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

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5.1. Abstract
ln many mammals, juveniles are highly vulnerable to predators because of their low
mobility and small body size. Use of dense ground co ver by juveniles has been assumed to
lower predati on risk. On the other hand, use of coyer during sunny summer days decreases
access to radiative heat gain and may be detrimental fo r juveniles that are sensitive to
hypoth ennia. Studies relating use of coyer to survival of juveniles remain infrequent and
have been essentiall y performed on ungul ates. We measured habitat selecti on and monitored
surv ival of 14 North American juvenile porcupines. We tested 1) whether juveniles selected
for coyer at the microhabitat scale (within 1 m of the animal) and at the local scale (within 15
m), 2) whether use of coyer depended on meteorological conditions, and 3) whether use of
coyer influenced survival. We also examined how sex, body mass, mobility of the juvenile,
and di stance between juvenile and mother affected surviva l. Our results indicate th at j uvenile
porcupines selected microhabitats providing high protective coyer (microhabitat scale) within
areas showing low herb co ver (l ocal scale). Use of coyer depended on weather, with juveniles
using dens to avoid low air temperature and rain. Ten out of 14 juveniles di ed before the end
of the summer and nine out of 10 deaths were due to predati on. Habitat use (at both the
microhabitat and local scales) influenced survival. At the microhabitat scale, use of protective
coyer and use of trees enhanced survival compared to use of ground locations. At the local
scale, use of sites with high shrub coyer enhanced survival. We fo und no effect of sex, body
mass, mobility, and di stance to the mother on surviva l. These results supp0l1 the hypothesis
that predation was the main fa ctor limiting survival of juveniles in our populati on and that
predati on ri sk was modulated by habitat use of juveniles.
Key-words : climate, conditionallogistic regression, Erethizon dorsatum, hider-fo llower
behaviour, Québec, survival analysis
5.2. Introduction
ln large herbivores, juvenile survival is more sensitive to environmental variati on than is
adult survival (Gaill ard et al. 2000, Eberhardt 2002, Gaillard & Yoccoz 2003), and has been
reported to play a fundamental role in driving the dynami cs of several populations (Coul son
et al. 1997, Gaillard et al. 2000). Therefore, identifying the causes of vari ati on in earl y