The accumulation of old nest material might affect nest-site selection and nest building by hole-nesting birds, so we tested this hypothesis by manipulating the ...
The Auk 113(2):319-328, 1996
OLD
NEST MATERIAL
EFFECTS
IN NEST BOXES OF TREE SWALLOWS:
ON NEST-SITE
CHOICE
AND
NEST BUILDING
WALLACE B. RENDELL • AND NICOLAAS A. g.
VERBEEK
Behavioral EcologyResearch Group,Departmentof Biological Sciences, SimonFraserUniversity, Burnaby,BritishColumbiaV5A 1S6,Canada
ABSTR•CT.--Innatural cavities,old nest material accumulateswith successive use,thereby reducingthe size of the cavity,and allowing the numbersof certainhaematophagous ectoparasitesto increase.For this reasonand becauseresearchers studyingbirdsbreedingin nest boxestypicallyremoveold nestsfrom boxes,the resultsof suchstudieshavebeenquestioned. The accumulationof old nest materialmight affectnest-siteselectionand nestbuilding by hole-nestingbirds, so we testedthis hypothesisby manipulatingthe presenceand amount of old nest material in nestboxesof Tree Swallows(Tachycineta bicolor).Our experimentalso allowed us to examinewhether costsare incurredby femalesdue to nestbuilding in terms of their subsequentreproductive output. When a choice of boxeswas available, swallows preferred empty and clean boxes,or those where the old material had been microwaved, over those with old, untouched material. Clean boxes and those with microwaved material
had morespaceinside,soour experimentssupporttwo hypotheses:swallowsavoidpotentially high numbersof parasitesin nestswith old material;or they prefer large cavities.Empty
boxesaffectednestbuilding.The massand volumeof nestsbuilt in cleanboxeswere greater than for nestsbuilt on old material.Femalesdid not add more feathersto the nestlining in boxeswith old materialas comparedwith cleanboxes.Correlationanalysessuggested that femalesbuilding large nestsbegan egg laying earlier in both years.Otherwise, there were no associations between the sizesof nestsbuilt by femalesand subsequentreproductive output (e.g. clutch size) or nestlingsize (e.g. body-conditionindex). Our resultsshow that the common habit of removing old nests from boxescan affect nest-sitechoice and nestbuilding behavior.Nest building doesnot influencereproductiveoutput by Tree Swallows. Received16 May 1995,accepted21 August1995.
ifications for an individual's future reproduc-
Until Meller's (1989) critique, one cavity characteristiclargely ignored was that of old nest material. Becauseresearcherstypically re-
tive effort and success.Nest-site characteristics,
move old nest material
suchascavityorientation(Luresden1986,Rendell and Robertson 1994a) and cavity size
each breeding season,Moller statedthat individuals that nest in boxesexperienceunrealistically beneficialbreedingconditions.In natural
NEST-SITE SELECTION is an important compo-
nent of breedingbehaviorthat may haveram-
(Karlsson and Nilsson 1977, Rendell and Rob-
from
nest boxes after
cavities, old nest material accumulates with successive use, and so do the numbers of some
ertson 1993), are extremely variable in natural populations,and have been shown to affectnestsite choiceand reproductionfor many species of cavity-nestingpasserines.Becauseexperimental manipulationof natural cavitiesmay be impractical,or impossible,manipulation of the
typesof haematophagous ectoparasites (e.g.bird fleas;unpubl. manuscript).Studieshaveshown that many typesof parasitescanreducethe reproductivesuccess of cavity nesters(e.g. Moss
characteristics
researchers
and Camin 1970, Richner et al. 1993, Winkler
in nest-site
1993).Many importantlong-termstudiesof life history have been done using cavity-nesting
to examine
of nest boxes allows
how extreme
variations
qualitiesinfluencethe breeding ecologyof cavity nestersand,therefore,to gatherinsightsinto reproductiveeffort and the evolution of life histories.
