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

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intensity, potentially to avoid wetting their coat with raindrops left on vegetation by the rain.
The fact that juveniles didn't modify the use of coyer outside of the den with changing
temperature conditions suggests that coyer outside of the den was rather used as a hiding
co ver, with juveniles retreating to dens wh en temperature decreased.
Habitat use and survival
Predation was the main cause of mortality in juvenile porcupines. Several predators hunt
and kill porcupines more effectively in open habitats (coyotes: Keller 1935, mountain lions:
Robinette et al. 1959, fishers: Powell & Brander 1977) and porcupines perceive open habitats
as risky habitats (Sweitzer & Berger 1992). Consistent with the hypothesis that open habitats
are more risky, we found that use of coyer (both at the microhabitat and local scales)
enhanced survival. There were individual differences in the use of coyer and juveniles
survived better when using habitat patches with high shrub coyer and, within those patch es,
when using microhabitats with high protective coyer. Numerous studies have reported that
ungulate fawns bed down in dense ground coyer (review in Mysterud & Ostbye 1999) but
only a few studies have related habitat use to survival (Linnell et al. 1995, Aanes & Andersen
1996, Canon & Bryant 1997, Farrner et al. 2006). ln addition, studies on rodents (Moreno et
al. 1996, Schooley et al. 1996, Ebensperger & Hurtado 2005) suggested that coyer may be
obstructive rather than protective for small mammals. Here we exploited a multivariate and
hierarchical analysis of habitat use by juvenile porcupines to show that use of coyer at both
scales studied enhanced survival of one small-bodied animal. Use of coyer indeed has diverse
ecological consequences depending probably partly on the size of the study animal, and on
the limiting factors with which it is faced (Mysterud & Ostbye 1999).
Besides individual differences in the use of coyer, we also found individual differences in
the use of dens, ground and trees. Juveniles survived better when using trees than when using
ground. We suggest that juveniles were more vulnerable to predators when they were on the
ground th an when they were in trees. Use oftrees prevents attack by sorne predators (e.g.
coyotes) but not from others (e.g. fishers, Powell & Brander 1977). According to the few
signs of presence we found, fishers appeared to be the main predators of juvenile porcupines
during the study period (results not shown) and the use of trees is therefore not expected to
decrease risk of attack. However, use of trees may have decreased detectability by fishers,
therefore leading to higher survival of juveniles. Our third prediction was suppOlted because