Adopting Behavior and Breeding Biology of Avocets: Benefits of Large Broods for Good Parents?

摘要

Alloparental care, in which adults provide care for young that are not genetically related toudthem, is widespread in birds and mammals. Caring for unrelated young appears touddecrease the fitness of adopters and thus the behavior is difficult to explain based onudclassic evolutionary theory. I studied the evolutionary significance of adoption in avocetsud(Recurvirostra avosetta), a large-sized shorebird breeding on alkaline lakes in Hungaryudbetween 1998 and 2000. Thirteen percent of the chicks were adopted chicks and 21% ofudthe avocet families contained adopted young. Most adopted chicks left their own family toudgain adoption elsewhere, whereas some chicks were left behind by their parents. Moreudchicks survived in larger broods than in smaller ones. The survival of chicks that left theirudown family and their siblings remaining in the brood did not differ, whereas chicks thatudwere left behind reached the same survival as their siblings in the natal brood. The qualityudof the adults was also important, because pairs that later adopted chicks laid their eggsudearlier, occupied better territories and fledged more young than did non-adopting pairs.udExperimentally enlarged broods fledged more young than did modified or control broodsudin high predation sites. Incubating experimentally enlarged clutches of eggs requiredudhigher energy expenditure by parents. Therefore, I concluded that adoption may be audmeans to increase the size of the brood for certain, high-quality pairs without incurring theudcosts of producing and incubating more eggs. Adoption appears to provide fitness benefitsudto the adopting parents via an increase in brood size. However, adoption is not for everyudadu several correlative results and indirect evidence suggest that only high quality adultsudadopt. In conclusion, this study uncovered an interesting complexity underlying anudapparently erroneous behavior in the parental care system of avocets. The findingsudcontribute to an understanding of the evolution of the different forms of parental care andudthrow light on the possible evolutionary mechanisms that led to the current diversity ofudreproductive strategies in birds.