Long-term population trends of endangered Hawaiian waterbirds |
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Authors: | J Michael Reed Chris S Elphick Elena N Ieno Alain F Zuur |
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Institution: | (1) Department of Biology, Tufts University, Medford, MA 02155, USA;(2) Department of Ecology and Evolutionary Biology, Center for Conservation and Biodiversity, University of Connecticut, 75 North Eagleville Rd. U-3043, Storrs, CT 06269, USA;(3) Highlands Statistics, Ltd., 6 Laverock Rd., Newburgh, AB41 6AA, UK;(4) Oceanlab, University of Aberdeen, Main Street, Newburgh, AB41 6AA, UK |
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Abstract: | We analyzed long-term winter survey data (1956–2007) for three endangered waterbirds endemic to the Hawaiian Islands, the
Hawaiian moorhen (Gallinula chloropus sandvicensis), Hawaiian coot (Fulica alai), and Hawaiian stilt (Himantopus mexicanus knudseni). Time series were analyzed by species–island combinations using generalized additive models, with alternative models compared
using Akaike information criterion (AIC). The best model included three smoothers, one for each species. Our analyses show
that all three of the endangered Hawaiian waterbirds have increased in population size over the past three decades. The Hawaiian
moorhen increase has been slower in more recent years than earlier in the survey period, but Hawaiian coot and stilt numbers
still exhibit steep increases. The patterns of population size increase also varied by island, although this effect was less
influential than that between species. In contrast to earlier studies, we found no evidence that rainfall affects counts of
the target species. Significant population increases were found on islands where most wetland protection has occurred (Oahu,
Kauai), while weak or no increases were found on islands with few wetlands or less protection (Hawaii, Maui). Increased protection
and management, especially on Maui where potential is greatest, would likely result in continued population gains, increasing
the potential for meeting population recovery goals. |
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Keywords: | Endangered species Generalized additive models Management Recovery Time series Wetland |
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