Abstract

The island fox (Urocyon littoralis) has experienced severe population declines since 1994. High neonatal losses during the first year of captive breeding on Santa Catalina Island raised significant concerns, but little was known about relative pregnancy success and neonatal loss in the wild population. We compared pregnancy rates and perinatal mortality in wild and captive island foxes during 2002 and 2003 to determine if pup losses in captivity exceeded those in the wild and to assess reproduction in animals released from the captive breeding program and translocated as part of population recovery efforts. In March 2002 and 2003, abdominal ultrasound examinations were performed on both captive and wild female island foxes to determine pregnancy status and fetal number. Wild pregnant foxes (n=8 in 2002; n=13 in 2003) were fitted with radiotelemetry collars to determine core use areas during denning. Pregnant captive females (n=5 in both 2002 and 2003) were monitored for comparison. Camera traps, visual observation and targeted trapping were used to determine the number of pups that survived to weaning in the wild. Video monitoring and visual observations were used to determine weaning success for captive animals. The adult pregnancy rate for wild foxes (95%) was significantly higher than for captive foxes (47.6%; p=0.003). Furthermore, perinatal mortality for both years combined was 43.2% for wild foxes and 15% for captive foxes (p=0.055). Average weaned litter size for both years was 1.8 pups for wild foxes and 1.9 pups for captive foxes, and average ultrasound fetal count for both years was 2.5 for wild foxes and 2.0 for captive foxes. Successful reproduction was documented in both translocated and captive-released individuals, and these individuals reproduced equivalently to wild foxes that had not been intensively managed. Since both pregnancy rates and perinatal mortality are lower in captivity than in the wild, captive breeding programs can increase their contribution to fox recovery by focusing efforts on increasing pregnancy rates while maintaining the successful postnatal husbandry methods currently employed. The use of camera traps to help assess pup survival was both a reliable and non-invasive method. Subsequent to this study, the Wildlife Health Center has employed camera traps to study river otters, mountain lions, and other species interactions in our ecosystem health investigations.