Abstract
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.
Highlights
Reintroductions of individuals into currently uninhabited areas offer unique opportunities to learn about important demographic and social processes as populations become established, grow, and expand
We report natal dispersal distances (NDD) of Whooping Cranes in the Eastern Migratory Population (EMP) and compare them with those reported for other populations of Whooping Cranes and other crane species
We explore the potential relationship between NDD for Whooping Cranes in the reintroduced EMP and a variety of demographic, spatial, and life history variables that might help explain the observed pattern of natal dispersal
Summary
Reintroductions of individuals into currently uninhabited areas offer unique opportunities to learn about important demographic and social processes as populations become established, grow, and expand. In 2001, the Whooping Crane Eastern Partnership (hereafter, the Partnership) began reintroducing Whooping Cranes east of the Mississippi River to establish a population that summered in Wisconsin and wintered in Florida, USA. It is important to understand dispersal patterns and population range expansion for ongoing reintroductions of Whooping Cranes to direct habitat conservation efforts and inform release strategies for captive-reared cranes. We explore the potential relationship between NDD for Whooping Cranes in the reintroduced EMP and a variety of demographic (age, sex), spatial (number of nesting pairs, release area), and life history (rearing method, release method) variables that might help explain the observed pattern of natal dispersal. Small naturally occurring or reintroduced populations may exhibit a lack of sex-biased dispersal if individuals are coming from a single breeding area and one individual of each sex disperses to a breeding site and have equivalent NDD. We expect cranes that fly and those that spend more time in the area prior to release to have shorter NDD than cranes that spend little to no time at the release area or cannot fly prior to release
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