Decision‐making at the time of parasitism: cowbirds prefer to peck eggs with weaker shells

COSSA NATALIA A.; REBOREDA JC; FIORINI VD

ANIMAL COGNITION

SPRINGER HEIDELBERG

Lugar: HEIDELBERG; Año: 2022

1435-9448

Interspeci c avian brood parasites, like cuckoos and cowbirds, lay their eggs in nests of other species, the hosts, which take over the entire parental care of the parasite's eggs and chicks. This breeding strategy requires decisions that may a ect the parasite's reproductive success. During the breeding season, cowbirds search for host nests and revisit them to monitor its progress and parasitize at the time host laying begins. When visiting hosts nests, they repeatedly peck the nest contents trying to destroy one or more eggs. This behaviour favours parasite's o spring by reducing the competition for food with nestmates. We evaluated if the egg-pecking behaviour of female shiny (Molothrus bonariensis) and screaming (M. rufoaxillaris) cow- birds is a ected by the strength and the size of the eggs they nd in the nest. We presented to wild-caught females arti cial clutches with two natural eggs that di er in size and shell strength. We found that female shiny and screaming cowbirds adjusted egg-pecking behaviour based on the strength but not on the size of the eggs. When di erences in strength between eggs were high, both cowbird species pecked more frequently the egg with the weaker shell, increasing the probability of a successful puncture. Our results indicate that female cowbirds can discriminate eggs through the strength of the shell, and by choosing the weaker egg to peck, they increase the probability of puncturing.