Brown-and-yellow marshbirds reduce their acceptance threshold of mimetic brood parasite eggs in the presence of non-mimetic eggs

MERMOZ, MYRIAM E.; HAUPT, CAROLINA; FERNANDEZ, GUSTAVO J.

JOURNAL OF ETHOLOGY

SPRINGER TOKYO

Año: 2016 vol. 34 p. 65 - 71

0289-0771

The recognition andsubsequent rejection of brood parasite eggs is one of the most commonlyobserved defensive behaviors of the host. The brown-and-yellow marshbird ( Pseudoleistesvirescens ) is a common host of the shiny cowbird ( Molothrus bonariensis ).This host rec- ognizes and rejects immaculate white eggs of the cowbird, butaccepts this bird?s spotted eggs. We assessed the acceptance thresholdhypothesis which proposes that par- asite egg recognition is context-dependent.We experi- mentally parasitized host nests with a spotted cowbird egg andsimultaneously added: (1) one novel egg with spots similar to those of acowbird egg but on a blue background or (2) one immaculate white cowbird egg.In this setting, 78 % of the novel blue egg with spots and 77 % of the cowbird?simmaculate white eggs were quickly recognized and rejected. The rejectionfrequency of spotted cowbird eggs was also high (60 %) and was not related tothe type of egg which had been added to the host nest together with the spottedcowbird egg. This rejection frequency of spotted cowbird eggs is higher thanthe 21 % that we previously found in a similar experimental setting but in whichthe spotted cowbird egg was added singly to the host nest. These resultssupport the acceptance threshold hypothesis that predicts an adaptivemodulation of the antiparasite defence when the perceived risk of parasitism ishigh.