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“Dead birds flying”: Can North American rehabilitated raptors released into the wild mitigate anthropogenic mortality?
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  • Christian Hagen,
  • John Goodell,
  • Brian Millsap,
  • Guthrie Zimmermann
Christian Hagen
Oregon State University

Corresponding Author:[email protected]

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John Goodell
Falconry Archives
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Brian Millsap
US Fish and Wildlife Service
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Guthrie Zimmermann
US Fish and Wildlife Service
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Abstract

As the human footprint expands to meet societal energy needs, as do the impacts to wildlife. Raptors in particular are highly susceptible to anthropogenic caused mortality. Industry sectors are encouraged to offset these causes of mortality. Several options to mitigate these losses have been proposed, including raptor rehabilitation. However, its role as a conservation tool is untested. Currently no peer-reviewed demographic analyses exists using post-release data from rehabilitated raptors to evaluate its effectiveness at continental scales. Our objectives were to estimate annual survival of rehabilitated and wild raptors, impute those estimates into demographic models to assess potential effects at individual and population levels. We hypothesized that rehabilitated raptors would survive similarly to their wild counterparts after an acclimation period, and that longer-lived species (K-selected) would benefit most from these releases. We used U.S. Geological Survey Bird Banding Lab band-recovery data (1974 – 2018) from 20 raptor species for modeling survival of rehabilitated individuals (n = 125,740) in comparison to wild birds (n = 1,913,352). Results from 17 species with adequate recovery data indicated that 5 species ≠ wild survival, 2 species had uncertain estimates, and 10 species ≈ wild survival by years 2 and 3 post-release. We acquired admissions (n = 69,707) and release (n = 25,740) data from 24 rehabilitation centers across the U.S. (2012-2021). We imputed survival, fecundity and numbers of releases into demographic models. These models quantified the extent to which rehabilitated raptors may contribute to broader conservation efforts, especially in the context of individual take. All but two species, had measurable numbers of individuals added to populations regardless of the number of releases. The general pattern was for K-selected species to yield larger benefits from rehabilitated supplementation to the population. Combined these results provide evidence that rehabilitation may serve as mitigation tool to offset incidental take