Aaltonen K, Bryant A, Hostetler J, Oli M. 2009. Reintroducing endangered Vancouver Island marmots: Survival and cause-specific mortality rates of captive-born versus wild-born individuals. Biological Conservation. 142: 2181-2190.
The Vancouver Island marmot is a small rodent that is only found on Vancouver Island and is listed as critically endangered. In 2004, there were thought to be only 35 marmots left in the wild. The proposed main reasons for the dramatic drop in numbers of this species are clearcut logging and increased predation. The decreased population size, limited habitat, and small distribution also make this species particularly vulnerable to extinction.
Captive breeding and release programs for this species began in 1997 to attempt to restore population numbers on the island. Some success was observed but in many cases, captive-bred animals had poor survival rates compared to wild marmots. It was not known why these released marmots were dying easier than wild animals. Perhaps the captive-bred individuals were worse at avoiding being eaten because of being raised in the absence of predators. Maybe these individuals had differences in body condition from the wild marmots. In any case, recovery programs could be more successful if the decreased survival rates and causes of death of captive-bred marmots are understood. This understanding could allow for new techniques to be implemented, such as raising and releasing captive marmots in a different way that could increase their survival and reproductive success.
The goal of the research summarized here was to examine the survival and causes of death of Vancouver Island marmots (both captive-bred and wild) using radio-telemetry data. The researchers hypothesized that wild marmots would be more likely to survive than captive-bred marmots and that older captive-bred individuals would have a greater probability of survival than young captive-bred marmots when they were eventually released into the wild.
Several significant results were found after analyzing the radio-telemetry data in this study. One major finding showed that, as hypothesized, wild marmots had a higher survival rate than captive-bred individuals. Figure 4 below illustrates this result. Second, captive-bred marmots were preyed upon more by eagles and cougars. They were also less likely to survive the winter (Figure 5). A third result which was consistent with an original hypothesis showed that older marmots were more likely to survive than pups (Figure 6a). Finally, marmots appeared to survive better in natural habitat types compared to clearcut habitats (Figure 6b).
These findings could be used to improve conservation efforts and successes of releasing captive-bred Vancouver Island marmots into the wild. For example, because the researchers found that captive-bred marmots survived better when they were released at two years of age or older, it may be beneficial to restrict releases to individuals of these ages in order to increase population numbers. Another consideration is that captive-bred individuals appeared to be killed more by eagles, and exposing marmots to eagles before their release may train them to be wary of these predators. It also seems important to preserve natural habitats as clearcut areas were found to decrease survival. Overall, these findings stress that studies such as this one are crucial in understanding and effectively conserving endangered species.
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