birds in nest-boxpopulations,so it is important to assessthe possibleeffectsof old material on the breeding ecologyof cavity nesters,and to consider
• Presentaddress:Department of Biology,Queen's University, Kingston,Ontario K7L 3N6, Canada. 319
whether
or not such studies
could or
should be reinterpreted. Cavity-nestingbirds may frequently have a choiceof nest sitesin which to breed, perhaps becausetheir territory includes two or more
320
RENDELL •,I•DVERBF•K
cavities (e.g. Rendell and Robertson 1994b). Given that parasitescan reduce reproductive success,and that some parasitesare more numerousin old nests,cavity-nestingbirds may discriminatebetweenhigh and low infestations of parasites,and so avoid cavitieswith old material. Some birds that reuse nests--such
as Barn
[Auk,Vol. 113
of old nest material, to test the assumption that
parasitesare more numerousin boxeswith old nests (cf. Moller 1989). We found that bird fleas were
more
numerous
Swallows(Hirundorustica; e.g.Barclay1988),Cliff Swallows(H. pyrrhonota; e.g. Brownand Brown 1986),and Great Tits (Parusmajor;Oppliger et al. 1994)--can discriminate between nest sites
in boxes with
old
nest
materialcomparedto cleanboxes,whereasblow flies and fowl miteswere equally numerousin all box types(unpubl. manuscript). METHODS
Species studied.--TreeSwallowsare sociallymonog-
with and without high numbersof parasites, amous, single-broodedinsectivoresthat have been and they avoid the former. studied extensivelyin box and cavity populations The accumulation
of old material
shrinks
cav-
ity size. For some cavity-nestingbirds, clutch
sizeispositivelyassociated with cavitysize(e.g. Rendell and Robertson 1993, Rendell and Ver-
beek 1996), so these birds may prefer cavities with
less old material.
Benefitsof energysavingsin usingnestswith old material may outweigh potential costsof nest reuse due to ectoparasitismand smaller cavitysize.By reusingan old cavity,cavitynestersmight devotetheir energiesto foragingand egg production. Nest building has long been considered energetically costly. However, whether nestbuilding is costlyin termsof reproductive effort within a breeding season,or between seasons, remains unknown. To date,
no conclusiveevidence for a reproductive cost
due to nest building exists(Winkler and Wilkinson 1988, Conrad and Robertson 1993).
Alternatively, old material may not influence nest-siteselectionif, for example,the birds clean
(Robertson et al. 1992).Females build the nest,mainly usingdeadgrasses.Malesand femalescollectfeathers to line the cup. Femalesapparentlytime egg laying for the middle of May to takeadvantageof favorable environmentalconditions,andpossiblyto benefitfrom synchronousnesting (Stutchbury and Robertson 1987a,1988).Tree Swallowsat our studysiteare hosts to threetypesof haematophagous ectoparasites: blow flies (Protocalliphora sialia),northern fowl mites (Ornithonyssus sylviarum),and bird fleas (Ceratophyllus idius),which will be describedin greater detail in a forthcoming manuscript. Study site and box types.--We conducted this researchin marshhabitatat the CrestonValley Wildlife Management Area (CVWMA), British Columbia (49ø05'N, 116ø35'W), in 1991 and 1992. Tree Swallows
had bred in about 160 plywood and wood boxeson dikes
at CVWMA
for
a decade.
Our
boxes
were
mounted 1 m off the ground on wooden postswith metal predator guards.All the boxeswere within 40 m of water. In 1991 we arranged the boxesin pairs for a box-preferenceexperiment. In 1992 the boxes were redistributed;125 boxesof two types were arrangedsinglyand alternately,30 to 40 m apart,along dikes. Tree Swallows occupied all 79 territories in
out old nests(e.g. HouseWrens,Troglodytes aedon;Thompsonand Neill 1991,Johnson1996), 1991, and 112 of 125 (90%) boxes in 1992. or if they constructnew nestsof plant materials We usedfour typesof boxesduring 1991and 1992: (e.g. EuropeanStarlings,Sturnusvulgaris;Clark (C) clean;(S) sham(1991only); (CI) cleanwith inserts 1991)and animal materials(e.g. Tree Swallows, (1992only; seebelow); and (O) old boxes.In C boxes, Tachycineta bicolor; Winkler 1993)that deterpar- the old nestswere removedand the inside wasswept asitism.
with a wire brush to loosenall duff and droppings.
Here, we presentthe resultsof experiments on how old nest material
influences
box selec-
tion and nestbuildingby TreeSwallowsbreeding in BritishColumbia.Because we also recorded the reproductive successand nestling size of Tree Swallowsduring this study (Rendell and Verbeek 1996), we will
examine
whethernestbuilding wascostlyto femalesin terms of their current reproductiveoutput. In contrastto studiesperformed simultaneously with ours(e.g.Oppliger et al. 1994),we manipulatedparasiteloadsin boxesindirectly,by experimentingwith the presenceand abundance
Care was taken to clean in the cracks of boxes, where
possible,to kill or flushout hidden parasites.S boxes received the sametreatment as C boxesexcept that, after cleaning,one microwavednestwasinserted.We collected 50 old nests from boxes at CVWMA, and
microwaved each one in a Look cooking bag for 5 min on high power in a Toshibaoven. Old nest material
was available
at CVWMA
because
the boxes
were not cleaned after the 1990 breeding season.To determinethe effectiveness of this procedure,we sifted 3 of the 50 nests (each of which had living arthropodsbeforemicrowaving)after microwaving.All of the arthropodsin thesenestswere dead, so we are confident that this procedure killed parasitesin all
April1996]
Reuse ofOldNests byTreeSwallows
50 nests.O boxeswere not manipulatedin any way; the old nest material was left in place and the boxes were not cleaned.
