OCTOBER 1989 - City of Boulder

WESTERN EARVEST MOUSE
'Reithrodontomys megalotis
Distribution--The western harvest mouse has a wide distribution,
from California to recently invaded Indiana. The species occurs at
lower elevations throughout Colorado, on both sides' of the Divide.
It occurs in suitable habitat throughout the Boulder Mountain
Parks; museum specimens are available from Gregory Canyon.
Description--Harvest mice are distinguished from other mice by
the presence of grooved upper incisors. The animals are buffy above
and vary from dark buff to white beneath, vith prominent ears and a
tail that is as long as the head and body. They are distinguished from
the plains banrest mice by their externally larger size, a wider dorsal
caudal stripe, and larger cranial size.
Mean (and extreme) measurements of nine males and five females,
respectively, from the Big Thompson and South Platte river valleys
were: total length, 139.5 (136-1431,144.8 (141-152); tail, 66.7
(63-70), 70-2 (65-74); hindfoot, 17-7 (17-21), 16.5 (16-17); ear,
15.0 (13-17), 14.4 (13-16); weight, 14.19 (12.9-15.9), 16.08 (12-21);
greatest length of skull, 21.96 (21.7-22.5), 21.73 (21.1-22.4);
zygomatic breadth, 10.89 (10.7-11.1), 10.92 (10.7-11.2).
Natural History-Harvest mice are commonly associated with tall
vegetation and are very resilient to perturbation of their habitat.
They are found in rank vegetation of flood plains in disturbed situations.
They were found to be the most abundant smallmannnals in ungrazed sand
sage, grazed riparian, and ungrazed riparian ecosystems in revegetated
agricultural land in eastern Colorado. The animals build grass nests,
with one or more openings near the base on the surface of the ground,
in holes, on grass stems, or in small shrubs.
The diet consists of seeds, green plant parts, and some insects.
The animals are nocturnal and active year round. There are spring and
autumn molts.
Females are polyestrous, with occasional postpartum estrus known.
Reproductive activity commences in early spring and extends to late
autumn, with reduced activity ,during mid-summer. There are one to
seven young per litter, and there have been several litters per year
when bred in captivity. The young are altricial, and are weaned at 24
days. The aniaals live about one year. .
Owls, foxes, weasels , hawks, jays , skunks, and badgers are bown
to prey upon harvest mice. They have numerous parasites, including
ticks, mites, chiggers, lice, and fleas. The animals are commonly
associated with the house mouse, the meadow vole, and the prairie
vole.
Selected References--Webster and Jones (1982).
B..S.S.