Stable-hydrogen isotope measures of natal dispersal reflect observed population declines in a threatened migratory songbird
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Author/Creator ORCID
Date
2012-06-09
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Citation of Original Publication
Colin E. Studds, Kent P. McFarland, Stable‐hydrogen isotope measures of natal dispersal reflect observed population declines in a threatened migratory songbird, (Diversity Distrib.)(2012)18, 919–930, https://doi.org/10.1111/j.1472-4642.2012.00931.x
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
Public Domain Mark 1.0
Abstract
Aim
Measuring dispersal is crucial for estimating demographic rates that inform conservation plans for rare and threatened species. We evaluated natal dispersal patterns in Bicknell's thrush (Catharus bicknelli) across most of the breeding range using a 10‐year data set of stable‐hydrogen isotope ratios in feathers (δ²HF) grown on the natal area and sampled 1 year later at the first breeding site.
Location
North‐eastern United States and south‐eastern Canada.
Methods
We used δ²HF values of adult thrushes sampled at 25 breeding sites as prior information for assigning first‐time breeders to their natal site. We calculated the minimum distance birds moved from their natal to first breeding site and fit these data to three statistical distributions for characterizing the importance of long‐distance dispersal: the exponential, Weibull and half‐Cauchy. Finally, we assessed differences in the probability of dispersal across the breeding range and through time to understand spatio‐temporal variation in demographic connectivity.
Results
The δ²HF values of first‐time breeders were lower compared with those of adults, a difference that was greater at the southern compared with northern breeding range extreme. Assignment tests accounting for age differences in δ²HF suggested that most birds dispersed < 200 km from their natal area and within the centre of the breeding range, whereas comparatively few individuals dispersed up to 700 km. A Weibull distribution provided the best fit to these data. Two of three corrections for age differences in δ²HF indicated that natal dispersal probability declined by 30–38% from 1996 to 2005.
Main conclusions
Our findings suggest that estimating natal dispersal with δ²HF measurements may contribute to understanding the resilience of geographically isolated Bicknell's thrush populations. Declining natal dispersal may be symptomatic of observed population declines and could compound this trend by limiting demographic exchange between habitat patches predicted to be increasingly isolated by natural and anthropogenic habitat changes.