Selfish begging by screaming cowbirds, a mimetic brood parasite of the bay-winged cowbird

LICHTENSTEIN, G

ANIMAL BEHAVIOUR

Academic Press

Lugar: Londres; Año: 2001 vol. 61 p. 1151 - 1158

0003-3472

Molothrus rufoaxillaris are specialist parasites that almost exclusively parasitise bay-winged cowbirds Molothrus badius. Parasitic chicks are almost identical to the host young in their appearance and vocalisations until the chicks attain nutritional independence. This system provides an excellent opportunity to study the relationship between begging behaviour and hunger level for parasitic chicks and host young. Video analysis of laboratory experiments, compared the begging behaviour of the screaming and the bay-winged cowbird nestlings under controlled levels of food deprivation. They indicate that: firstly, the begging behaviour of both the parasitic chicks and the host young were influenced by their hunger level; secondly, the begging intensity of a focal chick was not influenced by the begging intensity of its nestmate; and thirdly the parasitic chicks begged more intensively than the host young for the same degree of hunger. The greater selfishness of the parasitic chicks is what would be expected from theory, because, unlike the host chicks, their greed will not be constrained by kinship with their nestmates or with the host parent?s future broods. Alternative hypotheses explaining intense begging in terms of parasitic chicks being more hungry, or having to compensate for their alien appearance can be rejected, as the parasitic chicks and host young are of the same size and appearance.