Following a spell of warm, spring-like weather, biologists at
the Vermont Fish & Wildlife Department observed black bears out
of their dens early in March. In recent years, mild weather has
frequently driven bears to enter their dens later and to emerge
"Bears are triggered to enter their den when food begins to
become scarce in fall or early winter, which usually follows a
heavy snowfall," said Forrest Hammond, bear project leader for
Vermont Fish & Wildlife. "Spring rains and warm
temperatures cause bears to leave their dens in search of uncovered
nuts and green shoots that start to emerge from the melting
snowpack. Bears will be active as long as they can easily find
food, but they will return to their dens if another deep snowfall
covers their food supply."
Shorter denning seasons in Vermont are consistent with reports
from the American West, Scandinavia and Spain, where many brown
bears have forgone hibernation altogether. Bears vary the
duration of winter dormancy based on their latitude and altitude;
bears that live further north or high in the mountains typically
den for a longer period of time.
Vermont's black bears are not the only species changing their
behavior due to recent winter weather patterns. Many bird species
have started to migrate, breed, and nest earlier in the spring in
John Buck, migratory bird project leader for Vermont Fish &
Wildlife, says that the department has observed state endangered
spruce grouse displaying courtship and breeding activity three
weeks early as a response to low spring snowpack levels in recent
years. "We're concerned that the females may nest early and
then see their nests buried under a heavy, late-season snowstorm,
which would likely result in a high rate of nest failures," he
The department has also observed that waterfowl are delaying
their departure from Vermont for the winter because they continue
to have access to open water, sometimes late into December or
Fish & Wildlife's Steve Parren has been studying a
population of wood turtles for the past 25 years. According to
Parren, the turtles have historically emerged from hibernation in
mid-April. "During the extreme warm spell that we had last
winter, we saw wood turtles basking on March 17, nearly a month
earlier than they are typically spotted," he said.
Other amphibian and reptile species responded to a warm
early-March rain this year by emerging from winter
dormancy. Herpetologist Jim Andrews, of the Vermont Reptile
and Amphibian Atlas, tracks the spring emergence of reptiles and
amphibians in Vermont. Andrews reported seeing spring peeper
frogs, spotted salamanders, and even some Eastern newts on March 12
this winter in the Champlain Valley.
Vermont's insects also vary their emergence dates based on the
spring temperatures. During warmer and drier springs, many
will emerge early.
"Flowering plants, bees, butterflies - these species have
evolved together based on a specific timing of events in the
spring," said Fish & Wildlife biologist Mark Ferguson.
"Many of the state's crops, including apple trees, require insects
for pollination." Last spring, many Vermont apple growers saw
high levels of frost damage when unusually high temperatures pushed
flower buds out before the last frosts of the season were over.
Milder winter temperatures can make controlling many forest pest
species difficult. Vermont's hemlocks are currently threatened
by a non-native insect known as the hemlock woolly adelgid, which
feeds on hemlock sap and may inject toxic saliva while
feeding. The adelgid's northward spread is limited by its
inability to tolerate long stretches of temperatures below -20
degrees Fahrenheit, which have become less frequent in Vermont in
the last decade.
As this pest spreads, it can cause devastating declines in
Vermont's hemlock forests. Hemlock forests are a critical
habitat for many Vermont species; bears, bobcats and ruffed grouse
all use hemlock for protective cover, and these forests are crucial
as wintering habitat for white-tailed deer. Following the mild
winter of 2011, hemlock woolly adelgid spread to seven additional
towns in Vermont, more than doubling the number of towns in which
the pest was previously detected.
While mild winters may benefit some species in Vermont, the
weather's unpredictability can prove difficult for wildlife.
Mid-winter rains followed by deep freezes or March temperatures
above 50 degrees Fahrenheit followed by heavy, late-season
snowfalls can cause onerous conditions for many species.
"During a normal winter, bud break, insect hatching and birds
returning to Vermont or establishing nests all occur at the same
time," added Buck. "Mild and unpredictable winters cause
these events to get out of sync. Birds that don't keep up
with changing weather patterns return to Vermont to nest and find
that the insects that they feed on have already hatched."
Photo by Tom Rogers, Vermont Fish & Wildlife