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

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survival of large herbivores constitutes an important issue in evolutionary ecology,
population management, and conservation (Linnell et al. 1995, Gaillard et al. 1998, Gaillard
et al. 2000 for reviews). One reason why juvenile survival is highly variable may have to do
with predation. Juveniles are highly vulnerable to predation because of their small size, low
mobility, and lack of experience (Molinari-Jobin et al. 2004, Hoogland et al. 2006). Newborn
mammals are often categorised as followers or hiders depending on their anti-predatory
strategy (Lent 1974). In species where juveniles follow their mother, mothers minimize
predation risk to their offspring by using habitats with fewer predators or greater
opportunities to evade predation (Bleich et al. 1997, Rachlow & Bowyer 1998). For species
relying on a hiding behaviour, characteristics of the hiding site may be important in
determining protection from predators. For example, it is weil documented that ungulate
fawns select hiding sites providing large amounts of cover (see review in Mysterud & Ostbye
1999), and presence of cover is believed to lower the risk of predation, either through
reduction of the detection probability, or through obstruction from attacks. However, even if
it is generally assumed that such habitat selection has important sUl"vival consequences,
studies relating use of cover to survival of juveniles are rare (but see Linnell et al. 1995 ,
Aanes & Andersen 1996, Canon & Bryant 1997, Fanner et al. 2006).
On the other hand, presence of cover decreases exposure to solar radiation (Demarchi &
Bunnell 1993) and some large mammals have been shown to use cover during summer to
reduce heat stress (Demarchi & Bunnell 1995, Dussault et al. 2004). For neonates that are
sensitive to hypothennia (Doolan & Macdonald 1997, Andersen & Linnell 1998, Gilbert &
Raedeke 2004, Oison et al. 2005), use of cover during sunny summer days may be
detrimental because it may decrease access to radiative heat gain (Bowyer et al. 1998). ln
particular, risk ofhypothennia increases with decreasing body size because animais with a
small body size have a high surface area to volume ratio, which means that they have a high
rate of heat loss to the environment (Scholander et al. 1950b, Kreith & Black 1980).
Although ungulate hiding fawns select for cover, with possible positive effects on survival, it
is therefore unclear whether selection for cover should be beneficial to hiding neonates of
smaller body size, that are relatively more susceptible to hypothennia.
ln this study, we used North American porcupines (Erethizon dorsatum), a medium-sized
mammal that relies on a hiding anti-predatory strategy (Roze 1989), to investigate how the