Using pregnancy rates and perinatal mortality to evaluate the success of recovery strategies for endangered island foxes

Abstract

Abstract Following a dramatic population decline in 1999, captive‐breeding and translocation programs were initiated to recover the Santa Catalina Island fox Urocyon littoralis . Neonatal losses during the first year of captive breeding raised concerns, but little information was available on which to base reproductive expectations in captivity, and pregnancy rates and pup mortality had not been assessed in free‐ranging foxes. In 2002 and 2003 we evaluated the relative contributions of captive breeding and translocation to population recovery by comparing pregnancy rates and perinatal mortality in free‐ranging and captive Santa Catalina Island foxes, and by comparing pregnancy rates and perinatal mortality were also compared between resident free‐ranging foxes and foxes that had been captive bred and released, or translocated as juveniles. Pregnancy rates and fetal number were determined using ultrasound. Free‐ranging pregnant foxes were followed via radiotelemetry, and a combination of camera‐traps, observation and targeted trapping was used to determine how many pups survived to weaning. Video cameras and observations were used to determine the weaning success for captive foxes. The adult pregnancy rate for free‐ranging foxes (95.0%) was higher than for adult captive foxes (47.6%; P =0.003). Perinatal mortality for pups born to free‐ranging mothers (43.2%) was higher than for pups born to captive mothers (15.0%, P =0.055). Adult pregnancy rates and perinatal mortality were 100 and 25.0% for translocated and captive‐bred foxes combined, and 92.3 and 53.6% for resident wild foxes. The average weaned litter size (±standard deviation) for free‐ranging foxes (1.8±0.6) was similar to that for captive foxes (2.1±0.4). Successful pup production by translocated and captive‐bred foxes supports the utility of these strategies to recover island foxes. Our approach, integrating veterinary and field biology techniques to assess the contributions of different management strategies to population recovery, can be utilized for other endangered species.