UC Davis Natural Reserve System
Stebbins Cold Canyon Reserve
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Mammals of Cold Canyon
Most visitors to the Stebbins Cold Canyon Reserve may give little thought to the rich mammalian fauna that lives in the region. After all, most mammals are nocturnal and those that are generally active during the daylight hours are usually quite secretive, rarely showing themselves to we human visitors. However, it would be a serious mistake to dismiss the mammals just because they are less conspicuous than their avian neighbors. Ranging in size from the 1/4 ounce shrew to the large, lumbering black bear, over 40 species of mammals call this area home for much or all of their lives. Below are descriptions of the most common mammals of Cold Canyon. For a more complete list, look at the complete checklist.
Virginia oppossum (Didelphis virginiana).
The oppossum is the only marsupial of North America. Like all marsupials, it raises its
young in an abdominal pouch. This pouch may be the key to its abundance – an oppossum
can simultaneously have a batch of young developing in the pouch and an additional set on
its back, and thereby produce a huge number of young in its lifetime. Another key to its
abundance is its omnivorous habitats. The oppossum readily eats fruits, insects,
carcasses, and garbage, and these scavenging habits have made it a common city resident.
Observing an oppossum is difficult, as they are active only at night. If you are lucky
enough to stumble on one, you may witness its classic ability to play dead. In fact, the
oppossum is not playing – its immobility is caused by a fright reaction.
Racoon (Procyon lotor). A
characteristic dark mask and banded tail distinguish the ubiquitous raccoon. Racoons are
one of the most common carnivores, although their designation is a bit of misnomer as they
readily eat anything edible. Well-known for their ability to pry open garbage cans,
racoons will also feast on fruit or frogs, carrion or crayfish. Racoons seem particularly
attracted to water, which they happily play in and use to constantly clean their paws.
Observing these curious and clever mammals is difficult to do by day, for they are
primarily nocturnal.
Striped skunk (Mephitis mephitis). These primarily nocturnal scavengers
wander Cold Canyon in search of berries, insects, and dead animals. Their characteristic
black-and-white coloration generally warns most potential predators of their nauseating
spray, and as a result, skunks seem to bumble along their way without much concern for the
presence of predators.
Coyote (Canis latrans). The wily
coyote is a resident of Cold Canyon, but individuals are so secretive that few people get
even a glimpse of them. These mammals, about the size of a collie or a boxer, remain
hidden by day but roam the homestead trail by night, sometimes barking and yipping in a
caucaphonous chorus. They leave behind a few obvious signs of their presence: their
footprints (which are usually impossible to differentiate from the prints of other dogs)
and their scats. These scats attest to their varied diet of berries, seeds, and small
mammals.
Bobcat (Felis rufus). These cats are a
rare sight in Cold Canyon, but can be readily identified by their spotted coat, pointy
ears, and stubby tail. Bobcats are true carnivores, chasing down mice, rabbits, birds, and
snakes for their meals. Like all mammals, bobcats are primarily nocturnal, but are also
active in the mornings and late afternoons.
Mountain lion (Puma concolor).
Perhaps the most famous of California’s mammals, the mountain lion is also one of the
rarest. These large cats are active primarily at night, on the hunt for deer, rabbits, and
other mammals, but on occasion they have been seen in the early morning and even the
afternoon. By day, mountain lions generally retreat to the more remote parts of Wildhorse
and Cold Canyon. They are sometimes confused with bobcats, but their large thick tail and
uniformly tawny fur easily distinguish them from Cold Canyon’s other wild cat. The
sight of a mountain lion is lucky indeed, but if you do see one, act threatening, make a
lot of noise, and stand your ground to prevent the lion from treating you as potential
prey.
California ground squirrel (Spermophilus beecheyi). California ground
squirrels are mottled squirrels with dark blotches on their backs, and are one of the few
mammals that are active by day. Although they occasionally climb into trees to find food
or to sun themselves, they are most comfortable down near the ground, especially near
their burrows. The high-pitched alarm whistle of a California ground squirrel is often
mistaken for a bird call, especially because the squirrel
is rarely in sight after it
whistles. Ground squirrels have good reason to stay alert, for they are hunted by many
other vertebrates in Cold Canyon, including birds of prey, foxes, and rattlesnakes. Of
particular interest to some researchers at UC Davis are their interactions with
rattlesnake. Adult ground squirrels are immune to the venom of rattlesnakes, but their
young are not. In the presence of a rattlesnake, adult ground squirrels are particularly
aggressive, and often attempt to drive the snake away from its vulnerable young.
Deer mouse (Peromyscus maniculatus). These are the most common mammals on
the reserve, although their strictly nocturnal habits generally eliminate the possibility
of seeing
them. Deer mice have light brown fir on their backs, white fir on their bellies
and legs, long naked tails, and large eyes and ears. By night they forage for seeds and
berries, and will occasionally munch on insects. Deer mice are known to be carriers of the
Hantavirus, which recently caused human deaths in Arizona and eastern California. The
possibility of an outbreak in Cold Canyon is quite slim, for all outbreaks of the disease
involved prolonged human contact with mouse feces.
Dusky-footed woodrat
(Neotoma
fuscipes). Dusky- footed woodrats are the architects of the mammalian world. They live
in a complex structure built of sticks and other debris that can be up to eight feet in
height, and containing numerous tunnels and rooms. It is these houses that form the
nucleus for woodrat social life. Older, dominant individuals usually maintain control over
several houses. With the exception of a mother woodrat with young, woodrats live alone in
these houses. They shift from house to house, and occasionally move into new territory,
taking over a group of houses from an individual that has died or moved on. The presence
of many houses in an area is critical for the establishment of subadult woodrats
dispersing from their mother’s home.
Woodrats are generally nocturnal. They usually require some disturbance to or near their house to cause them to emerge from the house during the daylight. Skilled climbers, woodrats are often found moving through the branches of trees once night approaches, during which they forage for acorns, berries, seeds and other vegetable matter. When they are moving about on the ground, they are almost always found travelling on paths cleared of grass, twig, and rock obstacles.
California vole (Microus californicus). This small dark-gray mouse is most active by night, but may be heard at other times of the day as it travels along the runways it cuts through the grass. Voles can be distinguished from other mice by their short tails and hairy ears. They can be found wherever grass and other ground cover grows more than several inches high. Voles eat the grass, as well as seeds from many plants.
Brush rabbit (Sylvilagus bachmani). These small brown rabbits with white tails are sometimes flushed from thick grass and shrubs. Very likely they have a permanent shelter site nearby - a burrow, or a particularly tangled thicket – as they do not venture very far from safety. While they are active in the day, they are rarely conspicuous, for the brush rabbit is prey to a great many animals.
Mule deer (Odocoileus hemionus). Deer are plentiful in the Canyon, as
attested by their often-sighted footprints and scats, but their fear of human hunters
makes them a relatively uncommon sight. Deer often travel in small groups, and communicate
with each other by stamping their feet. The best place to see deer is along the creek near
the less accessible pools. Look for the trails that they use to travel from the hillslopes
to the pools.
Credits: All pictures except the woodrat image were obtained from Calphotos (http://galaxy.cs.berkeley.edu/photos/fauna/).The woodrat image was obtained from Ron Cole.
Last Updated 03/09/06