Release date influences first‐year site fidelity and survival in captive‐bred Vancouver Island marmots

Abstract

Maximizing survival in reintroduced, captive‐bred animals requires evaluation to identify best practices. This is particularly true for critically endangered species like the Vancouver Island marmot, endemic to British Columbia, Canada. From 2003 to 2010, 301 captive‐bred marmots were implanted with transmitters and released at extinct colony locations and other potentially preferred sites to bolster wild populations and establish new colonies. We evaluated release success based on three criteria: (1) site fidelity in the first summer, (2) survival to hibernation in fall, and (3) survival through winter. We used generalized linear mixed models and information theory to estimate the influence on release success of sex, age, and release practices, as well as local and landscape‐level habitat attributes. Our results suggest that overwinter survival most limited release success in the first‐year postrelease. In all years, overwinter survival was lower for newly released captive‐bred marmots than for wild or previously released marmots. Release date best predicted overall success, and was positively related to site fidelity and survival to hibernation but negatively related to overwinter survival. Our findings suggest that focused attempts to optimize release dates are likely to maximize long‐term reintroduction success.

Optimizing release strategies: a stepping‐stone approach to reintroduction

“…Consistent with release strategy studies comparing captive-bred with wild-born individuals (Letty et al, 2007), translocations of wild-born marmots from Mt Washington yielded the highest post-release survival rates. Sex and age effects on postrelease survival of marmots were consistent with Jackson et al (2016a), with greater survival for two-year-old marmots compared to other age classes, and females compared to males. Our analysis suggests that captive-bred marmots take 2 years to overcome release effects in Strathcona and reach annual survival probabilities comparable to those of wild-wild individuals.…”

“…For captive-wild marmots released at any age, Jackson et al (2016a) found 67% of newly released marmots hibernated within one km of their release site. Marmots released in July, like most marmots in this study, were less likely to be site-faithful than marmots released later in the summer, but earlier release dates were preferred because of improved overwinter survival (Jackson et al, 2016a). While we could not differentiate between mortality and permanent emigration from the study area, it is likely that most dispersing individuals do not locate a colony and are effectively lost to the population.…”

“…From 2003 to 2016, >490 captive-bred Vancouver Island marmots (hereafter marmots) were released into the wild, primarily into two metapopulations: the southern Nanaimo Lakes metapopulation (14 mountain colonies) and the northern Strathcona metapopulation (nine mountain colonies) on Vancouver Island (Vancouver Island Marmot Recovery Team, 2017). Released captive-bred marmots had greater mortality during their first wild hibernation which contributed to lower annual survival compared to resident wild-born marmots (Aaltonen et al, 2009;Jackson, Schuster & Arcese, 2016a). However, captive-bred marmots surviving their first hibernation had similar survival to wild-born individuals for subsequent over-winter periods (Jackson et al, 2016a) suggesting an acclimation period of 1 year.…”

“…In earlier years, marmots were released in either July or September (2011-2012; see Jackson et al, 2016a). In earlier years, marmots were released in either July or September (2011-2012; see Jackson et al, 2016a).…”

“…In 1997, conservation breeding for release was initiated. Released captive-bred marmots had greater mortality during their first wild hibernation which contributed to lower annual survival compared to resident wild-born marmots (Aaltonen et al, 2009;Jackson, Schuster & Arcese, 2016a). Released captive-bred marmots had greater mortality during their first wild hibernation which contributed to lower annual survival compared to resident wild-born marmots (Aaltonen et al, 2009;Jackson, Schuster & Arcese, 2016a).…”