Is timing everything? Examining the importance of the timing of parasitism to cowbird reproductive success

Boldrick, Julia

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https://hdl.handle.net/2142/129299 Copy

Description

Title

Is timing everything? Examining the importance of the timing of parasitism to cowbird reproductive success

Author(s)

Boldrick, Julia

Issue Date

2025-05-06

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

• Schelsky, Wendy
• Hoover, Jeffrey P

Committee Member(s)

• Ward, Michael P
• Hauber, Mark E

Department of Study

Natural Res & Env Sci

Discipline

Natural Res & Env Sciences

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• brood parasitism
• behavior
• bird
• cowbird
• breeding behavior
• avian biology
• avian ecology
• parasitism

Abstract

Brood parasitism is a reproductive strategy where a parasitic parent leaves its offspring to be raised by an unrelated host. This has resulted in specialized adaptive behaviors selected to optimize the success of their progeny. The timing of when to leave a propagule with a host can be paramount to parasite success, and erring in this decision could have dire fitness consequences that strongly select for accurate parasitism timing. Brown-headed cowbirds (Molothrus ater) are North America’s most widespread avian brood parasite and successfully parasitize 170+ host species, but female cowbirds are cryptic and difficult to monitor, and much of how they make parasitism decisions is not well understood. Despite such diversity in hosts, cowbirds nearly always parasitize nests during the narrow window of the host’s egg-laying period before the start of incubation, resulting in their offspring typically hatching before the host’s. How important is it to get this timing right, and are there reproductive costs to parasitizing nests “late” (i.e., after the onset of host incubation)? I simulated three different parasite timing decisions by adding cowbird eggs to the nests of a common host, the prothonotary warbler (Protonotaria citrea), at different stages of the host’s laying and incubation period and monitored the effects on cowbird hatching success, hatching asynchrony relative to host eggs, and nestling size, health, and survival. I found that late egg placement produced cowbird nestlings that hatched at the same time or later than their host nestmates, resulting in smaller body size and markedly lower survival than those placed in the pre-incubation window, suggesting that accurate parasitism timing is an essential and likely strongly selected for behavior in brood parasites.

Graduation Semester

2025-05

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/129299

Copyright and License Information

Copyright 2025 Julia Boldrick

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