Nest material
used at both S and O
321
feathers collected for new nestswas determined by counting the rachisesin sifted nests.Feathersthat were obviouslypart of an old nest structurewere not
boxes showed evidence of occupancythe previous
counted.
year (e.g.deadnestlingsand bird droppings).Therefore, any parasitesin theseboxespresumablywould have had accessto hostspreviously,and could have
1991 (nc = 18, ns = 8, no = 4), and 100 nests in 1992 (nc = 34, nc•= 13, no = 53).
increased in number.
Nest-box preference experiment.--We performeda boxpreferenceexperimentusing C, S, and O boxesin 1991. The boxeswere distributed in pairs with each box in a pair 3 m apart, and pairs 40 m apart. We calleda pairof boxesa territory.Thisdesignprovided a choiceof boxesto eachpair of swallows.The boxes were pairedas follows:C with O on 29 territories;C
Feather
counts
were
made
for 30 nests in
Costof nestbuilding.--Elsewhere (Rendell and Verbeek 1996), we describethat, when comparing the reproductivesuccess of birdsusingthe four boxtypes, we switched nests under females in an attempt to control for possiblecovariationbetween the phenotype of females,their reproductivesuccess,and the box type they chose.This procedurewas done after nest sites were chosen and new nests were built, but
beforeegg laying. with S on 25 territories; and S with O on 25 territories. For the purposesof analyzing reproductiveoutput We arrangedthe threetypesof territoriessequentially after nestbuilding in our study,we excludedfemales involved in nest switches, because the new microthroughoutthe marsh:C x O1, C x S1, S x O1, C x 02 ..... etc. All boxeswere in place by 25 March, environment of their altered nest and box could have before the swallowsbegansettling.We determined influencedbreeding.We alsoexcludedfemaleswhose boxpreferenceaccordingto the boxin which a female approximateagewas unknown. Therefore,our analbuilt her nest and laid her clutch. At one territory a ysis of costof nest building is basedon the repropair of Black-cappedChickadees(Parusatricapillus) al- ductiveoutput of 34 femalesin 1991,and 85 in 1992. Bandingandfemaleage.--We capturedfemalesby readyoccupiedone of the boxesbeforeTree Swallows settledat the other box, sothis territory was dropped hand, in mist nets, and using box traps(Stutchbury and Robertson1986).They receivedCanadianWildfrom the analysis. Nest-building experiment.--Weconductedan exper- life Service (CWS) aluminum bands and were indiiment with box insertsin 1992to examine how cavity vidually identified with nontoxicacrylicpaintsat posize influenced the size of new nests.In 15 randomly sitionson the wing and tail. Femaleswere sexedand to Hussell(1983)andStutchbury and chosenC boxes(hereafter designatedCI), compact agedaccording styrofoamand a plywood floor overlay were inserted Robertson(1987b). They were aged as second-year (SY) and after-second-year(ASY) birds in 1991, but to fill the bottom 8 cm of each box. Therefore, CI boxes recapturesin 1992 allowed us to divide female ages were clean, but they simulated the smaller cavity of SY,ASY(includingthird year),and boxeswith old nest material. The depth of the inserts into threeclasses: after-third-yearbirds (ATY, including fourth year). approximatedthe mean depth of old nest material in O boxes in 1992 (œ= 7.4 + SE of 0.3 cm, n = 58). Two Breeding and nestlingsize.--We recordedbreeding phenologyand reproductivesuccess during regular CI boxeswere not usedby Tree Swallows. We recordedthe mass(g) of all new nestsbuilt nestchecks(i.e. conductedeachday during egg laying, hatching,and fledging;everythreedaysduring oncethe nestcupswere formed,but yet unlined. New and old nestswere distinguishedeasily, and nest incubationand nestlingperiods).Variablesrecorded structureswere relatively dry when weighed. We included:datesof first egg,hatching,and fledging; weighed nestsin a ZIPLOC bag with a Pesolascale durationof incubationand nestlingperiods;number fledglings, anddeadyoung;and (50-300 g), and then replacedthem in boxesintact. of eggs,hatchlings, Many nestsbuilt on top of old nest material were percentagesof hatchlings/eggslaid, fledglings/ and fledglings/eggs laid.The first-hatchvery light and fragile, so we had to estimatetheir hatchlings, day mass(i.e. 1 or 5 g) becausehandling would have ing daywasnestlingday(ND) 1. First-fledging destroyed them. The estimateswere based on the was the date when the first nestling left the nest. Incubationperiodwasthe number of daysfrom when massesof three neststhat were weighed despitetheir small size. the last egg was laid to first hatching,and nestling We repeatedlymeasuredthe depth (cm)of new and period was the number of days between ND 1 and old nest structures in each box before the settlement the day the last nestling fledged or died. of pairsin boxes,until the new nestswere completed. We bandednestlingswith CWS bandson ND 15. (1) younghaveattained Using the dimensionsof eachbox and the depth of Thisdaywaschosenbecause: new and old nests in a box, we calculated the volume peak structuralsize, and they are closeto peak mass of new and old nest structures(cm3),and the cavity (Zach and Mayoh 1982);and (2) the first young may (cm3) above the floor or nest material before settle- fledgefrom a nest on ND 16 (Rendell and Verbeek ment and beforeegg laying. 1996).Duringbandingwe measuredtheflattenedwing Feathers.--We collectednestsafter a breedingat- length(i.e. from "wrist" to tip of ninth primary,mm), tempt failed or the young fledged.The number of ninth primary length (i.e. from insertion point of
322
RENDELL A•4DVERBEFaC
TABLE 1. Boxtypeschosenby TreeSwallowsat pairedbox territories in 1991.Boxtypesare: (C) clean;(S) sham;and (O) old. P-values are binomial probabilities, and are the same for box type and size tests.
