Decision Rules for Egg-Color-Based Rejection by Two Cavity-Nesting Hosts of the Brown-Headed Cowbird
Document Type
Article
Publication Title
Journal of Experimental Biology
Publication Date
7-2023
Keywords
brood parasitism, color perception, decision-making, egg discrimination, recognition
Abstract
Hosts of obligate avian brood parasites often evolve defense mechanisms to avoid rearing unrelated young. One common defense is egg rejection, for which hosts often rely on eggshell color. Most research has assumed that hosts respond to perceived color differences between their own eggs and parasite eggs regardless of the particular color; however, recent experiments have found that many hosts respond more strongly to brown foreign eggs than to equally dissimilar blue eggs. Yet, none of these prior studies tested a brown-egg-laying species and, with only one exception, all were conducted in open nests where light levels are considered sufficient for effective color-based egg discrimination. Here, we explored how two cavity-nesting hosts of the parasitic brown-headed cowbird (Molothrus ater) – the blue-egg-laying eastern bluebird (Sialia sialis) and the brown-egg-laying house wren (Troglodytes aedon) – respond to experimental eggs painted six distinct colors ranging from blue to brown. Rejection responses of both hosts were best predicted by perceived differences in color between the model egg and their own eggs. Specifically, we found that house wrens preferentially rejected eggs bluer than their own eggs. However, although we found that bluebirds relied on perceived differences in color for their egg rejection decisions, further tests are needed to determine whether they preferentially rejected brown eggs or simply responded to absolute perceived differences in color. These findings demonstrate that these cavity-nesting birds treat perceived color differences in distinct ways, which has important implications on the coevolutionary arms races and the interpretation of avian-perceived color differences.
Funding Source
Work on house wrens was supported by a grant from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (R15HD076308) to S.K.S. and C.F.T. M.E.H. was supported by the Harley Jones Van Cleave Professorship at the University of Illinois.
Recommended Citation
Alexander J. Di Giovanni, Juliana Villa, Mark T. Stanback, Charles F. Thompson, Scott K. Sakaluk, Mark E. Hauber, Daniel Hanley; Decision rules for egg-color-based rejection by two cavity-nesting hosts of the brown-headed cowbird. J Exp Biol 15 July 2023; 226 (14): jeb245188. doi: https://doi.org/10.1242/jeb.245188
DOI
10.1242/jeb.245188
Comments
First published in Journal of Experimental Biology (2024):https://doi.org/10.1242/jeb.245188
Deposited in accordance with https://journals.biologists.com/jeb/pages/rights-permissions
The data and codes are available at figshare: http://doi.org/10.6084/m9.figshare.22215148.