Thanks to many years of careful planning and habitat restoration, several species including Black footed ferrets, California condors, Grey wolves, Musk ox, Golden eagles and Northern river otters have been or are being reintroduced into areas of their range where historic populations have disappeared or greatly diminished due to pressure from various human activities. The challenges of reintroduction are complex but the goal is always to eventually rebuild a stable, healthy, self-sustaining, diverse, population in areas protected from further human pressures.
Unfortunately for the animals involved, reintroduction to a new area requires capture, either from the wild in another part of the species range or from captive breeding populations, and relocation often over hundreds or thousands of miles. Acute stress upon the captured individuals is all but unavoidable in these sorts of situations, but most wild animals recover quickly from isolated acute stress events with little or no impact on their overall health. However, repeated or sustained chronic stress can have serious health impacts including increased susceptibility to disease and reduced growth rates and certainly impact the success of individual after their release. To avoid the negative consequences of chronic stress captive raised animals frequently undergo a process of habituation prior to release learning to successfully navigate, feed and protect themselves in a manufactured environment that is a similar to their final release situation as is feasible. For example prior to reintroduction, captive bred black-footed ferrets are housed in enclosures that allow them to learn to burrow, and hunt live prey – both skills that will be vital in the wild.
For animals that will be captured from the wild in one area and relocated to a different part of their historic range, the considerations are different. These animals can already have the skills and knowledge to survive in the wild, but they will be undergoing probably the single most stressful period in their lives as they are captured, transported and released. One option is to simply carry out the capture, relocation and release as quickly as possible, hopefully combining the process into a single acute stress event – intense but short. This is feasible if you’re talking about transporting a fish species on the far side of a dam, or a few miles for release into a nearby lake, but it is more difficult if you are talking about animals that will need to be transported over hundreds of miles. A recent study of river otters, captured in Washington state for release in New Mexico, examined fecal corticosterone levels to assess the stress levels of individual animals as a result of the “transport” part of the process. In this case, because of the transport distances involved, otters were captured in the wild and then held in captivity for 5-21 days prior to transport in dog crates by pickup truck and small plane. After arriving in New Mexico they were held in open pens at the release site for several days to acclimate prior to release. Fecal samples, collected both prior to transport and from the holding pens immediately after the animals were released, were dehydrated and stored at -80°C until assay. Corticosterone levels in each fecal sample were determined using the Arbor Assays DetectX Corticosterone EIA kit. Results showed that the initial samples collected prior to transport had on average 39.3% higher corticosterone levels than those collected at the release site. This suggests that although transport itself was almost certainly a stressful event, the short time period (~ 60 hours on average) that the otters were held at the release site prior to release was sufficient for corticosterone levels to drop. This suggests that the animals were not experiencing chronic stress and that the capture/transport/release protocol used should not negatively impact the survival of the animals in their new location.
Although the scientists and wildlife management experts involved in planning the reintroduction of native species plan carefully and work hard to limit stress placed on the animals in their care. It is also helpful to quantitate stress markers during the process to further understand the animals’ response and be able to make adjustments to the protocol for future reintroductions if necessary.