[Auk, Vol. 113
TABLE2. Mass (g) and volume (cm3) of new nest material gatheredby female Tree Swallows.Values are f + SE (n nests).a
Box type
Mass
Box chosen
Volume 1991
Territory
n
C
S
O
P
C x S C x O S x O
25 a 29 25
18 22 --
6 -19
-7 6
0.011 0.004 0.007
• One territory was excludedbecauseanotherspeciesoccupiedone box prior to settlementby Tree Swallows.
primary in manus to tip of primary, mm), and mass (g) of nestlings.For a structural measureof size of young,we subtracted ninth-primarylengthfromwing length to get manuslength (Pettingill 1985).For an index of body condition for individual nestlingswe used the following equation: mass/(manusp (cf. Slagsvoidand Lifjeld 1988). Statisticalanalysis.--Tominimize the possible effectsof season(Stutchburyand Robertson1988,Lombardo1994),we analyzedonly nestsin which the first egg was laid before 1 June.Also, renestingattempts by femaleswhose first attempt had failed were not includedin any analyses.The nest-buildingdatawere not combined between years due to differences in experimentalprotocol.The dataon reproductivesuccesswere not combinedbetween yearsbecauseof the experimental differences,and becauseseveral measuresof reproductivesuccess and nestlingsize were significantly different between years (Rendell and Verbeek 1996).We combineddata for all female age classesbecausethere were no significant differences in reproductivesuccess or nestling size among them within boxesand years (Rendell 1992),and because female age-classdistributions did not differ between box types, before or after nest switcheswere made (seebelow).For analysis,within-nest meanswere calculatedfor all nestling size variables.We used nonparametricstatistics(SAS Institute 1985, Siegel and Castellan 1988), and a significancelevel c• of 0.05. After correlationanalyses,we appliedsequentialBon-
Clean Sham Old
24.2 _+ 1.8^ (40) 4.8 -+ 1.3B (25) 5.9 _+ 1.4B(13)
Clean Clean(I) Old
26.3 _+ 1.3^ (40) 16.4 ___1.4B(13) 6.3 _+0.7c (58)
827.1 -+ 34.0^ (39) 307.7 -+ 54.2B(22) 428.7 -+ 75.43 (12)
1992
712.6 -+ 25.9^ (39) 581.6 -+ 27.5B(14) 287.2 -+ 24.9c (58)
' P < 0.001 for both parameterswithin both years (Kruskal-Wallis tests,two-tailed,df • 2). Valueswith the samecapitalletter are not different(P < 0.05,multiple-comparison method;Siegeland Castellan 1988).
control (i.e. the difference in cavity size between boxes). Both S and O boxes had old nest
material,sotheir cavitysizeswere alwayssmaller than C boxes. On 17 territories
with
both S
and O boxes, the S box had less old nest material
and,therefore,largercavitysizethan the O box. On five territories
with
S and O boxes this was
reversed,and on three territoriesthe cavitysizes were the same between
boxes. For each of the
three typesof territories,we analyzedboxpreferencewith respectto cavity size of each box. The swallowsmore often chosethe box in a pair
with the larger cavity (seebinomial probabilities in Table 1).
Femaleage, and presumablyexperience,did not affect the choice of nest sites. The numbers of ASY and SY females that chose C versus S
and O boxeswere not significantlydifferent (2 x 2 test, Pearson X2 = 0.29, df = 1, P = 0.59). To meet all the requirements for a valid chi-
squaretest(SiegelandCastellan1988),we combined the numbers
of ASY and SY females in S
ferroni correction tests (Rice 1989) to determine ta-
and O boxes, so the test was between the dis-
blewide significancelevels and minimize the likelihoodof committinga type-I error.Wheresamplesizes vary betweentests,this is due to missingvalues.
sus those in boxes with
tributionsof agesof femalesin cleanboxesverold material.
