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84 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
85 use of coyer influenced summer survival of juveniles. Juvenile porcupines weigh about 400g at bilth and are potentially exposed to both predation and hypothermia. Potential predators of juvenile porcupines inc\ude the great horned owl (Bubo virginianus), the lynx (Lynx canadensis), the bobcat (Lynx rufils), the coyote (Canis latrans), the wolf (Canis lupus), the wolverine (Gulo luscus), the mountain lion (Fe lis concolor) and the fisher (Martes pennanti) (Roze 1989). Fishers, coyotes, and great horned owls were ail regularly observed in our study area, therefore exposing juveniles to a significant predation risk. Yet, juvenile porcupines are born in mid-May when air tempe rature in our study site may still be as low as O°e. We thus expected juvenile porcupines to face a clear trade-off between using coyer to decrease predation risk and avoiding co ver to increase solar heat gain. ln such a situation, two scenarios can be proposed. First, if predation is the main factor limiting survival in our population we would expect juveniles to select for coyer, and juveniles using the more protective coyer to survive better. Second, if hypothermia is the main limiting factor, we would expect juveniles to select areas offering the best thennal environment (i .e. in the daytime, open areas), and juveniles using the more open areas to survive better. We expected predation to be the main factor limiting survival in our population because predation rates on porcupines of ail age classes were substantial during the study period, leading to a large decline in the size of our population (chap. 3). The main goal of our study was to determine whether juvenile porcupines selected for coyer (considered at two spatial scales) to avoid predators, and whether use of cover at one or the other scale enhanced survival. We tested the following predictions: 1) selection for cover occurs at both spatial scales because juvenile porcupines are highly vulnerable to predation (Sweitzer & Berger 1992). 2) juveniles are more likely to use open areas under cold conditions. Even though we predicted avoidance of predators to be the main factor driving habitat selection by juveniles, we expected risk of hypothermia to be high on cold days and therefore to influence habitat use on those days. Juvenile porcupines are poorly insulated (Haim et al. 1992) and may be faced with relatively low tempe ratures during their first weeks of life. We therefore expected them to trade off protection from predators with access to radiative heat gain by using open habitats wh en sun was shining (i.e. during the daytime) but air temperature was low.
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UNIVERSITÉ DU QUÉBEC À RIMOUSKI
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Remerciements Cette thèse n'aurait
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Table des matières LISTE DES TABLE
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Liste des tableaux Chapitre 3 Table
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VB Table 4.2 Power consumed (in Wat
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Liste des figures Chapitre 1 Figure
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XI Figure 2.3 Number oftimes ajuven
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Xlll Figure 4.3 Time spent outside
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Liste des annexes Annexe 1 Descript
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Chapitre 1 Introduction 1.1 Impact
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3 L ' importance relative des facte
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5 des populations ne donne qu' une
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7 (Tympanuchus pallidicinctus) les
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9 1940 1000 1960 139---------- c ~
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1 1 (Roze 1987). Ils perdent 10 à
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13 140 a) 1 20 - o -l- 2000 2001 20
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15 manipulations et la pose d'émet
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Chapitre 2 Handling North American
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19 information is lacking in the pu
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21 We searched for juvenile porcupi
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23 Switzerland). To check sex and r
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25 transmitters fo r larger units s
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27 8 a) 7 "0 c: :l 0 6 -If) ~ c: 5
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29 record sex, reproducti ve status
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Chapitre 3 Predation as a possible
Page 51 and 52: 33 3.2. Introduction A growing numb
Page 53 and 54: 35 predation risk. To do so, we tes
Page 55 and 56: 37 Table 3.1 : Monitoring effort ac
Page 57 and 58: 39 winter precipitation (total prec
Page 59 and 60: 41 emaciated), road kills, dead fro
Page 61 and 62: 43 Seasonal survival rates The sele
Page 63 and 64: 45 >. 1.0 0.9 ..... 0.8 .c ta .c 0.
Page 65 and 66: 47 Causes of mortality We assigned
Page 67 and 68: 49 100 - 90 a) 80 1/) c: .2 iii ...
Page 69 and 70: 51 too simplistic to detect complex
Page 71 and 72: 53 correlated with winter survival
Page 73 and 74: 55 4.1. A bstract Because the clima
Page 75 and 76: 57 Ta, first because of the effects
Page 77 and 78: 59 Third, we evaluated the behaviou
Page 79 and 80: 61 pattern of den use over one or t
Page 81 and 82: 63 two modali ties, Table 4.1, mode
Page 83 and 84: 65 feeding behaviour for the popula
Page 85 and 86: 67 of Tc we considered. However, we
Page 87 and 88: 69 Calculating TefrOIn Ta, wind spe
Page 89 and 90: 71 Number and duration of activity
Page 91 and 92: 73 8 o _ --L-_ 0 Operative temperat
Page 93 and 94: 75 Beschta 2004). Predation rates w
Page 95 and 96: 77 in our population (chap. 3). Mal
Page 97 and 98: 79 Tableau 4.5 : Pourcentage d'obse
Page 99 and 100: 81 associées avec le temps de surv
Page 101: 83 5.1. Abstract ln many mammals, j
Page 105 and 106: 87 juvenile was moving to escape fr
Page 107 and 108: 89 individual (using approximations
Page 109 and 110: 91 den use (treated as a binary var
Page 111 and 112: 1 93 20 - 18 ~ a) DAvailable .Used
Page 113 and 114: 95 80 -, 70 l DAvailable .Used 60 -
Page 115 and 116: 97 Table 5.3: Use of coyer by juven
Page 117 and 118: 99 juveniles. At the microhabitat s
Page 119 and 120: 101 However, we think protection fr
Page 121 and 122: 103 we found that most mortalities
Page 123 and 124: Chapitre 6 Conclusion Dans le cadre
Page 125 and 126: 107 porcs-épics fréquentent les c
Page 127 and 128: 109 épies, via un impact des condi
Page 129 and 130: II I Hiver E n hi ver, on montre qu
Page 131 and 132: 113 compromis auquel les animaux fo
Page 133 and 134: 11 5 En été, la mortalité des je
Page 135 and 136: 117 pékan dans la région. On mont
Page 137 and 138: 119 Annexe 2 Étalonnage des modèl
Page 139 and 140: 121 Références Aanes, R. , & R. A
Page 141 and 142: Bult, A., & C. B. Lynch. 1997. Nest
Page 143 and 144: 125 Creel, S. , 1. Winnie, B . Maxw
Page 145 and 146: 127 Fortin, D., & G. Gauthier. 2000
Page 147 and 148: 129 Hik, D. S. 1995. Does risk of p
Page 149 and 150: Lent, P. C. 1974. Mother-infant rel
Page 151 and 152: 133 Murray, D. L. , & S. Boutin. 19
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au Québec depuis 1984. Ministère
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137 Proceedings of the Royal Societ
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139 Tsiropoula, G. 2003. Signatures
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