Department or Program

Environmental Studies


Avian brood parasites lay eggs in other bird’s nests in order to avoid reproductive costs associated with incubation and chick rearing. Some hosts respond to parasitism by identifying and rejecting parasitic eggs from the nest. This rejection behavior may have evolved from nest sanitation practices, which are a set of cleaning behaviors that increase fledgling success and improve reproductive efficiency. Here, we use colonial-nesting American herring gulls (Larus smithsonianus) to test whether performing an act of nest sanitation increases the likelihood of rejecting a parasitic egg. First, we tested how the physical factors of an object affect frequency of rejection by experimentally placing objects varying in size, color, and shape into gull nests. Rejection rates were highest for small red wood chips and lowest for large egg-shaped objects. Based on these results, we designed an experimental test of the Nest Sanitation Hypothesis by examining whether the performance of sanitation behavior primes the rejection of a non-mimetic parasitic egg. Nests in the control group received only a non-mimetic egg, while experimental nests simultaneously received a non-mimetic egg and a debris item that had a 90% rejection rate in Experiment 1. We did not find data to support the Nest Sanitation hypothesis, as there was no significant difference in non-mimetic egg rejection between experimental and control groups. In supporting analyses, clutch size did not affect rejection, though the presence of a gull at the nest at time of experimental parasitism did increase the likelihood of egg rejection. The lack of evidence for a priming effect suggests that nest sanitation behaviors are not associated with the rejection of parasitic eggs in the American herring gull, and therefore nest sanitation may not be a pre-adaptation to parasitic egg rejection.

Level of Access

Restricted: Embargoed [Open Access After Expiration]

First Advisor

Donald Dearborn

Date of Graduation


Degree Name

Bachelor of Arts

Number of Pages



Available to all on Saturday, December 06, 2025