Oecologia

, Volume 184, Issue 2, pp 399–410

Rates of parasitism, but not allocation of egg resources, vary among and within hosts of a generalist avian brood parasite

  • Loren Merrill
  • Scott J. Chiavacci
  • Ryan T. Paitz
  • Thomas J. Benson
Behavioral ecology – original research

Abstract

Brown-headed cowbirds (Molothrus ater) deposit their eggs into the nests of other birds, which then raise the cowbird chick. Female cowbirds thus have limited options for impacting their offspring’s development via maternal effects compared to most other passerines. Cowbirds can impact their offspring’s phenotype by choosing among potential host nests, and by adjusting egg resources based on host characteristics. To examine whether cowbirds exhibit either or both of these strategies, we investigated rates of cowbird parasitism and egg investment (egg size, yolk-to-albumen ratio, and yolk testosterone and androstenedione) among and within host species in a shrubland bird community. We found that the probability of being parasitized by cowbirds, controlling for host status as a cowbird egg accepter or rejecter and ordinal date, varied significantly among host species, indicating an apparent preference for some hosts. Parasitism rates did not differ with host size, however, and despite variation in cowbird egg size among host species, this variation was not related to host size or cowbird preference. Among host species with eggs that are larger than those of the cowbird, cowbirds were significantly more likely to parasitize nests with relatively smaller eggs, whereas parasitism rates did not vary with relative egg size in host species with smaller eggs. There was no evidence for variation in cowbird egg components among or within host species. Our data indicate that cowbirds discriminate among host nests, but do not appear to adjust the composition of their eggs based on inter- or intraspecific host variation.

Keywords

Androgens Cowbird Maternal effects Parental investment Yolk 

Supplementary material

442_2017_3870_MOESM1_ESM.docx (25 kb)
Supplementary material 1 (DOCX 24 kb)

Copyright information

© Springer-Verlag Berlin Heidelberg 2017

Authors and Affiliations

  1. 1.Illinois Natural History Survey, Prairie Research InstituteUniversity of IllinoisChampaignUSA
  2. 2.School of Biological SciencesIllinois State UniversityNormalUSA

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