The Auk 115(2):490-494, 1998
Chick Recognition in American Avocets:A Chick-exchangeStudy SZABOLCSLENGYEL,TMJULIEA. ROBINSON,2'5AND LEWIS W. ORING3
•Behavioural EcologyResearch Group,Department of Evolutionary ZoologyandHumanBiology,KossuthUniversity, Debrecen, Egyetemtdr 1. 4010, Hungary; 2Ecology, Evolution andConservation Biology Program,1000ValleyRoad,University ofNevada, Reno,Nevada89512, USA; and
3Ecology, Evolution andConservation BiologyProgramandDepartment of Environmental andResource Sciences, 1000ValleyRoad,University of Nevada, Reno,Nevada89512,USA
Chickrecognitionis centralto anunderstanding of recognitionexistsin AmericanAvocets,and if so,to why adoptionoccursin birds.If adultsdiscriminate estimateits timing during chickdevelopment. between their own and alien chicks, the chance of a Methods.--Fieldexperimentswere conducted at chickbeingadopteddecreases (Pierotti1988).In con- JayDow, Sr.Wetlands(40ø10'N,120ø20'W)in Lassen trast, lack of recognitionmay result in a high fre- County,California, in 1993 and 1994.Details of the quencyof adoption.Severalhypothesesconcerning studysiteand generalfield methodsare availablein adoptionmake predictionsaboutchickrecognition. Robinsonand Oring (1997).All chicksused in exThe nonadaptive"side-effect"hypothesissuggests changetrialswereindividuallycolor-banded. Twenthat adultsdo not recognizetheir own offspring(Ea- ty adults(38.5%of total populationof 26 pairs)were die et al. 1988,Choudhuryet al. 1993).Adultsshould color-banded, with one or both adults marked at 12 recognizetheir own offspring and those of related nests.We followedbrood movementson a daily baadultsif adoptionis basedon kin selection(Holley sis. 1984).If adultsarereciprocalaltruists,i.e.theyadopt Basedon observationsof aggressionby adults tochicksof adultsthat might providea similarservice ward olderchicksin 1993,and pilot trials in early (Trivers 1971), they should recognizetheir young 1994,we divided experimentalchicksinto two age and the offspringof other altruists.The "intergen- groups:-8 days erationalconflict"hypothesis(Pierottiand Murphy old ("old" group). In fosteringtrials, chickswere 1987) predicts that adults should recognize their transplantedto a differentbrood(referredto as"resyoung and rejectunrelated young in order to direct ident" chicks), whereas control chicks were reintroparentalcareto their own offspring. duced to their own family. We used same-aged The potentialfor adoptiondependson the age at chicksin fosteringtrials to eliminatethe confoundwhichchickscanbe recognizedby theirparents.The ing effect of body-sizedifferencesbetweenthe exonsetof recognitionusuallyis synchronized with the perimentaland the residentchicks.Thus,our 2 x 2 onset of brood mobility, as in semiprecocialgulls factorial experiment design had two levels of age (Gravesand Whiten 1980),or at fledging,asin altri- (young and old) and two levelsof treatment(foster cial passerines(Burtt 1977, Balda and Balda 1978, and control). Beecheret al. 1981).The timingof chickrecognition Chicksand familieswere used in only one trial. alsois important from a conservationviewpoint be- Experimentalbroodsand chickswere chosenat rancauseit gives information on the potential for arti- dom. Wedeterminedthe agegroupand selectedthe ficial adoptions or intraspecificcross-fosteringof experimentalchick first, and the treatment (control chicksin threatenedor endangeredspecies.To our vs. fostered)second.If a fosteringtrial was selected, knowledge,chickrecognitionhas not been studied we randomlychosea fosterfamily. Chickswerecapexperimentallyin precocialshorebirds. tured by hand,transportedto the locationof the fosAmerican Avocet (Recurvirostraamericana)chicks ter family,and exchanged with a chickfrom the fosare precocial.Soonafter chickshatch,adultsmove ter family (replacedchickswere kept at the obsertheirbroodsfrom thenestto feedingterritories(Len- vationpoint). After a 10-min acclimationperiod, we gyel 1995). Adoptionsfrequently take place during used instantaneoussamplingevery 15 s for 15 min broodmovementsat our study site.In 1993and 1994, to record the behavior of the adult closest to the fosrespectively,19.8%(n = 106)and 32.2%(n = 115)of ter chick.Becauseaggressivebehaviorwas brief in broodscontainedat leastoneadoptedchick.Because pilot trials (durationof "alarming"behavior,• - 7.3 chick recognitionis crucial to an understandingof + SD of 2.65 s, n = 6; chasing,:g= 1.8 ñ 0.40 s, n = how and why adoption occurs,we conducteda 3), we believethat 15-speriodswere enoughto enchick-exchange experimentto reveal whetherchick sureindependence betweensequentialobservations. We also estimated 4 E-mail:
[email protected].
