The in¯uence of density on post-weaning growth in roe deer Capreolus capreolus fawns A. J. M. Hewison 1 *, J. M.Gaillard 2 , J. M. Angibault 1 , G.Van Laere 3 and J. P. Vincent 1 1 Institut de Recherche sur les Grands Mammife Áres, Institut National de la Recherche Agronomique, BP 27, Castanet-Tolosan Cedex, F 31326 France 2 Laboratoire de Biome Âtrie et Biologie Evolutive, Unite  Mixte de Recherche 5558, Universite  Claude Bernard Lyon 1, 43 boulevard du 11 novembre 1918, Villeurbanne Cedex, F 69622 France 3 Of®ce National de la Chasse, CNERA Cervide Âs-Sangliers, 85bis Avenue de Wagram, Paris Cedex, F75017 France (Accepted 17 July 2001) Abstract In temperate ungulates, the body weight of juveniles at the onset of winter is a crucial determinant of survival and can also in¯uence subsequent reproductive success. However, growth may be retarded post- weaning, during winter, as a result of resource restriction and/or the demands of thermoregulation in harsh climatic conditions. Post-weaning growth rates of juveniles were compared in relation to varying density in two populations of roe deer Capreolus capreolus (Chize Â, Dourdan) monitored for 10 and 15 years, respectively. Body growth of fawns continued over the post-weaning stage of the juvenile period (October± March) at the rate of 0.017 kg/day at Chize  and 0.014 kg/day at Dourdan. Deer density had no in¯uence on this post-weaning growth rate of juveniles in their ®rst winter. However, deer born in years of high density weighed less at a given date than those born in years of low density because of their smaller body size at the onset of winter, indicating density-dependent rates of growth before weaning. At Chize Â, the sexes grew at the same rate, but sexual dimorphism was apparent as males weighed about 1 kg (8%) more than females at a given date. At Dourdan, no signi®cant sexual dimorphism was detected, although females tended to be heavier than males at a given date. We conclude that density in¯uences juvenile body weight (through its effect on birth weight and/or post-natal growth rate) before weaning in this species and, despite continued growth after weaning, during winter, roe deer whose early growth is limited through interspeci®c competition cannot compensate for this early restriction. Key words: body size, cohort effects, compensation, density-dependence, sexual dimorphism, Capreolus capreolus INTRODUCTION Body weight is a critical factor in determining the survival and reproductive output of large mammals (Clutton-Brock, 1991). A certain proportion of varia- bility in adult body size originates from the effects of growth and development during the juvenile stage (e.g. bighorn sheep, Festa-Bianchet et al., 1996; fallow deer, Birgersson & Ekvall, 1997; roe deer, Gaillard, Boutin et al., 1997) with direct effects on juvenile survival (White et al., 1987; Clutton-Brock, Price et al., 1992), but also subsequent effects for life-history traits later in life (cohort effects sensu Albon, Clutton-Brock & Guinness, 1987). Individuals belonging to the same cohort (born during the same year) tend to have similar attributes (e.g. body weight) due to the fact that they experience similar conditions during the early life stages (see Lind- stro Èm, 1999 for a review; see Rhind et al., 1998; Pettorelli et al., 2001 for case studies). Cohort effects may be mediated by variation in levels of maternal investment during gestation and the early stages of life (generally in the spring and summer for large mammals) (e.g. Clarke, Yakubu & Symonds, 1997) or yearly varia- tion in post-weaning conditions of resource availability or climatic factors (generally the autumn and winter) (e.g. see Verme & Ozoga, 1980; Cook et al., 1996). Hence, it is important to determine at what life stage density-dependent resource restriction and other envir- onmental factors in¯uence juvenile growth (see Lindstro È m, 1999). Juvenile growth of northern or temperate species of deer is generally restricted or ceases altogether during the winter period (red deer, Mitchell, McCowan & J. Zool., Lond. (2002) 257, 303±309 # 2002 The Zoological Society of London Printed in the United Kingdom DOI:10.1017/S0952836902000900 *All correspondence to: A. J. M. Hewison. E-mail: hewison@toulouse.inra.fr