More info for the terms:
crepuscular,
density,
ferns,
litter,
phaseDiurnal Activity: Snowshoe hares are crepuscular to nocturnal. They
are shy and secretive and spend most of the day in shallow depressions,
called forms, scraped out under clumps of ferns, brush thickets, and
downed piles of timber. They occasionally use the large burrows of
mountain beavers (Aplodontia rufa) as forms. Diurnal activity level
increases during the breeding season. Juveniles are usually more active
and less cautious than adults [
53].
Breeding Season: Snowshoe hares are active year-round. The breeding
season for hares is stimulated by new vegetation and varies with
latitude, location, and yearly events (such as weather conditions and
phase of showshoe hare population cycle) [
9,
35]. Breeding generally
begins in late December to January and lasts until July or August
[
35,
53]. In northwestern Oregon male peak breeding activity (as
determined by testes weight) occurs in May and is at the minimum in
November. In Ontario the peak is in May and in Newfoundland the peak is
in June. Female estrus begins in March in Newfoundland, Alberta, and
Maine, and in early April in Michigan and Colorado. First litters of
the year are born from mid-April to May [
9].
Gestation and Litter Size: The gestation period is 35 to 40 days; most
studies report 37days as the average length of gestation. Litters
average three to five leverets depending on latitude, elevation, and
phase of population cycle, ranging from one to seven [
9,
53]. Deep
snowpack increases the amount of upper-branch browse available to
snowshoe hares in winter and therefore has a positive relationship with
the nutritional status of breeding adults. Litters are usually smaller
in the southern sections of snowshoe hare range since there is less
snow. Newborn snowshoe hares are fully furred, open-eyed, and mobile.
They leave the natal form within a short time after birth, often within
24 hours. After leaving the birthplace siblings stay near each other
during the day, gathering once each evening to nurse [
9,
53]. Weaning
occurs at 25 to 28 days except for the last litter of the season which
may nurse for 2 months or longer [
64].
Pregnancy Rate and Productivity: Female snowshoe hares can become
pregnant anytime after the 35th day of gestation. The second litter can
therefore be conceived before the first litter is born (snowshoe hares
have twin uteri) [
9]. Pregnancy rates ranged from 78 to 100 percent for
females during the period of first litter production, 82 to 100 percent
for second litters, and for the periods of third and fourth litters
pregnancy rates vary with population cycle [
17]. In Newfoundland the
average number of litters per female per year ranged from 2.9 to 3.5,
and in Alberta the range was from 2.7 to 3.3 [
9]. The number of litters
per year varies with phase of population cycle (see below). In Alberta
the average number of litters per year was almost 3 just after a
population peak and 4 just after the population low [
17]. Females
normally first breed as 1-year-olds. Juvenile breeding is rare and has
only been observed in females from the first litter of the year and only
in years immediately following a low point in the population cycle [
9].
Mortality: In Yukon Territory 30-day survival of radio-tagged leverets
was 46 percent, 15 percent, and 43 percent for the first, second, and
third litter of the year, respectively. There were no differences in
mortality in plots with food added. The main proximate cause of
mortality was predation by small mammals including red squirrels
(Tamiasciurus hudsonicus) and arctic ground squirrels (Spermophilus
parryii). Littermates tended to live or die together more often than by
chance. Individual survival was negatively related to litter size and
positively related to body size at birth. Litter size is negatively
correlated with body size at birth [
57].
Population Cycles: Northern populations of snowshoe hares undergo
cycles that range from 7 to 17 years between population peaks. The
average time between peaks is approximately 10 years. The period of
abundance usually lasts for 2 to 5 years followed by a population
decline to lower numbers or local scarcity. Areas of great abundance
tend to be scattered [
36,
53]. Populations do not peak simultaneously in
all areas, although there is a great deal of synchronicity in northern
latitudes [
3]. From 1931 to 1948 the cycle was synchronized within 1 or
2 years over most of Canada and Alaska, despite differences in predators
and food supplies [
68]. In central Alberta low snowshoe hare density
occurred in 1965 with 42 to 74 snowshoe hares per 100 acres (40 ha).
The population peak occurred in November 1970 with 2,830 to 5,660
snowshoe hares per 100 acres (40 ha) [
44]. In the southern parts of its
range snowshoe hare populations do not fluctuate radically [
46].
Exclosure experiments in Alberta indicated that browsing by snowshoe
hares during population peaks has the greatest impact on palatable
species, thus further reducing the amount of available foods. In this
study there was insufficient nutritious young browse available to
sustain the number of snowshoe hares present in the peak years (1971 and
1972) in winter [
61].