Nest building.--Boxtype significantly influenced the volume and mass of new nest material
brought to nests.Femalesusing C boxesbuilt
RESULTS
Nest-boxpreference.--Nest-box choice was nonrandom for all three paired-box combinations (Table 1). C boxes were preferred over both S and O boxes,and S boxeswere preferred over O boxes. These results biased
because
of a variable
could that
have been we did
not
significantlylargerand heavierneststhanbirds usingS or O boxesin 1991(Table2). Nestsbuilt in C boxesin 1992were significantlylargerand heavier than those built in CI boxes, and new
nestsin CI boxeswere significantly larger and heavier
than
those in O boxes. The
mass and
volume of new nestsbuilt by femaleswere sig-
April 1996]
Reuse ofOldNests byTreeSwallows
323
TABLE3. Mass (g) and volume (cm3) of new nests TABLE4. Volume (cm3) of boxesabove the nest, after the completionof new nestsby female Tree Swalbuilt by older and youngerfemaleTree Swallows, lows. Values are • + SE (n nests).a irrespectiveof box type. Values are • + SE (n females).No significantdifferencesfound between femaleageclasses for massor volumewithin years Box type Volume (Mann-Whitney and Kruskal-Wallis tests, all P > 1991
0.59). Female
agea
Mass
Volume
Clean Sham Old
1,763 + 37A (37) 1,539 + 62B(19) 1,551 + 67' (12) 1992
1991
SY ASY
16.2 + 3.6 (10) 14.9 _+ 1.6 (63)
SY ASY ATY
13.7 + 2.6 (23) 14.0 _+ 1.3 (54) 15.9 _+2.5 (30)
597.8 + 93.8 (10) 601.9 + 45.4 (57)
Clean Clean(I) Old
1,888 + 33A (36) 1,205 + 40B(13) 1,515 _+ 36c (56)
1992
451.4 + 58.9 (22) 483.3 + 33.6 (54) 464.4 + 52.1 (31)
ßP < 0.005for both years(Kruskat-Wallistests,two-tailed,df = 2). Valueswith the samecapitalletter are not different(P < 0.05,multiplecomparisonmethod;Siegeland Castellan1988).
' Agesare:(SY)second-year; (ASY)after-second year,includingthird year;and (ATY) after-thirdyear,includingfourthyear.
df = 2, P = 0.28) affectedthe numbers of feathers
incorporatedinto new nestsby pairs in either year.
nificantly positively correlatedwith cavity size at settlement (massin 1991, Spearmanrank-order correlations, p = 0.76, n = 72; massin 1992, p = 0.72, n = 111; volume in 1991, p = 0.77, n = 72; volume in 1992, p = 0.67, n = 111; all P
< 0.001).Many femalesbuilding in boxesthat containedold materialbroughtlessthan 5 g of grassto the nest (1991, 16 of 25 S boxes[64%], 5 of 13 O boxes [38.4%]; 1992, 38 of 58 O boxes
Costof nestbuilding.--First,we reanalyzedour data to ensurethat the aspectsof the ecology of the subsetof femalesusedin the costanalysis reflected
those of all the females
combined.
Therewasa significantpositivecorrelationbetween cavity size at settlement,and nest mass (1991, p = 0.71, n = 31; 1992, p = 0.78, n = 84;
both years, P < 0.001) and nest volume (1991, p = 0.74, n = 31; 1992, p = 0.71, n = 84; both
[65.5%]).Theseindividualsmerely lined exist- years,P < 0.001)of new neststhat femalesbuilt. ing material with a thin layer of grassand then The masses and volumesof nestsbuilt by older added feathers.
Female age did not affect nest mass (1991, Mann-Whitney [M-W] U-test,U = 0.53,P = 0.59;
and younger femaleswere not different (all P >- 0.60). In both years,the age distributionsof femalesusingthe three boxtypeswere not dif-
1992, Kruskal-Wallis [K-W] test, H = 0.44, df = 2, two-tailed, P = 0.80) or volume (1991, U =
ferent (all P >- 0.83).
0.12, P = 0.90; 1992, H = 0.59, df = 2, two-tailed,
First-eggdatewas negatively correlatedwith the massof new nestsbuilt by femalesin 1992
P = 0.74) in either year, when all boxeswere combined (Table 3).
After new nestswere completed,cavity size above the nest material was still significantly TABLE5. Numbersof feathersincorporatedinto new greater in C boxesthan in S and O boxesin 1991 (K-W test, H = 12.0, df = 2, P < 0.005), and
greater in C boxesthan in CI and O boxesin
nestsby Tree Swallows. Values are • + SE (n nests;
range). No significantdifferencesfound between box types for numbers of featherswithin years (Kruskal-Wallis tests,all P > 0.21).
