OCTOBER 1989 - City of Boulder

NUTTALL'S COTTONTAIL
Sylvilagus nuttallii
Distribution.--The range of Nuttall's cottontail extends from the
Canadian border south to Arizona and New Mexico, and from the eastern
slopes of the Rocky Mountains west to the eastern slopes of the Cascade-
Sierra Nevada Range. It is found in suitable habitat throughout most of
the mountainous areas of Colorado from foothills to medium elevations.
Individuals have been documented throughout higher parts of Boulder County.
Description.--Sylvilagus nuttallii is relatively large for a cottontail
with long hind legs, comparatively short, round-tipped ears, a
long rostrum, and a large tail. It is dark pinkish and buffy above, with
a grayer, paler pelage on the sides and white underparts. Nuttall's
cottok~ail- is sy&atric with S . audubonii and is- distinguished by its
darker colored pelage with more zorsal black hairs; smaller ears with a
thin black line on the margin; a bright rusty nape; smaller hind feet,
and long dense hair covering the hind feet. Locally, S. nuttallii
may also be found in close .proximity to S. floridanus and-is separated
(with difficulty) by slightly paler dorsa pelage, duller brownish throat
patch, and more densely furred ears.
External measurements of four females from Garfield County were:
total length, 377 (367-397); tail, 40.2 (36-42); hindfoot, 97.2 (90-104);
ear, 64.0 (60-68). Greatest length of skull is around 70; zygomatic
breadth about 35. Average weight of six males from South Dakota was
809.5 g.
Natural History.--The species occurs at the edge of coniferous
forests and in dense stands of sagebrush or other brushy areas. It
ranges in elevation from 6000 feei (1800 m.) to 11,500 it. (3500 m.) in
the Pikes Peak region. Forms are used for cover. These are cup-like
cavities lined and covered with fur, grass, and small sticks. The cotton-.
tail is known to inhabit the abandoned burrows of other animals, but
burrowing behavior has not been well documented.
Foraging activity usually occurs in early morning, late afternoon and
evening, though this species may be active any time of the day or night.
Diet consists of sagebrush, juniper, and other shrubs. Grasses are a
preferred food in spring and summer.
Reproduction has not been detailed In colorado, but in Oregon, the
breeding season was reported from late February to late July. Gestation
is 28 to 30 days and females bear four or five litters per season. Litter
size .may vary from one to eight.
Cottontails are poorly known in Colorado, despite their abundance.
Perhaps this is partly because the species are so difficult to identify.
Nonetheless the Boulder Mountain Parks and adjacent greenbelt lands would
be an excellent place to study habitat relationships among these three
closely related species.
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Selected References,--Chapman et al. (1980) ; Jones et al. (in press).