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

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Ta, first because of the effects of wind and solar radiation on heat load (Lustick et al. 1978,
Bakken 1991), and second becallse microclimates can be highly heterogeneolls in space
(Chappe Il et al. 1978, Sharpe & Van Horne 1999). An accurate thennal map of an animal's
environment is therefore necessary to evalliate the ecological effectiveness of its
thennoreglilatory behaviollr. Comprehensive and detailed stlldies are needed to lInderstand
the complex interactions existing between thermal conditions and behaviour, especially in
cold environments.
The North American porcllpme (Erethizon dorsatum) is the only arboreal folivorous
mammal of the boreal forest. Porcupines stay active year round and rely on low quality food
(mainly bark and leaves of conifers) dllring winter. The lower critical temperatllre (Tic,
temperature below which an organism increases basal metabolic rate) of winter acclimatized
porcupines can vary between + 1 aoc and -12°C, depending on the size and origin of the study
animal (Irving et al. 1955, DeMatteo & Harlow 1997, Fournier & Thomas 1999). ln southern
Canada, Tic of porcupines lie around -2°C (Fournier & Thomas 1999) and individuals are
exposed, during winter, to temperatures that are well below Tic. Porcllpines can den to avoid
the coldest temperatures, but must exit the den daily to feed. Wind speed increases with
height above ground (Rosenberg 1974, Byman et al. 1988) so feeding in trees sholild be
energy demanding. However, the tree canopy is also highly heterogeneous in terms of
microhabitats available to a mid-sized mammal. How porcupines use their den and select
feeding microhabitats could greatly affect their thermoregulatory costs. We used one
population of free-ranging porcupines in southern Canada to investigate how thennal
conditions affected their habitat use and activity patterns during winter.
Our objectives were 1) to establish a detailed map of microclimates available to
porcupines, 2) to characterize activity patterns of porcupines according to the thermal
environment, 3) to evaluate whether microhabitat use of porcupines was detennined by
thermal constraints. What makes the cUITent report significant is that we modelled the
thermal environ ment at a very fine scale and compared the resulting thennal map with
detailed behavioural data from individually-marked, wild animais.