1992 (H = 51.0, df = 2, P < 0.001; Table 4).
Remaining cavity sizes were not different between S and O boxesin 1991, but were significantly greater in O boxescomparedto CI boxes in 1992(multiple-comparisonmethod,P < 0.05; Siegel and Castellan1988). Feathers.--Neitherbox type (1991, K-W test, H = 3.2, df = 2, P = 0.21; 1992, H = 3.0, df = 2,
P = 0.23; Table 5) nor female age (1991, M-W test, U = 0.2, P = 0.84; 1992, K-W test, H = 2.6,
Box type
Number of feathers 1991
Clean Sham Old
138 + 8 (18; 84-186) 157 + 23 (8; 73-286) 241 + 50 (4; 95-318) 1992
Clean Clean(I) Old
139 + 9 (34; 62-317) 116 _+ 11 (13; 61-183) 118 + 7 (53; 34-278)
324
RENDELL ANDVERBEEK
[Auk, Vol. 113
TABLE6. Correlationsbetweenselectedvariablesof nestingphenology,reproductiveoutput, and nestling size with the mass(g) and volume (cm3)of new nestsbuilt by female Tree Swallows.Valuesare Spearman's rank-order correlation coefficients,p (n females). Variable
Mass
Volume
1991
First egg date Incubation period (days) Nestling period (days)
-0.13 (34) -0.40 (30) 0.22 (28)
-0.34 (31) -0.36 (29) 0.25 (27)
Clutch size
0.11 (33)
0.26 (31)
Number fledglings/clutch size Nestling conditionindex'
0.06 (30) 0.07 (29)
-0.04 (29) 0.03 (28)
1992
First egg date Incubationperiod (days) Nestling period (days)
-0.31' (83) -0.08 (80) -0.07 (69)
-0.27 (84) -0.02 (81) -0.03 (69)
Clutch size
0.15 (81)
0.07 (82)
Number fledglings/clutch size Nestling conditionindex
0.02 (80) 0.01 (68)
0.11 (81) -0.06 (68)
ßIndex = mass/(manus)•; see Methods for more details.
* P = 0.004;table-widecorrectedc•= 0.008after sequentialBonferronicorrection(cf. Rice I989).
(Table 6). Otherwise, there were no significant associationsbetween nesting phenology, subsequent reproductive output, or nestling size on ND 15 in either year (Table 6; 1991,all P ->
George1991,Loyeand Carroll 1991],BarnSwallows [Moller 1987, 1990,Barclay1988,seealso Shields 1984, Shields and Crook 1987]) and Great
Tits (Christe et al. 1994, Oppliger et al. 1994), Tree Swallowshave evolved the ability to dissequentialBonferronicorrections; cf. Rice1989). criminatebetweennestswith high and low parFurther, we performed partial correlationsof asitepopulations.On territorieswith shamand clutch size with nest mass and nest volume, old boxeswhere cavitysizeswere similar,Tree when controlling for female age, first-eggdate, Swallows avoided boxeswith old, unmanipu0.03; 1992, all P -> 0.01; corrected c• = 0.008 after
and cavitysizeat settlement.We foundno sig-
lated nests. The cue that enabled Tree Swallows
nificant
to distinguish between microwaved and un-
correlations
between
these
variables
(1991, all P -> 0.14; 1992, all P -> 0.35).
manipulatedoldnestsmayhavebeenthe movement of adult fleas, both in the existing nest
DISCUSSION
structure or on the outside of a box. W.B.R. once
observedtens of adult fleassurrounding a box Tree Swallowsclearly preferred clean boxes entrancein early spring, presumablywaiting over thosewith old nest material, although our for a host.Analogousto observationsof cyclic experiment failed to determine if they were colonyuseby coloniallynestinghirundines(e.g. avoidingthe higherectoparasite populationsin Loyeand Carroll 1991),if somehole nestersin boxeswith old material (unpubl. manuscript), the wild avoid cavitiesbecauseof high parasite or if they were simply looking for the largest loads,this could be an explanationwhy many availablecavity.We found a significantpositive studiesinvestigatingcavityavailabilityfor seccorrelationbetweencavity size and clutchsize ondaryhole nestershave found numerous,unin eachyear when we combinedthe clutches occupied cavities in natural populations (e.g. from all box types(Rendelland Verbeek 1996). van Balen et al. 1982, Brush 1983, Ingold and Also, Rendell and Robertson (1993 and refer- Ingold 1984,Petersonand Gauthier 1985,Renencestherein) showed that Tree Swallows, like
dell and Robertson 1989, Waters et al. 1990).
