LITTER PRODUCTION OF COASTAL NORTH CAROLINA MUSKRATS
Ry Kenneth A. Wilson
Game Management Specialist
North Carolina Wildlife Resources Commission
Litter production studies of the Virginia muskrat (Ondatra zibethica
macrodon) were made from 1951 to 195U as part of a study of its ecology
and management on the tidal marshes in Currituck and Dare counties, North
Carolina. The Virginia muskrat inhabits the Atlantic Coast from the upper
Delaware Bay to Pamlico Sound, North Carolina. Two color phases occur
throughout its range, a black and brown, the latter in most sites being
more abundant. During years of normal yields, Currituck County, center
of production in the State, produces about U0,000 muskrats; while in
Maryland, more than a million pelts have been harvested. Except for
work by Smith (1938) and Harris (1952) in Maryland, no other known litter
production studies have ever been made of this race of muskrats.
Since the early 19U0's, muskrat production in the tidal marshes of
North Carolina has decreased annually. According to fur dealers' reports,
trappers harvested about 50,000 muskrats from Currituck and Dare counties
in 19Ulj but in 195U, fewer than 20,000 pelts were taken. Harvest records,
kept by the writer for a 1,000-acre marsh owned by the Tice brothers on
northern Currituck Sound, show decreases in yields from 958 muskrats in
19U7 to 98 during 1951. Since then, no 'rat trapping has been done.
Similar population drops occurred on marsh even where there was little
or no trapping; namely, the l,26b-acre state-owned Northwest River Marsh —
one of the principal study areas in this investigation. Why muskrats
failed to increase under near refuge conditions remained an enigma. Food,
cover, and water were, in general, plentiful; and investigations disclosed
no epizootic. Finally, it was discovered that raccoon predation on litter
populations was the factor responsible for the sharp 4drop in muskrat pro¬
duction. Before this discovery, however, reproduction studies had started.
Since sterility was suspected, one of the main objectives of the investi¬
gation was to determine if muskrats were having young.
Breeding Season
Field investigations and weight and sex data obtained on about
12,000 muskrats since 19U7 have provided general information on the
breeding seasons of coastal muskrats. Uteri studies have also disclosed
important facts. The data from these sources indicate that, except dur¬
ing unusually cold winters, some breeding occurs during every month in
the year. Breeding activity is believed to be greatest during late win¬
ter and spring, usually from mid-February to mid-April, and some years
to early May. Mating subsides during hot weather in June and July, but
increases some from mid-August through September. Fall breeding appears
to be largely confined to young muskrats that have just attained sexual
maturity and a few prolific females.
In Maryland, Smith (1938) concluded that muskrats "breed every month
in the year, with the possible exception of November and December." He
found that most young are born from mid-April to mid-September. This in
