed the experiments analyzed the datacontributed reagentsmaterialsanalysis tools wrote the paper reviewed drafts of thepaperbull D Charles Deeming conceived and designed the experiments analyzed the data wrotethe paper reviewed drafts of the paper


Data AvailabilityThe following information was supplied regarding data availability

The raw data has been supplied as a Data S1

Supplemental InformationSupplemental information for this article can be found online at httpdxdoiorg107717peerj3010supplemental-information

REFERENCESBailey IE Morgan KV Bertin M Meddle SL Healy SD 2014 Physical cognition birds

learn the structural efficacy of nest material Proceedings of the Royal Society BBiological Sciences 28120133225 DOI 101098rspb20133225

Bailey IE Muth F Morgan KV Meddle SL Healy SD 2015 Birds build camouflagednests Auk 13211ndash15 DOI 101642AUK-14-771

Barnes DMMallik AU 1996 Use of woody plants in construction of beaverdams in northern Ontario Canadian Journal of Zoology 74(9)1782ndash1786DOI 101139z96-197

BergML Beintema NHWelbergen JA Komdeur J 2006 The functional significanceof multiple nest-building in the Australian Reed Warbler Acrocephalus australis Ibis148(3)395ndash404 DOI 101111j1474-919X200600482x

Biddle LE Deeming DC Goodman AM 2015Morphology and biomechanics ofthe nest of the Common Blackbird Turdus merula Bird Study 62(1)87ndash95DOI 101080000636572014988119

Bochenski Z Oles T 1981 Experimental studies on the nesting of bullfinch Pyrrhulapyrrhula (Linnaeus 1758) in aviaries Acta Zoologica Cracoviensia 253ndash12

Britt J Deeming DC 2011 First-egg date and air temperature affect nest construc-tion in Blue Tit Cyanistes caeruleus but not in Great Tit Parus major Bird Study58(1)78ndash89 DOI 101080000636572010524916

Collias NE Collias EC 1984Nest building and bird behaviour Princeton PrincetonUniversity Press

Cramp S 1988Handbook of the birds of Europe the Middle East and North Africa thebirds of the Western Palearctic vol V tyrant flycatchers to thrushes Oxford OxfordUniversity Press

Cramp S Perrins CM 1994Handbook of the birds of Europe the Middle East and NorthAfrica the birds of the Western Palearctic vol VIII crows to finches Oxford OxfordUniversity Press

Crossman CA Rohwer VG Martin PR 2011 Variation in the structure of bird nestsbetween northern Manitoba and south eastern Ontario PLOS ONE 6(4)e19086DOI 101371journalpone0019086

Deeming DC MainwaringMC 2015 Functional properties of nests In Deeming DCReynolds SJ eds Nests eggs and incubation new ideas about avian reproductionOxford Oxford University Press


Deeming DC MainwaringMC Hartley IR Reynolds SJ 2012 Local temperatureand not latitude determines the design of Blue tit and great tit nests Avian BiologyResearch 5(4)203ndash208 DOI 103184175815512X13528874959581

Doerbeck F 1963 Zur Biologie der Gimpels Pyrrhula pyrrhula in der Grossstadt DieVogelwelt 8497ndash114

Ferguson-Lees J Castell R Leech D 2011 A field guide to monitoring nests ThetfordBritish Trust for Ornithology

Fustec J Cormier JP 2007 Utilisation of woody plants for lodge construction byEuropean beaver (Castor fiber) in the Loire valley FranceMammalia 7111ndash15DOI 101515MAMM2007002

Gordon JE 1978 Structures or why things donrsquot fall down London Penguin BooksHansell MH 2000 Bird nests and construction behaviour Cambridge Cambridge

University PressHealy SD Morgan KV Bailey IE 2015 Nest-construction behaviour In Deeming

DC Reynolds SJ eds Nests eggs and incubation new ideas about avian reproductionOxford Oxford University Press 16ndash28

Hilton GM Hansell MH Ruxton GD Reid JM Monaghan P 2004 Using artificial neststo test importance of nesting material and nest shelter for incubation energetics Auk121(3)777ndash787 DOI 1016420004-8038(2004)121[0777UANTTI]20CO2

Howell JC 1943 Notes on the nesting habits of the American robin (Turdus migratoriusL) American Midland Naturalist 28(3)529ndash603 DOI 1023072420891

MainwaringMC Deeming DC Jones CI Hartley IR 2014 Adaptive latitudinalvariation in Common Blackbird Turdus merula nest characteristics Ecology andEvolution 4841ndash851 DOI 101002ece3992

MainwaringMC Hartley IR Bearhop S Brulez K Du Feu CR Murphy G Plummer KWebber SL Reynolds SJ Deeming DC 2012 Latitudinal variation in blue and greattit nest characteristics indicates environmental adjustment Journal of Biogeography39(9)1669ndash1677 DOI 101111j1365-2699201202724x

