Body Mass of Roe Deer Fawns during Winter in 2 Contrasting Populations

Abstract

Because first-year survival and age at sexual maturity of northern ungulates often depend on body mass of fawns during winter, knowledge of factors affecting body mass of fawns is necessary to understand population dynamics and management of ungulates in temperate regions. Therefore, we compared body mass of roe deer (Capreolus capreolus) fawns during winter in two enclosed populations with contrasting climatic and demographic characteristics: Chize (CH) in western France (mild winters, less abundant food and lower birthrates), and Trois Fontaines (TF) in eastern France (cold winters, abundant food and high birthrates). We weighed 2,077 fawns (1,212 in TF and 865 in CH) of both sexes captured with drive-nets in January and February from 1976 to 1993. Mass of male fawns was greater than of females in both populations (P < 0.01). Body mass varied among years for both sexes in each population (P < 0.01 in CH; P < 0.01 in TF). Neither climatic conditions between April and December nor population density accounted for yearly variation in body mass of fawns in TF. Rather, body mass fluctuated randomly about a mean, with no longterm effects on population dynamics. By contrast, body mass of fawns in CH was correlated with mean daily temperature in June-July (P = 0.01 for males; P = 0.04 for females) and population density (P = 0.02 for males; P = 0.03 for females). Body mass of fawns was greater in years following cool summers and in years of low population density (r 2 = 0.75, P < 0.01 for males; r 2 = 0.50, P = 0.02 for females). Mass of male fawns but not female fawns was greater in January-February when total rainfall in the previous April-May was low (P = 0.01). In CH, yearly variation in fawn body mass supports the range quality hypothesis which states that fawns entering winter are small owing to poor nutritional conditions the previous summer or high population density. As a consequence, yearly variations in body mass probably have long-lasting effects on population dynamics in CH.