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The San
Joaquin Valley of California is a region of immense biological diversity,
and includes a number of endemic species and unique biotic communities.
California harbors more unique plants and animals than any other state, and
its biotic communities also face intense pressures. With the human
population of California increasing every year, there is always more and
more demand on the remaining habitat. Undeveloped habitat the size of San
Francisco is converted to residential or commercial use every six months.
The State of California lists 34 species of animals and 46 species of plants
as having been extirpated since the 1880s. The combined state and federal
lists of rare, threatened, or endangered plant and animal species in the
state totals 330, and there are more candidate species identified. One of
these listed species is the endangered San Joaquin kit fox.
Federal listed as Endangered and State listed as
Threatened
The kit
fox is the smallest canid species in North America and the San Joaquin kit
fox is the largest subspecies. It’s a small brown fox with a light colored
belly, and large ears. The San Joaquin kit fox was listed as endangered by
the U.S. Department of the Interior in 1967 and by the State of California
in 1971. The evolutionary and taxonomic relationships among small North
American foxes were recently examined and the conclusion was made that of
the traditional subspecies of the kit fox, the San Joaquin Valley population
is most distinct and should be considered a subspecies.
Early researchers
believed that by 1930 the range of the San Joaquin kit fox had been reduced
by half. They described the range prior to 1930 as including most of the
San Joaquin Valley from southern Kern County north to Tracy in San Joaquin
County on the west side of the Valley and up to La Grange in Stanislaus
County on the east side. No comprehensive survey of its entire historical
range has been completed, but local surveys, research projects, and
incidental sightings indicate that kit foxes currently inhabit larger areas
of suitable habitat on the San Joaquin Valley floor and in the surrounding
foothills of the coastal ranges, Sierra Nevada, and Tehachapi Mountains from
southern Kern County north to Contra Costa, Alameda, and San Joaquin
counties on the west, and near La Grange, Stanislaus County on the east side
of the Valley. Researchers also reported kit foxes occurring westward into
the interior coastal ranges in Monterey, San Benito, and Santa Clara
counties (Pajaro River Watershed), in the Salinas River watershed, Monterey
and San Luis Obispo counties, and in the upper Cuyama River watershed in
northern Ventura and Santa Barbara counties and southeastern San Luis Obispo
County. Another study conducted by the State of California found about 85
percent of the San Joaquin kit fox population in 1975 occurred within six
counties: Fresno, Kern, Kings, Monterey, San Luis Obispo, and Tulare. About
half the population could be found in Kern (41%) and San Luis Obispo (10%)
counties.
Kit fox mortality
results from many sources. Natural sources include predation, starvation,
drowning, and disease. Human induced factors include shooting, trapping,
poisoning, electrocution, collisions with vehicles, and suffocation. Loss
of habitat from urban, agricultural, and industrial development are the
principal factors in the decline of the San Joaquin kit since at least the
1950s. Researchers estimated that by 1958, 50 percent of the Valley’s
original natural communities had been destroyed. The completion of the
Central Valley Project and the State Water Project, that diverted and
imported new water supplies for agriculture, contributed to an estimated 34
percent loss of natural lands between 1959 and 1969 so that by 1979, only
about 7 percent of the San Joaquin Valley floor’s original wildlands south
of Stanislaus County remained untilled and undeveloped. Subpopulations of
the San Joaquin kit fox appear to be increasingly isolated from one another
due to other developments within its range including: cities, aqueducts,
irrigation canals, surface mining, road networks, petroleum fields, other
industrial projects, power lines, and wind farms. These actions singly and
cumulatively compress and constrict the San Joaquin kit fox into fragmented
areas, varying in size and quality. The isolation of subpopulations can
lead to increased rates of extinction due to the effects of inbreeding,
genetic drift, Allee effects, intra- and interspecific competition, and
catastrophic occurrences in the local environment.
Human actions or
natural disturbances that contribute to the fragmentation and subsequent
isolation of San Joaquin kit fox populations or their habitat have the
potential to move the species closer to extinction. Kit foxes have been
observed to disperse across disturbed habitats such as agricultural fields,
oil fields, rangelands, highways, and aqueducts, but maintaining movement
corridors to connect subpopulations remains an important goal of recovery
efforts for this species.
Interspecific
competition occurs between nonnative red foxes, coyotes and kit foxes.
Non-native red foxes may invade and occupy historic kit fox habitats,
compete for resources, and limit recovery efforts. Coyotes are highly
adaptable to disturbed environments and may out compete kit foxes for
available resources as well as kill them opportunistically. Predation by
large carnivores may account for the majority of the annual adult mortality
rate observed among San Joaquin kit fox in some areas. The coyote
population on the Naval Petroleum Reserves in California was reduced in an
attempt to enhance the kit fox population, but was ineffective.
The San Joaquin kit
fox is primarily nocturnal and typically occurs in annual grassland or mixed
shrub/grassland habitats throughout low, rolling hills and in the valleys.
The diet of kit foxes varies geographically, seasonally, and annually, but
throughout most of its range the diet consists primarily of kangaroo rats,
pocket mice, white-footed mice, San Joaquin antelope squirrels, California
ground squirrels, rabbits, black-tailed hares, ground nesting birds, and
insects.
Breeding occurs from
December through February with pups usually born in February or March. One
litter per year, with an average of four pups per litter, is typical. The
pups remain with the parents until June or July at which time the juveniles
usually disperse. Kit foxes may be solitary from mid-summer through late
fall and then occur in family groups from late fall through early summer.
The kit fox requires
underground dens for temperature regulation, shelter, reproduction, and
predator avoidance. Kit foxes commonly modify and use dens constructed by
other animals and human-made structures. Dens are usually located on
loose-textured soils on slopes less than 40 degrees, but the characteristic
of San Joaquin kit fox dens varies across the fox’s geographic range in
regard to the number of openings, shape, and the slope of the ground on
which they occur. Natal or maternal dens tend to be found on slopes of less
than six degrees. Kit foxes change dens often using numerous dens each
year. Monitoring the movement of foxes using radio telemetry portrayed that
foxes use individual dens for a median of 2 days before moving to a
different den. Avoidance of coyotes has been provided as a probable
hypothesis to explain this frequent change of dens. Researchers have
reported individual foxes using more than 20 den sites annually and family
groups using as many as 43. In another study, a single animal used 70
different dens over a two-year period.
The recovery
strategy for the San Joaquin kit fox focuses on the collection of data on
the distribution and status of the fox throughout its range. Other areas of
focus include: demographic information for foxes occupying natural,
agricultural, residential, and industrial lands; relations between prey
populations and kit fox population dynamics; interspecific interactions
between kit foxes and other native and non-native carnivores; and the direct
and indirect relations between land use practices and kit fox survival and
reproductive success.
written by: Howard
Clark, wildlife biologist, Fresno, CA. |
