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

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most beneficial food. Leaf chemistry varies with light exposure in the tree canopy (Hirose et
a l. 1989, Close et al. 2005) and open habitats and tops of trees receive more light than other
habitats. By feeding there, porcupines may access needles with higher nitrogen or energy
content, and therefore make the best of a bad job to acquire profitable food ev en if this
implies trading off nutrition against thermoregulation (Torres-Contreras & Bozinovic 1997).
Alternatively, but not exclusively, porcupines may forage on tops of trees because it lowers
probability of detection by predators.
Time spenl f eeding
Feeding time generally increased with decreasing Tc, probably because energy
requirements increased with thennal stress (Systad & Bustnes 2001). A non exclusive
hypothesis would be that porcupines' foraging abilities were lower at extreme temperatures
(Bozinovic & Vasquez 1999) which increased the time spent sem'ching or handling food. As
discussed above, porcupines increased feeding time at low Tc by intensifying feeding rate
rather than by spending more time outside. We therefore believe that cold temperatures did
not limit foraging abilities of porcupines, contrary to what Bozinovic and Vasquez (1999)
showed for degus (Oelodon degus) exposed to hot temperatures.
Sex differenees
At cold temperatures (Tc-5°C (i .e. Tc :::::;
estimated Tic for porcupines in southern Québec). Why males started to increase time spent
outside before females was unclear. Males, having a higher body size, may be better
protected than females against cold temperatures (Scholander et al. 1950a, McNab 1970) and
may therefore have lower Tic than females. At Tc>-5°C, females stmted increasing time spent
outside but males still spent 49 to 84% more time outside compared to females. This
difference in time spent outside may create sex differences in predation risk. lndeed, if being
outside increases probabil ity of being detected and/or killed by a predator (Lima & Dili 1990,
Blumstein 1998), then males were exposed to higher predation risk than females. We found
that an increase in snow penetrability had a more negative effect on the time spent outside by
males than by females. As said before, predation risk appears to be linked to snow conditions