influence du climat et de la prédation sur l'utilisation de l'habitat et la ...

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Beschta 2004). Predation rates were high on porcupines du ring the two years of study and
predation on adults was linked to the presence of snow covering the ground (chap. 3). We
observed porcupines reducing the time spent outside of the den and the duration of activity
bouts when snow penetrability increased. We suggest porcupines lowered exposure to
predators by reducing the time spent outside of the den when snow penetrability, and
therefore predation risk, was high.
Besides reducing the time spent outside of the den, porcupines also became more diurnal
with decreasing Tc. North American porcupines and rodents from the Hystricidae family are
known to be essentially nocturnal (Roze 1989, Roll et al. 2006). However, only 47% of
porcupines' active time was during the night and porcupines were more diurnal at cold
temperatures. Rodents living in cold environments are more 1ikely to be diurnal, possibly
because they exploit the walmer hours of the diel cycle (Roll et al. 2006). Still, diel activity
patterns are phylogenetically constrained (Roll et al. 2006). Hence, being cathemeral (i .e.
being active during both day and night, Tattersall 1987, Tattersall 2006) may represent the
best compromise nocturnal animais like porcupines can make to avoid exposure to cold night
temperatures. Porcupines also became more diurnal when snow penetrability increased and
one hypothesis is that being active during the daytime reduced the likelihood of encountering
predators (Bakker et al. 2005).
As we could expect from our thermal map, using a den was at the basis of porcupines'
behavioural thermoregulatory strategy. Porcupines modified the time spent outside of the den
and the timing of activity according to Tc, and this may allow huge energy savings (this
study, Humphries et al. 2005).
Microhabitats used outside of the den
Outside their dens, porcupines mainly used coniferous trees. Operative temperature did
not influence microhabitat use once porcupines were inside coniferous trees. Rather, the
microhabitat choice varied with the behaviour of the animal: porcupines preferentially
exploited open microhabitats and tops of trees for feeding and covered microhabitats and
bottoms of trees for resting. According to our thennal map, energy expenditure was generally
higher in open and arboreal than in other microhabitats. Feeding sites therefore did not appear
to be chosen based on the protection they offered against the thennal environment. We
generate the testable hypothesis that porcupines fed on tops of trees because they offered the