Natal dispersal is a key demographic process for evaluating the population rate of change, especially for long‐lived, highly mobile species. This process is largely unknown for reintroduced populations of endangered avian species. We evaluated natal dispersal distances (NDD) for male and female Whooping Cranes (Grus americana) introduced into two locations in central Wisconsin (Necedah National Wildlife Refuge, or NNWR, and the Eastern Rectangle, or ER) using a series of demographic, spatial, and life history‐related covariates. Data were analyzed using gamma regression models with a log‐link function and compared using Akaike information criterion corrected for small sample sizes (AICc). Whooping Cranes released in the ER dispersed 261% further than those released into NNWR, dispersal distance increased 4% for each additional nesting pair, decreased about 24% for males as compared to females, increased by 21% for inexperienced pairs, and decreased by 3% for each additional year of age. Natal philopatry, habitat availability or suitability, and competition for breeding territories may be influencing observed patterns of NDD. Whooping Cranes released in the ER may exhibit longer NDD due to fragmented habitat or conspecific attraction to established breeding pairs at NNWR. Additionally, sex‐biased dispersal may be increasing in this population as there are more individuals from different natal sites forming breeding pairs. As the population grows and continues to disperse, the drivers of NDD patterns may change based on individual or population behavior.
The Whooping Crane (Grus americana; WHCR) is a large, long-lived bird
endemic to North America. The remnant population migrates between
Aransas National Wildlife Refuge, USA, and Wood Buffalo National Park,
Canada (AWBP), and has recovered from a nadir of 15-16 birds in 1941 to
~540 birds in 2022. Two ongoing reintroduction efforts
in Louisiana and the Eastern Flyway together total ~150
birds. Evidence indicates the U.S. Fish and Wildlife Service (USFWS) is
strongly considering downlisting the species from an endangered to a
threatened status under the Endangered Species Act (ESA). We examined
the current status of the WHCR through the lens of ESA threat factors,
the USFWS’s Species Status Assessment (SSA) framework, and other avian
downlisting actions to determine if the action is biologically
warranted. Our research indicates that WHCRs are facing an
intensification of most threat drivers across populations and important
ranges. The AWBP is still relatively small compared to other crane
species and most birds of conservation concern. To date, only one avian
species has been downlisted from an endangered status with an estimated
population of <3,000 individuals. Representation in terms of
WHCRs historic genetic, geographic, and life history variation remains
limited. Also, the lack of spatial connectivity among populations,
reliance of the reintroduced populations on supplementation, and
continued habitat loss suggest that WHCR populations may not be
resilient to large stochastic disturbances. Given that reintroduced
populations are not self-sustaining, neither supplies true redundancy
for the AWBP. Proposed downlisting before recovery plan population
criteria have been met is objectively unwarranted and reflects USFWS
inconsistency across ESA actions. Only by incorporating basic
quantitative criteria and added oversight into ESA listing decisions can
we avoid an action as misguided as downlisting the Whooping Crane
without consideration of its recovery plan criteria or ostensibly its
population ecology.
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