Muth F Healy SD 2014 Zebra finches select nest material appropriate for a buildingtask Animal Behaviour 90237ndash244 DOI 101016janbehav201402008

Muth F Steele M Healy SD 2013 Colour preferences in nest-building zebra finchesBehavioral Processes 99106ndash111 DOI 101016jbeproc201307002

Newton I 1978 Finches London CollinsNicolai J 1956 Zur Biologie und Ethologie des Gimpels (Pyrrhula pyrrhula L) Ethology

13(1)93ndash132 DOI 101111j1439-03101956tb01549xVan Casteren A SellersWI Thorpe SS Coward S Crompton RHMyatt JP Ennos AR

2012 Nest-building orang-utans demonstrate engineering know-how to producesafe comfortable beds Proceedings of the National Academy of Sciences of the UnitedStates of America 109(18)6873ndash6877 DOI 101073pnas1200902109

Vincent JVF 1992 Biomechanics-materials a practical approach Oxford 165-IRL Pressat Oxford University Press


rigid materials for the outer nest wall compared to the cup lining or inner structural wall(Biddle Deeming amp Goodman 2015) There were also significant differences within the cupwall materials at the base of the cup were thicker stronger and more rigid than those fromthe top This suggests that these birds may have some level of awareness of where and whento place different materials in order to create a nest structure This has yet to be testedexperimentally and the mechanism behind this is unknown but captive Zebra Finches areable to learn to choose between nest materials on the basis of structural properties (Baileyet al 2014Muth Steele amp Healy 2013)

Other animals have also been shown to select materials in a non-random mannerduring construction of nests and other structures beavers (Castor fiber) predominantlyuse branches from willow (Salix) and poplars (Populus) in the construction of their lodgesirrespective of the availability of other species (Fustec amp Cormier 2007) Branch materialswere also selected on the basis of their thickness and where alder (Alnus) species were usedbeavers used thinner branches measuring 15ndash35 cm in diameter (Barnes amp Mallik 1996)Furthermore orang-utans have been shown to select materials based on their structuralproperties nests were constructed using weaker and more flexible branches for the liningand stronger more rigid and thicker ones for themain structure (Van Casteren et al 2012)

To date detailed descriptions of materials used in nest construction are limited toonly a few bird species and these tend to build nests either within cavities (eg BlueTits) or appear to have a more complex internal structure such as a mud cup within astructural nest wall (eg Common Blackbirds) This study furthers our understandingof the variability in nest construction for different passerine species by investigating thestructure and functional properties of Eurasian Bullfinch (Pyrrhula pyrrhula) nests Theseare superficially a cup of woven grasses located within a depression of outer nest materialmade of twigs (Bochenski amp Oles 1981) We hypothesised that the different structuralregions of Bullfinch nests would have different physical characteristics and that this wouldrelate to the materials they are composed of

METHODSNest characteristicsThirteen bullfinch nests were collected in September 2014 after the known end of thebreeding season Nests were collected by BTO nest recorders who very carefully removedthe nests from their location to ensure that the nests retained their structural integrity andcomposition All but one of the nests were collected from the Greater Manchester areain north-west England and the other nest was from Tyne and Wear north-east EnglandAlthough exact construction dates were unknown dates of clutch initiation were recordedand suggested that construction generally took place around the end of March to thebeginning of April The nests were well packaged in cardboard boxes during transportationto the University of Lincoln in order to reduce the chance of damage

In Lincoln each nest was dried before being placed in a plastic bag and stored in acardboard box at approximately room temperature and humidity In order to provide aconsistent base for comparison each nest was conditioned at 23 C 50 relative humidity









Cup Outer Nest

Cup

Base

(a)

(b)

(c)







EI = L3(dFdδ

)48 (1)

M = FmaxL4 (2)














264plusmn 111 42






0

2

4

6

8

10

12

Eu

dico

t twigs

Eu

dico

t herb

aceo

us sh

oo

ts

Grass

Ro

ots

Mo

ss

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ir

Du

st

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Plastic

Ba

rk

Th

read

Am

ou

nt

of

mat

eri

als

wit

hin

eac

h r

egi

on

(g)

Nest Composition

Total

Outer Nest

Cup

(a)

0

10

20

30

40

50

60

70

80

90

Eu

dico

t twigs

Eu

dico

t herb

aceo

us sh

oo

ts

Grass

Ro

ots

Mo

ss

Ha

ir

Du

st

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Plastic

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rk

Th

read

Am

ou

nt

of

mat

eri

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ith

in e

ach

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gio

n (

)

Nest Component

Outer Nest

Cup

(b)









