OCTOBER 1989 - City of Boulder

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DESERT COTTONTAIL
Sylvilagus audubonii
~istribution.--The desert cottontail occurs throughout the west from
the Canadian border to central Mexico and from central Nebraska to the
Pacific Coast. Locally, the species ranges through the plains of eastern
Colorado, including eastern Boulder County. The cottontail may be found
in the foothills or on arid mesas and creekbeds,
Description.--~k coat of the desert cottontail is short with sparsely
furred ears and slender hindfeet. The color is a pale grayish wash which
gets paler on the sides to a whitish belly. They also have an orangishbrown
throat and chest patch. S. floridanus and - S. nuttallii are both
close relatives,both are darker-dorsally.
External measurements of two males and mean (and extreme) of nine
females from Larimer County are : total length, 431, 448, 410.5 (392-438) ;
length of tail, 44, 46, 46.8 (35-56) ; hindfoot, 86, 98, 89.9 (83-100) ;
ear, 65, 75, 69.7 (59-88) ; weight, 1125, 985, 952,O gr. (609-1139) ; greatest
length of skull, 72-3, 68.6, 69.66 (67.9-74.1); zygomatic breadth, 34.8,
34.6, 35.23 (33.3-36.5)-
Natural History.--The habitat of desert cottontails is low elevation
deserts and semiarid grasslands, They prefer heavy brush and weedy field
margins. These cottontails do not normally burrow as they prefer protection
of thickets and rest in small, shallow. pear-shaped "forms". The animals
avoid the hot sun and feed in early morning and evening. The species is
active throughout the year and is generally solitary.
Grasses, forbs, .and shrubs especially succulent terminal shoots, com-
rpise the diet of desert cottontails.
Breeding patterns vary greatly depending on the warmth of the climate.
In Colorado, breeding can start as late as April and extend through August.
Females may have between one and five fitters per year with an average of
three. Litter size is generally three to four; embryos are reabsorbed if
the mother is frightened or if there are food shortages. The gestation
period is 28 days. The young are very altricial and about 90 mm long at
birth. Growth and development are very rapid, hovever, and the animals
are able to reproduce at about 90 days of age. Cottontails in the wild
usually live to be only about a year old.
Cottontails are connnon prey for many aerial and terestrial predators,
such as hawks, large owls, coyotes, fox, badger, bobcats, large snakes, dogs ,
and cats. They dso carq many parasites and are prone to rabies and tularemia.
They are also hunted extexnsivefy by man, IR Colorado, about
250,000 cottoneails are harvested annually, of which some 2000 are
taken in Boulder County.
Selected References.--Chapman
(in press) .
and Willner (1978) ; Jones et al.
K* M. K.