otherspeciesof secondarycavitynesters,prefer to nest in large cavitieswhen a choiceis available,andthatfemaleslay largerclutchesin larger cavities. However, it is possible that, like other hirundines (e.g. Cliff Swallows [Brown
Contraryto Moller's (1989)hypothesis,studies have shown that somespeciesof hole-nesting birds may choosecavitiesindependentof the presenceor absenceof old nestmaterial(e.g. HouseWrens;Thompsonand Neill 1991,Johnson 1996), or actually prefer cavitieswith old
and Brown 1986, Emlen 1986, Chapman and
April 1996]
Reuse ofOldNestsbyTreeSwallows
325
nests(e.g.Eastern Bluebirds [Sialia sialis], Davi• greaterthan thoseof natural cavities(e.g. Robet al. 1994;Pied Flycatchers[Ficedulahypoleuca], Mappes et al. 1994; see also Jacksonand Tate [1974]for Purple Martins [Prognesubis]).Christe et al. (1994)suggestedthat parasitepopulations in the cavitiesused in such studiesmay have been so low as to be negligible, and so did not affectcavity choice,but we suggestfour additional hypothesesmay account for these unexpectedresults.As Mappeset al. (1994)showed, hole nesters may chooseboxes with old nests when large parasitepopulations are in "clean" boxes.Also, generic differencesin nest-building behavior may preclude the need for indi-
ertsonand Rendell 1990).Apparently, however, nest building is not costly to female Tree Swallows in terms of their subsequentreproductive output (seealso Lombardo 1994). Conrad and Robertson (1993) found a similar result
for an open-nester, Eastern Phoebes (Sayornis
phoebe). For many Tree Swallowsthis may be, in part, becausethey arrive on their breeding grounds up to one and a half months before the medianfirst-eggdateof the population.For example, in 1991, the first Tree Swallows arrived in our population on 17 March (W.B.R. pers.obs.),yet the mean first-eggdate that year viduals to locate clean cavities. To some holewasnot until 8 May (Rendelland Verbeek1996). nesting species--such as House Wrens, which Stutchburyand Robertson(1987a) experimenremoveold material from cavities(e.g. Johnson tally delayedsettlementat nestboxesby female 1996),and EuropeanStarlings,which line their Tree Swallowsin southeastern Ontario. They nestswith specificplant speciesthat deter par- reported a significant positive associationbeasites(e.g. Clark 1991)--the presenceor absence tween settlement date at nest sites and the date of old nestsmaybe immaterial.Further, cavities of the initiation of nest building, and a signifwith old nestsshowing evidence(e.g. nestling icant negative associationbetween settlement feces)of having been used successfullyin the date and the interval of daysuntil egg laying.
past may be judged as suitable for use again
So, by returning early in the spring, females may locateand secureclean large cavities,and nally, by choosingto use cavitieswith old nest build large nests over an extended period of material, somespeciesmay be avoiding inter- time, thusallowing them time to foragein prepspecificcompetition.For example,Tree Swal- aration for egg laying and incubation, despite lowsprefer cleanerand/or largercavities,House any extraeffortexpendedduring nestbuilding. Wrens show no apparent preference, and East- As is the casein our study,possibleearly arrival ern Bluebirdsprefer cavitieswith old material. and the building of large nestsmay be associInterestingly,all threespeciescompetedirectly ated with slightly advancedfirst egg dates(Taand intensively for cavities(Rendell and Rob- ble 6), but in general, most female Tree Swalertson 1990). lows time egg laying for the middle of May Tree Swallowsshowedgreatvariability in the (Stutchburyand Robertson1987a,1988). (Thompson and Neill 1991, Johnson 1996). Fi-
sizeof the neststhey built, a variable influenced
We caution
that our conclusion
that there
is
by boxtypeandcavitysize.Correlationsshowed no reproductivecostto nest building is based that nest size increasedwith cavity size. Lom- solely on correlations.A better test of the cost bardo (1994) found that Tree Swallows in south- of nest-building hypothesisin hole-nesting easternMichiganalsobuilt biggernests(e.g.by birds would be to assessclutch size and repronest volume) in bigger boxes.Pitts (1988) ob- ductive output of birds that arrive late on their served the same behavior in Eastern Bluebirds. breeding grounds,but must build a large nest Similar to Lombardo (1994), we found no effect in the short period of time that precedesthe of female age on the sizesof new nestsbuilt in mean first-eggdate of the population. Under boxes. The larger nests observed in clean or thesecircumstances, if there is a reproductive larger boxesmay be needed to ensure a stable cost to nest building, we predict a significant platform for the nest cup and eggs,to provide reduction in clutch size and reproductive outadequateinsulation, or to enable young and put. adultsto leave the box more easily. Feathersserve an important thermoregulaIt is likely that the observedsize of someof tory functionby insulatingeggsand nestlings the nestsin our study,as well as other studies (Capreo11983,Moller 1984).Winkler (1993)maof hole nesters, are an artifact of the size of nipulated the number of feathersin nest cups boxesusedby researchers;on average,the vol- of Tree Swallows and showed that nestlings umesof nestboxesprovided by researchersare with morefeathersin their nestcupswere larg-
