The effect of rearing methods on survival of reintroduced black-footed ferrets

We estimated minimum survival rates for 282 young-of-year, captive-reared, black-footed ferrets (Mustela nigripes) reintroduced into prairie dog (Cynomys spp.) colonies in Wyoming, Montana, and South Dakota. We used night surveys with spotlights to locate ferrets about 1 month and 9 months postrelease. We modeled minimum survival rates using gender, year, site, and 4 rearing methods. Minimum survival rates were highest (30% for 1 month, 20% for 9 months) for ferrets reared from early ages in outdoor pens with simulated prairie dog habitat; survival was lowest for cage-reared ferrets released without pen experience (11% for 1 month, 2% for 9 months). Rearing method and year influenced 1-month survival in a comparison of 3 levels of pen experience (pen rearing as defined above, transfer of kits from zoos to pen facilities at age 60-90 days, transfer at age >90 days) during releases in 1994-95 in Montana. Higher survival was associated with intensive management of coyotes (Canis latrans) in 1995. Survival was not different (P > 0.05) between sites or sexes, regardless of model. We recommend routine use of outdoor pens for prerelease conditioning of black-footed ferret kits.