Age-specific reproductive success and its contributing factors in the endangered golden-cheeked warbler

Jukkala, Gabriella L.

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https://hdl.handle.net/2142/117686 Copy

Description

Title

Age-specific reproductive success and its contributing factors in the endangered golden-cheeked warbler

Author(s)

Jukkala, Gabriella L.

Issue Date

2022-12-06

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

• Sperry, Jinelle H
• Ward, Michael P

Committee Member(s)

Stodola, Kirk W

Department of Study

Natural Res & Env Sci

Discipline

Natural Res & Env Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Setophaga chrysoparia
• Golden-cheeked Warbler
• age-related variation
• reproductive success
• nest survival
• time of nesting
• habitat
• nest attendance
• endangered species
• constraint hypothesis

Abstract

Reproductive success varies with age in most birds, yet patterns are often overlooked when managing endangered species despite their potential applications for recovery. Success is generally predicted to improve until middle-age before declining; however, obtaining sufficient sample sizes to detect this or other patterns is challenging for short-lived species. In addition, first-time (SY) breeders typically have lower success than all older (ASY) birds because they are less competent at certain factors, but the specific factors and their relative importance to reproductive success can vary considerably among species. I examined how age and its associated factors affected breeding performance of the endangered Golden-cheeked Warbler (Setophaga chrysoparia). I used long-term monitoring data to establish age-specific patterns of reproductive success. I also evaluated age- and sex-related variation in multiple factors that could potentially constrain the success of SY breeders. Finally, I used model selection to determine the primary factors driving age-specific reproductive success. Nest survival increased with male age from the SY to the 5Y age class. Overall, SY males were less successful than older males, as they were less likely to obtain a mate, paired less often with ASY females, had lower nest survival, and produced fewer fledglings. Age-related constraints occurred at multiple points in the breeding cycle. SY birds initiated nesting later and had shorter breeding seasons than ASY birds. Compared to their SY counterparts, ASY male nest sites had lower oak basal area and live oak density, and ASY female nest sites had steeper slopes and higher Texas oak density. However, there was no effect of age on clutch size, brood size, or productivity of successful nests. Date and nesting habitat were the primary factors driving nest survival. For both male ages, nest survival declined with increasing oak basal area, was highest early in the season, and varied non-linearly with date, but it declined earlier and more rapidly for SY males. My results indicated warblers experienced greater reproductive success with age primarily through improved nest predator avoidance achieved, specifically, by nesting earlier, for longer into the season, and in higher quality habitat. However, SY birds were capable of producing a similar number of young to ASY birds if their nests survived to fledging age; therefore, reducing nest predation for SY birds could contribute to population goals. Effective habitat management may improve SY nest survival, including increasing Ashe juniper recruitment in oak-dominated woodlands and maintaining a well-developed understory tree layer. Protecting mature juniper forests on slopes for breeding habitat is also critical for long-term population viability, as these areas were frequently used for nesting by older, earlier-nesting, and more successful breeders.

Graduation Semester

2022-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Gabriella L. Jukkala

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