Abstract
Rothstein (Behavioral Ecology and Sociobiology, 11, 1982, 229) was one of the first comprehensive studies to examine how different egg features influence egg rejection behaviors of avian brood parasite–hosts. The methods and conclusions of Rothstein (1982) laid the foundation for subsequent experimental brood parasitism studies over the past thirty years, but its results have never been evaluated with replication. Here, we partially replicated Rothstein's (1982) experiments using parallel artificial model egg treatments to simulate cowbird (Molothrus ater) parasitism in American robin (Turdus migratorius) nests. We compared our data with those of Rothstein (1982) and confirmed most of its original findings: (1) robins reject model eggs that differ from the appearance of a natural robin egg toward that of a natural cowbird egg in background color, size, and maculation; (2) rejection responses were best predicted by model egg background color; and (3) model eggs differing by two or more features from natural robin eggs were more likely to be rejected than model eggs differing by one feature alone. In contrast with Rothstein's (1982) conclusion that American robin egg recognition is not specifically tuned toward rejection of brown‐headed cowbird eggs, we argue that our results and those of other recent studies of robin egg rejection suggest a discrimination bias toward rejection of cowbird eggs. Future work on egg recognition will benefit from utilizing a range of model eggs varying continuously in background color, maculation patterning, and size in combination with avian visual modeling, rather than using model eggs which vary only discretely.
Highlights
Reproducibility is a central concern of the modern scientific approach and paramount to research progress (Baker, 2016; Kelly, 2006; Nakagawa & Parker, 2015)
Through careful design of artificial model eggs constructed from plaster of Paris and painted with acrylic and latex paints, Rothstein (1982) separated the relative influences of egg size, background color, and spotting on robin and gray catbird egg rejection responses
Egg rejection behavior in robins likely evolved as a defense against brood parasitism by the mostly sympatric brown-headed cowbird (Molothrus ater; hereafter: cowbird), an obligate interspecific brood parasite (Abernathy & Peer, 2015; Briskie, Sealy, & Hobson, 1992; Croston & Hauber, 2014, 2015a; Friedmann, 1929; Kuehn, Peer, & Rothstein, 2014; Lang, Bollinger, & Peer, 2014; Rothstein, 1975a)
Summary
Reproducibility is a central concern of the modern scientific approach and paramount to research progress (Baker, 2016; Kelly, 2006; Nakagawa & Parker, 2015). We set out to replicate Rothstein’s (1982) experiments using a parallel set of artificial model eggs to reexamine the relative influence of discrete differences in model egg background color, maculation, and size on robin egg rejection decisions. We conducted a partial replication (for replication type definitions, see Kelly, 2006; Nakagawa & Parker, 2015) of Rothstein’s (1982) experimental methods, combined data from our experiments with those of Rothstein (1982), and analyzed which egg features predict robin egg rejection responses with an information-theoretic statistical approach using generalized linear mixed models (Bolker et al, 2009; Burnham & Anderson, 2002; Symonds & Moussalli, 2011)
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