0

05

1

15

2

Top Base Cup

Dia

me

ter

(mm

)Sample Location

(a)

0

5

10

15

20

25

30

Top Base Cup

Be

nd

ing

Stre

ngt

h

(Nm

x 1

0-3

)

Sample Location

(b)

0

500

1000

1500

2000

2500

Top Base Cup

Rig

idit

y (N

msup2

x 1

0-6

)

Sample Location

(c)











0481plusmn 0140 1174 (0005) 450 (0007) 0168plusmn 0289 034 (0572) 042 (0928)


Biddle

etal(2017)PeerJDO

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Position in nest



































































Cup Outer Nest

Cup

Base

(a)

(b)

(c)







EI = L3(dFdδ

)48 (1)

M = FmaxL4 (2)














264plusmn 111 42






0

2

4

6

8

10

12

Eu

dico

t twigs

Eu

dico

t herb

aceo

us sh

oo

ts

Grass

Ro

ots

Mo

ss

Ha

ir

Du

st

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Plastic

Ba

rk

Th

read

Am

ou

nt

of

mat

eri

als

wit

hin

eac

h r

egi

on

(g)

Nest Composition

Total

Outer Nest

Cup

(a)

0

10

20

30

40

50

60

70

80

90

Eu

dico

t twigs

Eu

dico

t herb

aceo

us sh

oo

ts

Grass

Ro

ots

Mo

ss

Ha

ir

Du

st

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Plastic

Ba

rk

Th

read

Am

ou

nt

of

mat

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ith

in e

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re

gio

n (

)

Nest Component

Outer Nest

Cup

(b)









0

05

1

15

2

Top Base Cup

Dia

me

ter

(mm

)Sample Location

(a)

0

5

10

15

20

25

30

Top Base Cup

Be

nd

ing

Stre

ngt

h

(Nm

x 1

0-3

)

Sample Location

(b)

0

500

1000

1500

2000

2500

Top Base Cup

Rig

idit

y (N

msup2

x 1

0-6

)

Sample Location

(c)











0481plusmn 0140 1174 (0005) 450 (0007) 0168plusmn 0289 034 (0572) 042 (0928)


Biddle

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Position in nest




























































Cup Outer Nest

Cup

Base

(a)

(b)

(c)







EI = L3(dFdδ

)48 (1)

M = FmaxL4 (2)














264plusmn 111 42






0

2

4

6

8

10

12

Eu

dico

t twigs

Eu

dico

t herb

aceo

us sh

oo

ts

Grass

Ro

ots

Mo

ss

Ha

ir

Du

st

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Plastic

Ba

rk

Th

read

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ou

nt

of

mat

eri

als

wit

hin

eac

h r

egi

on

(g)

Nest Composition

Total

Outer Nest

Cup

(a)

0

10

20

30

40

50

60

70

80

90

Eu

dico

t twigs

Eu

dico

t herb

aceo

us sh

oo

ts

Grass

Ro

ots

Mo

ss

Ha

ir

Du

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Plastic

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rk

Th

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in e

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n (

)

Nest Component

Outer Nest

Cup

(b)









0

05

1

15

2

Top Base Cup

Dia

me

ter

(mm

)Sample Location

(a)

0

5

10

15

20

25

30

Top Base Cup

Be

nd

ing

Stre

ngt

h

(Nm

x 1

0-3

)

Sample Location

(b)

0

500

1000

1500

2000

2500

Top Base Cup

Rig

idit

y (N

msup2

x 1

0-6

)

Sample Location

(c)











0481plusmn 0140 1174 (0005) 450 (0007) 0168plusmn 0289 034 (0572) 042 (0928)


Biddle

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EI = L3(dFdδ

)48 (1)

M = FmaxL4 (2)














264plusmn 111 42






0

2

4

6

8

10

12

Eu

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t twigs

Eu

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ots

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st

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Plastic

Ba

rk

Th

read

Am

ou

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wit

hin

eac

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egi

on

(g)

Nest Composition

Total

Outer Nest

Cup

(a)

0

10

20

30

40

50

60

70

80

90

Eu

dico

t twigs

Eu

dico

t herb

aceo

us sh

oo

ts

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Ro

ots

Mo

ss

Ha

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Plastic

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in e

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n (

)

Nest Component

Outer Nest

Cup

(b)









0

05

1

15

2

Top Base Cup

Dia

me

ter

(mm

)Sample Location

(a)

0

5

10

15

20

25

30

Top Base Cup

Be

nd

ing

Stre

ngt

h

(Nm

x 1

0-3

)

Sample Location

(b)

0

500

1000

1500

2000

2500

Top Base Cup

Rig

idit

y (N

msup2

x 1

0-6

)

