Egg tossing (behavior)

Egg tossing is a behavior observed in some species of birds and is related to infanticide. The activity is performed so as to increase the chances that newly laid eggs which are genetically closer to the female receive a better chance of survival. This behaviour is often seen in species that exhibit cooperative breeding.

During co-nesting, before a bird starts laying its eggs, it tosses out some eggs laid previously by another bird. As a result, the last egg-layers may contribute more eggs to the common nest. ["Cooperative Breeding in Birds: Long Term Studies of Ecology and Behaviour" (1990) Peter B. Stacey, Walter D. Koenig (eds.), ISBN 0521378907]

Among colonial non-co-nesting birds egg-tossing is observed to be performed by conspecific (of the same species) intruders. The tossing observed was non-accidental: the intruder rolled the egg to the edge of the nest by repeatedly flicking it with its beak. [Charles R. Brown, Mary Bomberger Brown (1996) "Coloniality in the Cliff Swallow: The Effect of Group Size on Social Behavior", ISBN 0226076253, [http://books.google.com/books?id=hCcmIanW0cYC&pg=PA142&dq=%22egg+tossing%22+bird&sig=UqCkGSYk5TuaAXdotwi0-1zIClY#PPA142,M1 p. 142] ]

It was concluded that in some species of cooperative birds egg-tossing is a strategy of clutch coordination: eggs are tossed until all birds in the common nest are ready to proceed with brooding, so that early egg-layers do not dominate the reproduction. [Walter D. Koenig, Janis L. Dickinson (2004) "Ecology and Evolution of Cooperative Breeding in Birds", ISBN 0521530997, [http://books.google.com/books?id=wz93GCISCWMC#PPA91,M1 p. 91] ]

Egg tossing by brood parasites

A slightly different behavior is that of brood parasite birds, such as some species of cuckoos: the cuckoo chick may toss host's eggs and even host's chicks out of the nest.

References