Pregnancy Rates and Pup Mortality in Island
Foxes (Urocyon littoralis) on Santa Catalina Island
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Dr. Deana Fritcher is holding a radio-collared
female island fox near the town of Two Harbors. This fox successfully raised
2 pups in 2002. Photo courtesy of Wildlife Health Center, 2002. |
Deana Fritcher, DVM, MPVM
Wildlife Health Center
One Shields Avenue
University of California
Davis, CA 95616
Project Collaborators:
Institute for Wildlife Studies
Santa Catalina Island Conservancy
The island fox (Urocyon littoralis) is only found on the California
Channel Islands. Island foxes are distributed as six genetically distinct subspecies,
one on each of the six largest Channel Islands. Four of the six island fox subspecies
have declined by as much as 95% since 1994, resulting in critically low population
sizes on four islands. This precipitous decline resulted in the island fox being
listed as critically endangered by the International Union for Conservation of
Nature. The island fox is also a candidate for federal endangered species listing.
In an attempt to safeguard remaining foxes and augment natural reproduction,
the entire wild populations of San Miguel and Santa Rosa islands and a portion
of the populations of Santa Catalina and Santa Cruz islands were placed into
captive breeding programs.
Low reproduction is a threat to island fox population recovery. High pup losses
during the first year of captive breeding on Santa Catalina Island were a significant
concern, but little was known about pregnancy and pup losses in the wild. Average
island fox litter size (1.5-2.1 pups) is very small compared to other wild canids.
Basic reproductive data regarding pregnancy rates and pup mortality in wild foxes
is needed to enhance the success of captive breeding and to better manage wild
fox populations.
In this study we compared pregnancy rates and pup mortality in wild and captive
foxes during 2002 and 2003 to determine if pup losses in captivity exceeded those
in the wild, and to assess reproduction in foxes released from the Catalina Island
captive breeding program and translocated as part of population recovery efforts.
Abdominal ultrasound examinations were performed on both captive and wild female
island foxes to determine pregnancy status and count the number of fetuses for
pregnant foxes. Wild pregnant foxes were fitted with radio telemetry collars
to determine their core use areas during denning, while pregnant females at the
Santa Catalina Island captive breeding facility were monitored using infrared
den box cameras for comparison. Self-triggered heat and motion sensitive cameras,
visual observations and targeted trapping were used to determine the number of
pups that survived to weaning for each wild female.
Our initial results suggest that more pups survive to weaning in captivity
than in the wild, but that pregnancy rates are lower in captivity. Also we showed
that island foxes born and raised in captivity can successfully reproduce in
the wild. These findings are encouraging and indicate that management efforts
have dramatically reduced pup mortality at the Catalina captive breeding facility,
and that island foxes raised in captivity are capable of mating and reproducing
in the wild. We hope this project will increase our knowledge of island fox reproductive
biology, which is beneficial for managing wild foxes and encouraging population
recovery. Results from this study are applicable to wildlife managers not only
on Santa Catalina Island, but also on the three Northern Channel islands with
captive breeding programs that have yet to release island foxes back into the
wild.
For further information regarding island fox health research or other research
programs of the Wildlife Health Center, please visit our website: www.vetmed.ucdavis.edu/whc.
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