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Title: Examining the effects of behavior, landscape fragmentation,and climate change on avian distributions

Citation Type: Dissertation/Thesis

Publication Year: 2012

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Abstract: I examined the patterns and processes that determine Bobolink (Dolichonyx oryzivorus) distribution and abundance. First, Itested the hypothesis that visual openness could explain area sensitivity, the pattern of species being disproportionately absent from smallerhabitat patches. Icompared Bobolinkdensity and occupancy to a novel openness index, patch area, and edge effects. Our results supported a seasonally consistent openness threshold in occupancy (i.e. patches are either suitable or not). Once occupied, however, Ifound no relationships between patch openness or area and population density or measures of body condition (body mass, body size, circulating corticosterone levels). Despite individuals differing in response to simulated predators (flight initiation distance), differences were not related topatch area or openness. The openness response also was detected within fields, as bothBobolinksand Savannah Sparrows (Passerculus sandwichensis)placednests both away fromedges and in moreopen habitat when compared to expectations based on random placement. (Openness and edge were only moderately correlated.) However, Ifound no strong relationshipsbetween either openness or edges and reproductive success (numbers of eggs and fledglings, % of eggs producing fledglings, and nest survival), although there may be an openness effect on timing of reproduction (clutch completion date). Second, at the landscape scale, Ifound that climate and land use variables explained Bobolink distribution and abundance, but did a poor job of explaining the observed range shift in abundance from 1970-2008. Ipropose that some apparently area-sensitive species are actually responding to how open a habitat patch is, rather than to patch size.Our findings have implications for studies of area sensitivity, especially with regards to inconsistencies reported within species: specifically, (1) whether or not a study finds a species to be area sensitive may depend on whether small, open sites were sampled, and (2) area regressions were sensitive to observed densities at the largest sites, suggesting that variation in these fields could lead to inconsistent area sensitivity responses. Finally,our landscape results suggest that bioclimate models might do a poor job in predicting species range shifts due to climate change.

Url: https://dl.tufts.edu/pdfviewer/st74d304h/4m90f633b

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Authors: Keyel, Alexander, C

Institution: TUFTS UNIVERSITY

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Degree: Doctor of PhilosophyinBIOLOGY

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Pages: 180

Data Collections: IPUMS NHGIS

Topics: Natural Resource Management

Countries: United States