326
RENDELL ANDVERBEEK
er and had fewer parasites(i.e. fowl mites, lice), indicating that feathersmay deter parasitefeeding. In our study, bird fleaswere more numer-
[Auk, Vol. 113
during that period (Rendell and Verbeek 1996). Feathers
can decrease the rate of heat loss in
Winkler's results, one might expect that birds should have incorporated more feathers into
nests (Capreol 1983), so during warm periods more feathersin a nest may be detrimental becausecavity temperaturescould be kept dangerously high. In support of this hypothesis,
these nests. However,
Lombardo (1994) found evidence that well-in-
ous in nests with old material and, based on
this was not observed
sulated nests(i.e. those with a greater volume fected (Rendell and Verbeek 1996); thus, our of nestmaterial) decreasedfledging success for results do not corroborate those in Winkler Tree Swallows late in the breeding season,pre(1993). Likewise, Lombardo (1994) found no as- sumably when high nest temperatures led to sociation between the numbers of feathers in hyperthermia in nestlings. nestsof Tree Swallowsand hatching and fledgThe results of our study lend some support ing success.Capreol (1983) also found that to Moller's (1989) critique of nest-box studies, feathers did not deter the blow fly Protocalli- and the habit of removing old nest material phorasialiafrom feeding on nestling Tree Swal- from nest boxes. Old nest material in nest boxes lows. Tree Swallows add feathers to the cup influences nest-site choice and nest-building lining until hatching, but not after, so it is pos- behavior in Tree Swallows. If nest building is sible that the birds in our study did not rec- periodically costly for individual hole nesters, ognize the higher flea loadsin boxeswith old measuredby their reproductive output, removmaterial until after the young had hatched, or ing old nests from nest boxes may affect the that flea numbersincreasedasthe nestling stage quantitative resultsof long-term studiesof lifeprogressed.However, we dismissthese two ex- time reproductionby hole-nestingbirds. planations becauseTree Swallows apparently and, furthermore, nestling health was not af-
discriminated between parasitized (O) and rel-
ACKNOWLEDGMENTS
atively unparasitized(S) nestsduring the boxThanksgo to everyonewho helpedwith thisstudy. preference experiment, and becausethere was P. Belton,P. A. Gowaty,H. MacCarthy,G. D. Schnell, no significanteffect of seasonon the numbers L. L. Wolf, R. C. Ydenberg,and three anonymous of the three types of parasitesfound in boxes reviewers commented on earlier drafts of this manuin this study (unpubl. manuscript).Our results script.C. Sabrosky,H. C. Proctor,and G. Chilton idendiffer from those of Winkler (1993) in another
tified the blow flies, fowl mites, and bird fleas, re-
way. He found a negativecorrelationbetween spectively.K. F. Conradand K. Holder offeredstatisthe duration of the nestling period and the number of feathers in a nest at hatching in each year of a three-yearstudy (significantin one of the three years), suggestingthat more feathers in the nestcup enableyoung to grow fasterand
fledgeearlier.We found no association between the number
of feathers
in a nest and the du-
tical assistance, and the former encouragedus to look more closelyat the issueof costsof nest building. P. Hurd, Y. Morbey, and S. Wilson helped in the field, and B. Beasleyand J. Sideflusallowedus to usetheir equipment.The BordenLaboratoryallowedus to use their microwave. W.B.R. extends a special thanks to R. Houtman, A. Rahme, A. and G. Vacca, and L. Ver-
beek for their generoushospitality and assistance. ration of the nestling period in 1991(Spearman CVWMA allowed us to use their land for the study, rank-order correlation, p = 0.03, n = 29, P = and provided logistic support. This researchwas 0.89), and a significantpositive correlationbe- funded by a Natural Sciencesand Engineering Retween these variables in 1992 (p = 0.29, n = 84, searchCouncil (NSERC) of Canadaoperating grant P = 0.007). We think that nestling periodswere to N.A.M.V., and an NSERC Graduate Scholarship,
longer for young in nestswith more feathers in 1992 because the feathers
contributed
to the
heat stressexperiencedby nestlings during a heat wave in June of that year, and this heat stresslikely slowed growth rates. The mean temperature in June 1992 was significantly warmer by almost 6øCthan that for June 1991 (unpubl. manuscript);temperatures exceeded 30øCfor nine consecutivedays,and mostof the incidents
of entire brood death in 1992 occurred
two SFU GraduateResearchFellowships,an SFU Special Graduate ResearchFellowship, an SFU Special GraduateEntranceScholarship,and a JohnK. Cooper Award
to W.B.R.
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