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

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juveniles. At the microhabitat scale, the type ofhiding site (den, ground, or tree) and the
amount of protective coyer significantly influenced sUl·vival (Table 5.5). For a given location,
use of si tes with high protective coyer enhanced survival (a 10% increase in the mean
protective coyer used was associated with a 66% decrease in death probability, Table 5.5).
Also, when taking into account the protective coyer used, use of trees enhanced survival
compared to use of ground locations (8% decrease in death probability, Table 5.5).
At the local scale, use of sites with higher shmb coyer significantly increased survival
(Table 5.5) when percentages oftree and herb coyer were taken into account. According to
the hazard ratio, a 10% increase in mean shrub coyer used was associated with a 74%
decrease in death probability. Also, when taking tree and shrub coyer into account, use of
sites with higher herb coyer decreased survival (78% increase in death probability, Table 5.5)
although this effect was not statistically significant. Finally we found no effect ofsex (X 2 1 =
0.30, P = 0.586), mass on 10 June (li = 0.01, P = 0.915), mobility (X21 = 1.94, P = 0.163), or
distance to the mother (li = 0.32, P = 0.570) on survival.
Table 5.5 : Coefficients for the survival analyses for 14 juvenile North American porcupines
studied in Parc National du Bic, Québec, May to August, 2003-2004
Variable ê value SE
j
"t,.-
P
Hazard ratio
M icrohabitat scale
Protecti ve coyer - 1.072 0.478 5.03 0.025 0.34 ( 10%)
Location
Ground 0 ND ND ND reference category
Den -0.026 0.030 0.75 0.388 0.97
Tree -0.089 0.037 5.89 0.015 0.92
Local scale
Tree coyer -0.2 13 0.272 0.61 0.433 0.81 (10%)
Shrub coyer -1.338 0.534 6.29 0.012 0.26 (10% )
Herb coyer 0.579 0.312 3.44 0.064 1.78 (10%)
5.5. Discussion
Juvenile porcupines showed selection for high protective coyer at the microhabitat (1m)
scale only. At the local (15 m) scale, juveniles selected sites characterized by a low herb
coyer and with cedar as dominant tree species. The use of coyer decreased as juveniles grew