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

39
winter precipitation (total precipitation in mm, between November and April), snowfall (in
cm, between November and April) and spring temperature (mean monthly temperature in oC,
averaged over May and June). We obtained weather records from the Environment Canada
weather station at Rimouski, about 20 km from our study site (48°27'N, 68°31 'W). We
examined relationships between solar irradiance and weather parameters for years 1998 to
2004 because we tested for effects of environmental covariates on survival with lags of up to
two years (i.e. stalting in 1998) and because 2004 was the last population year we used in
survival analyses (see below). We standardized weather data before analyses.
Seasona! survival rates
We detennined fates of porcupines through capture, visual and radio-telemetry
observations (hereafter called porcupine observations). Survival analyses included only
porcupines that died naturally (i .e. not from research related reasons, see below). Our dataset
consisted in 82 females (12 captured for the first time as juveniles, 16 as subadults, and 54 as
adults) and 77 males (16 captured for the first time as juveniles, seven as subadults, and 54 as
adults). Preliminary analyses indicated that survival was similar for subadults and adults so
that we only considered two age classes: juveniles and individuals 2: l-yr-old. We used
methods detailed in Loison et al. (1994) to include different ages at capture in the estimation
procedures. We estimated seasonal survival rates of porcupines from May 2000 to May 2005
(k = Il occasions of captures). We defined as "summer survival" the survival from May-June
to August and as "winter survival" the survival from August to May-June. The lengths of our
"summer" and "winter" periods were thus four and eight months, respectively. We used
observations from May and June to determine presence at the beginning of summer because
using only May would have reduced our sample size (n = 139 instead of 159), especially for
juveniles (n = 18 instead of 28). lndeed, juveniles are born at the end of Mayor beginning of
June so that many of them were observed for the first time in June and died during their first
summer (i.e. were not observed in August).
We performed survival analyses using capture-mark-recapture methods (Lebreton et al.
1992), using the program M-SURGE 1.7.1 (Choquet et al. 2004, 2005) which can take into
account unequal interval lengths between capture occasions. The fit of our data to the
Cormack-Jolly-Seber model was acceptable (Goodness of fit test using U-CARE 2.02
(Choquet et al. 2003, Pradel et al. 2003): Chi 2 = 39.620, df= 29, P = 0.090) so that we used