Evaluating the Canada lynx reintroduction programme in Colorado: patterns in mortality

Abstract

Summary 1. Reintroducing carnivores has become a widely used technique to restore the natural integrity of ecosystems. Accurate estimates of demographic parameters for reintroduced populations are essential to evaluate the success of the reintroduction programme, assess the need to release additional animals and to develop management recommendations. 2. In an effort to establish a viable population of Canada lynx Lynx canadensis in Colorado, USA, the Colorado Division of Wildlife released 218 wild-caught lynx from 1999 to 2006. All lynx were released with very high frequency (VHF) and/or satellite transmitters from which locations, mortality, reproduction, habitat use and movement patterns were documented. We present estimates of mortality. 3. Known-fate models could not be applied here to estimate mortality due to excessive missing location data because of either extensive movement outside of the study area or transmitter failure. Instead we employed a multistate model to address these issues. 4. We describe how the more general multistate mark–recapture model can accommodate missing data to estimate monthly mortality rates of released lynx both inside and outside the study area. We also explored factors possibly affecting lynx survival such as sex, time spent in pre-release captivity, movement patterns and origin. 5. Monthly mortality rate was lower inside the study area than outside, and slightly higher for males than for females, although 95% confidence intervals overlapped for sexes. Mortality was higher immediately after release [first month = 0·0368 (SE = 0·0140), and 0·1012 (SE = 0·0359) respectively, inside and outside the study area], and then decreased according to a quadratic trend. Annual survival was 0·9315 (SE = 0·0325) within the study area and 0·8219 (SE = 0·0744) outside the study area. 6. Synthesis and applications. For those contemplating lynx, or other carnivore reintroductions, we suggest identifying a high-quality release site to minimize mortality. We recommend that managers consider the demography of animals separately within and outside the reintroduction area for valid assessment of the reintroduction. Movements of reintroduced animals and their subsequent loss through death or permanent emigration may require the need for additional individuals to be released for a successful reintroduction effort.