Behavioral characteristics and hormonal mechanisms of egg ejection in the American robin (Turdus migratorius)

Turner, Abbigail May

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https://hdl.handle.net/2142/121981 Copy

Description

Title

Behavioral characteristics and hormonal mechanisms of egg ejection in the American robin (Turdus migratorius)

Author(s)

Turner, Abbigail May

Issue Date

2023-11-15

Director of Research (if dissertation) or Advisor (if thesis)

Anderson, Phil

Doctoral Committee Chair(s)

Anderson, Phil

Committee Member(s)

• Hauber, Mark E
• Ward , Michael P
• Fischer, Eva
• Hoover , Jeff
• Abolins-Abols, Mikus

Department of Study

Evolution Ecology Behavior

Discipline

Biology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• American robin
• egg rejection
• egg recognition
• Brown-headed cowbird

Abstract

Avian obligate brood parasites lay their eggs in other species nests, effectively releasing themselves from many of the behaviors related to raising their own offspring. This, in turn, imposes moderate to severe costs on hosts to raise the unrelated progeny. Some hosts of obligate brood parasites accept the parasitic egg(s); however, several host lineages have evolved defense behaviors to curb the costs associated with brood parasitism. One of these defense behaviors is the ejection (i.e., removal) of foreign eggs from the host’s nest. My dissertation focuses on the proximate cues, the behavioral characteristics, and endocrine mechanisms of anti-parasitic egg rejection in the American robin (Turdus migratorius), a well-known ejecter of parasitic brown-headed cowbird (Molothrus ater) eggs. First, I reviewed the previously published literature on the sensory cues that robins use (or do not) to eject foreign eggs from their nests. Visual cues such as background eggshell color and maculation are all important sensory cues utilized by robins to inform rejection decisions. Through my review, I identified under-studied sensory modalities and cues (i.e., tactile and odor cues) and then set out to experimentally test these. Through these studies I found a significant effect of tactile but not odor cues on robin egg rejection where rougher egg surfaces had higher rejection rates. The previous literature on robin egg rejection has largely focused on the egg rejection impact of the characteristics of the model egg(s) being added to experimental robin clutches. My remaining chapters, instead, aimed to understand the mechanisms and traits of this behavior more fully. We know little about how quickly and where (i.e., distance and direction taken) foreign eggs are deposited after the female has decided to remove it from the nest. Using a novel methodology of inserting radio-transmitters inside 3D printed model eggs, I examined the characteristics (i.e., latency, distance, and direction) of different colored model eggs ejected by the same female robins. I found egg color, but not female identity, to be a significant predictor of ejection latency while neither egg color nor female identity predicted the distance and direction ejected eggs were taken. Through further experimentation, however, I determined that female robins were not repeatable in where they deposited the egg but showed some consistency in how quickly they removed the egg and returning to the nest post-flushing when given the same model egg color repeatedly. Finally, I experimentally tested for the role of corticosterone, a glucocorticoid hormone often released in response to environmental stressors, in robin’s egg rejection behavior. Using a recently developed non-invasive method of corticosterone delivery, I found that experimentally increasing this glucocorticoid increased rejection rates of a model egg color that is typically rejected at intermediate rates. Taken together, the findings from these studies have significantly contributed and expanded our understanding of a well-studied anti-parasitic behavior in an avian host-brood parasite system.

Graduation Semester

2023-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Abbigail Turner

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