Exploring the rules of egg rejection in the American robin through conjoint experimentation |
Devin J. Goodson1, Jeffery P. Hoover2, Abbigail Turner3, Carena J. van Riper4, Mark E. Hauber1,2,3,5. 1Program in Ecology, Evolution, and Conservation Biology, University of Illinois at Urbana-Champaign, Urbana, IL, United States; 2Illinois Natural History Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, Urbana, IL, United States; 3Department of Evolution, Ecology, and Behavior, School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, United States; 4Department of Natural Resources and Environmental Sciences, University of Illinois at Urbana-Champaign, , Urbana, IL, United States; 5Advanced Science Research Center and Program in Psychology, Graduate Center of the City University of New York, New York, NY, United States |
In this study we focus on the American robin (Turdus migratorius), a robust rejector of parasitic eggs laid in its nest by the brown-headed cowbird (Molothrus ater). Employing a randomized multiple simultaneous parasitism paradigm, we experimentally investigated how visual traits influence the rejection rates of eight distinct model eggs across 28 different pairings of two model eggs at a time. Utilizing a conjoint design analysis, we assessed egg-rejection decisions by evaluating how female robins made a choice to accept one egg while rejecting the other. Our findings reaffirmed the role of egg color, size, and maculation as key visual cues influencing model-egg rejection behavior in American robins. Specifically, we found that parasite-like white model eggs were 50% more likely to be rejected relative to robin-mimetic blue eggs, robin-sized model eggs were 39%��likely to be�accepted�compared to cowbird-sized eggs, and maculated eggs were 18% more likely to be rejected compared to immaculate eggs. These findings advance our knowledge of American robins' rejection behavior and showcase an innovative methodology for future research on bird decision-making. |