Postfledging Habitat Associations of Mature Forest Birds with Early Successional Habitat in South-Central Indiana

Patrick J Ruhl, Purdue University

Abstract

In comparison to the nesting ecology of North American breeding birds, the postfledging period which occurs between nesting and fall migration is a poorly understood stage of avian life history. The postfledging period represents a critical stage for fledgling survival and nutrient acquisition for both fledglings and adults undergoing pre-basic molt preceding fall migration. During this time, many birds use habitat types that differ from their natal habitat; however, the specific factors driving postfledging habitat associations and foraging preferences remain unclear because birds are more cryptic, singing and moving less frequently in the postfledging period. Some birds that require mature forest habitat for nesting use early successional forest habitat during the postfledging period, but the habitat characteristics and trophic factors driving postfledging shifts in habitat preference are not well described. Optimal conservation of mature forest birds in Indiana, a state with a high degree of forest fragmentation, depends on a more complete understanding of postfledging ecology for multiple species. From 21 May – 18 August 2015 – 2017, I used a combination of constant effort mist-netting, radio-telemetry, nest-searching, and stable isotope techniques to characterize the postfledging associations of six mature forest bird species [Worm-eating Warbler (Helmitheros vermivorum), Ovenbird (Seiurus aurocapilla), Scarlet Tanager (Piranga olivaceai), Wood Thrush (Hylocichla mustelina), Red-eyed Vireo (Vireo olivaceus), and Black-and-white Warbler (Mniotilta varia)] in the Morgan Monroe and Yellowwood state forests in south-central Indiana. In 2016, the Worm-eating Warbler postfledging period was underway by 28 May, suggesting that postfledging habitat associations for some individuals may have persisted for ≥ 2 months. Radio-tagged female Worm-eating Warblers exhibited multiple strategies of habitat-use between individuals, and some females exhibited a roost preference for 8-year-old clearcuts. Habitat structure and food availability were both important predictors of mature forest bird captures during the postfledging period. Vegetation density was a significant predictor for five of the six focal mature forest species. Fruit availability was an important predictor of Scarlet Tanager and Wood Thrush captures, and invertebrate dry mass was a significant predictor for Worm-eating Warbler, Ovenbird, and Black-and-white Warbler captures. Stable isotope trophic analysis indicated that Worm-eating Warbler, Ovenbird, and Scarlet Tanager acted as generalist insectivores during the postfledging period. In addition, the two obligate insectivores (Worm-eating Warbler and Ovenbird) exhibited significant niche differentiation, suggesting that 8-year-old clearcuts provided adequate habitat to support the different foraging strategies and invertebrate preferences of both species during the postfledging period.

Degree

Ph.D.

Advisors

Dunning, Purdue University.

Subject Area

Wildlife Conservation|Ecology|Conservation biology|Behavioral Sciences|Physiology

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