Sample Location

(c)











0481plusmn 0140 1174 (0005) 450 (0007) 0168plusmn 0289 034 (0572) 042 (0928)


Biddle

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0

2

4

6

8

10

12

Eu

dico

t twigs

Eu

dico

t herb

aceo

us sh

oo

ts

Grass

Ro

ots

Mo

ss

Ha

ir

Du

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Plastic

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rk

Th

read

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ou

nt

of

mat

eri

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wit

hin

eac

h r

egi

on

(g)

Nest Composition

Total

Outer Nest

Cup

(a)

0

10

20

30

40

50

60

70

80

90

Eu

dico

t twigs

Eu

dico

t herb

aceo

us sh

oo

ts

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Ro

ots

Mo

ss

Ha

ir

Du

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Plastic

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n (

)

Nest Component

Outer Nest

Cup

(b)









0

05

1

15

2

Top Base Cup

Dia

me

ter

(mm

)Sample Location

(a)

0

5

10

15

20

25

30

Top Base Cup

Be

nd

ing

Stre

ngt

h

(Nm

x 1

0-3

)

Sample Location

(b)

0

500

1000

1500

2000

2500

Top Base Cup

Rig

idit

y (N

msup2

x 1

0-6

)

Sample Location

(c)











0481plusmn 0140 1174 (0005) 450 (0007) 0168plusmn 0289 034 (0572) 042 (0928)


Biddle

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264plusmn 111 42






0

2

4

6

8

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Eu

dico

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Eu

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aceo

us sh

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Ro

ots

Mo

ss

Ha

ir

Du

st

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Plastic

Ba

rk

Th

read

Am

ou

nt

of

mat

eri

als

wit

hin

eac

h r

egi

on

(g)

Nest Composition

Total

Outer Nest

Cup

(a)

0

10

20

30

40

50

60

70

80

90

Eu

dico

t twigs

Eu

dico

t herb

aceo

us sh

oo

ts

Grass

Ro

ots

Mo

ss

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ir

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st

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Plastic

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n (

)

Nest Component

Outer Nest

Cup

(b)









0

05

1

15

2

Top Base Cup

Dia

me

ter

(mm

)Sample Location

(a)

0

5

10

15

20

25

30

Top Base Cup

Be

nd

ing

Stre

ngt

h

(Nm

x 1

0-3

)

Sample Location

(b)

0

500

1000

1500

2000

2500

Top Base Cup

Rig

idit

y (N

msup2

x 1

0-6

)

Sample Location

(c)











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Biddle

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0

2

4

6

8

10

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Eu

dico

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Eu

dico

t herb

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us sh

oo

ts

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Ro

ots

Mo

ss

Ha

ir

Du

st

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Plastic

Ba

rk

Th

read

Am

ou

nt

of

mat

eri

als

wit

hin

eac

h r

egi

on

(g)

Nest Composition

Total

Outer Nest

Cup

(a)

0

10

20

30

40

50

60

70

80

90

Eu

dico

t twigs

Eu

dico

t herb

aceo

us sh

oo

ts

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Ro

ots

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)

Nest Component

Outer Nest

Cup

(b)









0

05

1

15

2

Top Base Cup

Dia

me

ter

(mm

)Sample Location

(a)

0

5

10

15

20

25

30

Top Base Cup

Be

nd

ing

Stre

ngt

h

(Nm

x 1

0-3

)

Sample Location

(b)

0

500

1000

1500

2000

2500

Top Base Cup

Rig

idit

y (N

msup2

x 1

0-6

)

Sample Location

(c)











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0

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Top Base Cup

Dia

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(mm

)Sample Location

(a)

0

5

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Top Base Cup

Be

nd

ing

Stre

ngt

h

(Nm

x 1

0-3

)

Sample Location

(b)

0

500

1000

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2000

2500

Top Base Cup

Rig

idit

y (N

msup2

x 1

0-6

)

Sample Location

(c)











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0

05

1

15

2

Top Base Cup

Dia

me

ter

(mm

)Sample Location

(a)

0

5

10

15

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Top Base Cup

Be

nd

ing

Stre

ngt

h

(Nm

x 1

0-3

)

Sample Location

(b)

0

500

1000

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2000

2500

Top Base Cup

Rig

idit

y (N

msup2

x 1

0-6

)

Sample Location

(c)











0481plusmn 0140 1174 (0005) 450 (0007) 0168plusmn 0289 034 (0572) 042 (0928)


Biddle

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0481plusmn 0140 1174 (0005) 450 (0007) 0168plusmn 0289 034 (0572) 042 (0928)


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Documents

Construction patterns of birds’ nests provide insight into ... › articles › 3010.pdf · during bending. For the nest walls, samples were taken from sides both parallel and perpendicular