Habitat selection and survival of juvenile black-capped vireos during the post-fledging period

Dittmar, Erika

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Description

Title

Habitat selection and survival of juvenile black-capped vireos during the post-fledging period

Author(s)

Dittmar, Erika

Issue Date

2014-09-16

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

• Weatherhead, Patrick J.
• Sperry, Jinelle H.

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

Date of Ingest

2014-09-16T17:26:04Z

Keyword(s)

• Black-capped Vireo
• Vireo atricapilla
• post-breeding
• habitat selection
• survival

Abstract

Population declines of many species of songbirds have stimulated much research on breeding, migration, and wintering ecology. Until recently, the post-breeding season, the period from the completion of breeding and the onset of migration, has been overlooked. During this period, juvenile birds independent of parental care must find food to build up fat reserves for migration and simultaneously avoid predators. Many studies have reported low survival rates for juveniles as well as a shift in habitat selection during this time. If differences in ecological requirements result in juvenile birds using different habitats from breeding birds, then both breeding and post-breeding habitats need to be considered when managing species. Additionally, knowing how juvenile survival varies by age and sex is central to understanding population dynamics. My thesis examines habitat selection and survival of juvenile black-capped vireos (Vireo atricapilla) following their independence from parental care, from 2010-2013 in central Texas. The black-capped vireo is a federally endangered migratory songbird that nests almost exclusively in shrub vegetation, but previous anecdotal observations suggest that juvenile vireos may move to riparian areas once reaching independence from parental care. In chapter 1, I used mist-net capture rates and radio-telemetry to determine the relative abundance of juvenile vireos across habitats and to quantify habitat selection. Further, I investigated how vegetation density and arthropod abundance influenced habitat selection by juvenile vireos. I captured juveniles at similar rates in shrub and riparian vegetation; however, radio telemetry data indicated that juveniles selected riparian vegetation over most other available vegetation types. Juveniles chose areas characterized by more canopy cover, denser foliage, and more arthropods than at random. Riparian vegetation provides this combination of features more than other vegetation types, suggesting that cover and food are the basis for habitat selection by juveniles. My results suggest that habitat conservation strategies for black-capped vireos should include protection of riparian vegetation near breeding areas, and more generally, avian conservation strategies that focus only on breeding areas may potentially overlook other key habitats used by juveniles. Knowing how survival varies by age is central to understanding population dynamics. Nearly all of the studies to date concerning juvenile bird survival have focused on the dependent period, between when juveniles leave the nest and the termination of parental care. Still relatively unstudied is survival during the period when juveniles are independent of parental care. In chapter 2, I used radio telemetry data to estimate survival rates of juvenile male and female black-capped vireos during the period following parental care. Additionally, I used behavioral observations to investigate how movement patterns, vocalizations, and associations varied by sex. I followed the fates of 71 juveniles and, using known-fate models in Program MARK, estimated overall post-fledging survival to be 55% (86% for females and 40% for males). Movement patterns varied among individuals and males tended to make more foray movements than females. Both sexes were frequently seen in association with conspecifics and heterospecifics. Half of the males we tracked were observed singing, both sexes were observed making many types of vocalizations, and frequency of vocalizations did not vary between sexes. My findings highlight the importance of age and sex-biased survival rates for population dynamics. Having accurate estimates of juvenile survival may assist biologists in predicting population estimates and help determine future management plans.

Graduation Semester

2014-08

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Copyright 2014 Erika Dittmar

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