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Spatio-temporal variation in age structure and abundance of the endangered snail kite: Pooling across regions masks a declining and aging population

PLoS ONE

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, , , and
https://doi.org/10.1371/journal.pone.0162690

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Abstract

While variation in age structure over time and space has long been considered important for population dynamics and conservation, reliable estimates of such spatio-temporal variation in age structure have been elusive for wild vertebrate populations. This limitation has arisen because of problems of imperfect detection, the potential for temporary emigration impacting assessments of age structure, and limited information on age. However, identifying patterns in age structure is important for making reliable predictions of both short- and long-term dynamics of populations of conservation concern. Using a multistate superpopulation estimator, we estimated region-specific abundance and age structure (the proportion of individuals within each age class) of a highly endangered population of snail kites for two separate regions in Florida over 17 years (1997–2013). We find that in the southern region of the snail kite—a region known to be critical for the long-term persistence of the species—the population has declined significantly since 1997, and during this time, it has increasingly become dominated by older snail kites (> 12 years old). In contrast, in the northern region—a region historically thought to serve primarily as drought refugia—the population has increased significantly since 2007 and age structure is more evenly distributed among age classes. Given that snail kites show senescence at approximately 13 years of age, where individuals suffer higher mortality rates and lower breeding rates, these results reveal an alarming trend for the southern region. Our work illustrates the importance of accounting for spatial structure when assessing changes in abundance and age distribution and the need for monitoring of age structure in imperiled species.

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Additional publication details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Spatio-temporal variation in age structure and abundance of the endangered snail kite: Pooling across regions masks a declining and aging population
Series title:
PLoS ONE
DOI:
10.1371/journal.pone.0162690
Volume:
11
Issue:
9
Year Published:
2016
Language:
English
Publisher:
PLOS ONE
Contributing office(s):
Coop Res Unit Seattle
Description:
e0162690; 18 p.
First page:
1
Last page:
18
Country:
United States
State:
Florida