edu
distance between
the closest adult
and the chick.
In controls,the experimentalchickwasreturnedto • Present address:Earth ObservationsProgram, JohnsonSpace Center, 2400 NASA Road 1, C23, its own family after a 15-min period, and the same Houston, Texas 77058, USA. samplingmethod was used after the 10-min accli49O
April 1998]
ShortCommunications
mation period. After trials, both experimentaland replacedchickswere returnedto their natal families. Chick behaviorwas monitoredduring the 10-min acclimationperiod. Three chick behaviorpatterns were observed:(1) the chickquickly ran away from the fosterfamily,(2) the chickremainedcrouchedin one place,and (3) the chickstayedwith and/or followed the family. In the first two cases,no interactionsoccurredbetweenthe fosterparentand theexperimental chick,whereasinteractionsoccurredbetween them in the third case.In the latter case,foster
chicksusuallybeganfeedingwith theresidentchicks and reacted to the adults' calls. Based on these ob-
servations,we decideda priori to conducta trial only if some form of interaction
occurred
between
491
TABLE1. Frequencyof acceptancebehaviorsby adult American Avocets toward control (n = 12)
and fostered chicks(n = 14) (age groups combined). Data are percentages(œ_+SD). Behavior
Vigilance Calling Leading Protecting Brooding • Kruskal-Wallis
Control
Fostered
66.8 _+18.52 65.1 +_16.89 9.0 +_5.53 5.1 +_9.10 5.2 +_7.65 1.6 _+4.37 0.9 +- 1.63 1.8 +_3.55 2.2 +- 6.61 0.0 +- 0.00
Ha
pb
0.32 5.87 2.58 0.25 --
0.816 0.059 0.367 0.816 --
test.
bSignificance levelsadjustedfor experimentwise errorusingthesequentialBonferronimethod.
the
parent and the foster chick during the acclimation period, i.e. the chickactedaspart of the fosterfamily. 1.49%in controlsand 19.6 _+1.38%in fosteringtriWe divided adult behavior (defined after Hamilals) did not differ between treatments (two-way ton 1975)into three groups:(1) acceptance(brood- ANOVA, F = 2.06, df = 3 and 22, P = 0.135). The ing, calling, leading, protecting, vigilance), (2) in- effect of treatmentwas marginally significant(F = difference(feeding,flying, preening,walking), and 3.70,df = 1 and 22, P = 0.067)and that of chickage (3) aggression("alarming," chasing).If adults be- was not (F = 1.74, df = 1 and 22, P = 0.200). Each haved aggressively toward the experimentalchick, indifferentbehaviorwasequallylikely in thecontrol the chick was consideredrejected.Otherwise,the and fosteredgroups(Kruskal-Wallistests,P > 0.17 for eachbehavior). chickwas consideredaccepted. Adults did not show aggressivebehaviorto their Six control and sevenfostering trials were completedin both agegroups(26 trialstotal).The mean own chicks.However, 6.9% of the behaviorsrecorded ageof youngchickswas4.5 _+SD of 1.87daysin con- in fostering experimentswere aggressive.Aggrestrols (range 2 to 7 days),and 4.7 _+1.80 days (range sionusually startedwith alarm-callingby the adults toward the foster chick.Later, adults peckedat the 2 to 7) in the fosteredgroup (t = -0.21, df = 11, P = 0.837).The mean age of old chickswas 12.0 +_3.23 chick, which was observedin each trial where agdays (range8 to 16) in controlsand 11.7 _+3.04 days gressionoccurred.However,peckingwas recorded (range8 to 17) in the fosteredgroup (t = 0.41, df = in the behavioralsampleonly twice,becausethisbe11, P = 0.689). havior (which lastsfor
