Pennsylvania Game News - January 2018 - 17

stream and shoreline plants have a tougher
time getting established.
Although minks are a muskrat's No.
1 predator, minks still will take whatever
comes easiest. So, if it's easier, or less
troublesome, to eat minnows, or frogs, a
mink might.
Minks do fancy muskrats, both young
and adults. And if opportunity knocks, or
the mink is feeding a litter, it might prefer
to tangle with a muskrat, incisors and all.
Muskrats are most vulnerable when
they're concentrated in shallow water, or
inhabiting shallow-water lodges or burrows, he added.
But even muskrats taken by predators are part of annual mortality, which
includes everything from trapping and
highway strikes to disease and extremeweather losses that seem to balance out
from year to year.
"A bump in the death rate from one
source tends to offset rates from other
mortality sources," Hardisky explained.
"That compensatory balancing usually
sustains a relatively consistent population."
But when habitat sours, muskrats sustain additional mortality that only habitat
improvement can reverse.

MUSKRAT MATURITY

JANUARY 2018

Jacob Dingel

Further complicating the muskrat's
chance to recover are changes in its age
structure, Hardisky said. Fewer adults are
surviving to reach breeding age.
"The proportion of adult muskrats in
the fall population has decreased from 23
percent in the early 1980s to 9 percent in
2016," Hardisky noted. "They're dying,
because there isn't sufficient habitat to
protect them."
Muskrats that reach adulthood have
learned how to stay one step ahead of
predators. But when they can't make it,

when there's no place to get away, the
breeding pool shrinks. Then, fewer young
muskrats augment the core population.
It's a bottleneck caused by inadequate
habitat, nature's way of emphasizing that
every habitat - good or bad - has a carrying capacity.
"Habitat stability is the key to muskrat
population stability," he emphasized.
Capable of dispersing up to 20 miles,
muskrats have always found a way to reenergize deflated populations, Hardisky
said. But they can't build a population
without sufficient food and cover, and
escape outlets.
Minks, however, are more opportunistic and adaptable. Although they're semiaquatic by nature, they're no strangers to
overland hunting, particularly in winter,
when aquatic prey availability wanes.
Any animal muskrat-sized or smaller is
fair game.
It's that adaptability that has helped
minks - otters and fishers, too - recolonize
their former range in the Commonwealth.
But coincidence also has helped minks.
As muskrat populations declined
through waterway rehabilitation, trapping pressure fell with them. Interest
in muskrat trapping is almost always
driven by large numbers of muskrats or
fur prices. But when both enticements
weaken considerably, muskrat trappers
put their traps away.
"The decrease in muskrat trapping
effort probably helped mink populations
increase and expand," Hardisky noted.
"Since minks and muskrats are trapped
simultaneously, less muskrat trapping
effort might have resulted in less mink
trapping effort."
Unlike muskrat populations, mink
populations show no sign of decline anywhere in Pennsylvania, Hardisky said,
even though some of their prey popula-

Pennsylvania Game News - January 2018

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