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

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precipitation, snowfall, and spring temperature over the past 130 years. As for the snowshoe
hares, one possible mechanism linking solar activity to porcupine abundance could be that
the solar activity affects snow conditions which may in turn affect access to food resources
(Roze 1989) or hunting behaviour of predators (e.g. coyotes, Thibault & Ouellet 2005). The
solar activity could also influence spring tempe rature which can have direct effects on
thermoregulation of juvenile porcupines (Haim et al. 1992) or indirect effects on condition of
individuals through an impact on vegetation growth (Albon et al. 1987, Langvatn et al. 1996,
Post & Stenseth 1999). Klvana et al. (2004) did not identify the mechanism(s) linking
porcupine abundance to weather conditions but their study, made on a large temporal and
spatial scale, raised the hypothesis that solar activity influenced population dynamics of
porcupines through an effect on local weather variables. Following the approach suggested
by Root and Schneider (1995), we set up a study on a smaller temporal and spatial scale, and
in the same porcupine population as in Klvana et al. (2004) to challenge this hypothesis and
shed light on the mechanism(s) lin king porcupine abundance to weather conditions.
We stm1ed a multi-annual capture-recapture study that allowed us to estimate annual
population size, "summer" (May to August), and "winter" (August to May) survival rates
separately, and to determine causes of mortality for the carcasses we found. Reliable
estimates of annual survival rates have been calculated using capture-recapture designs for
several mammal species (e.g. Jorgenson et al. 1997 on bighorn sheep, Bonenfant et al. 2002
on red deer, Ozgul et al. 2006 on yellow-bellied marmots, Baker & Thompson 2007 on monk
seals) but calculations of seasonal survival rates from individual-based capture-recapture data
are infrequent, especially in mammals (but see Lima et al. 2001 on mouse opossums, Crespin
et al. 2002 on bank voles, Lima et al. 2002a on leaf-eared mouse, Sendor & Simon 2003 on
pipistrelle bats). Using seasonal survival rates is crucial to understand how mortality risks
faced by animais vary during their annual cycle (Gauthier et al. 2001). ln pm1icular, in our
system, we were interested in distinguishing effects of spring temperature on summer and/or
winter survival and in assessing differences in variability between winter and summer
survival rates.
Our study, based on a small temporal and spatial scale, allowed us to test for a
relationship between porcupine abundance, solar activity, and local weather, and to determine
whether the effects of local weather on porcupine abundance are mediated tlu'ough changes in