Ecological correlates of mortality of roe deer fawns in a predator-free environment

Abstract

The mortality of roe deer (Capreolus capreolus) fawns in summer was studied on Storfosna Island (10 km²), a predator-free island 2 km off the west-central coast of Norway, during a period of rapid population increase. Between 1991 and 1994 the population density increased from about 10 to 40 roe deer/km 2 . During this period 285 live and 36 stillborn fawns were found and the live fawns were all subsequently radio-collared. All observed mortality occurred within the first 35 days of life. The main causes of death were stillbirth, starvation/hypothermia, drowning, car accidents, and falls. The average annual total mortality for all 4 years was 18%. Although there was a large increase in mortality between 1991 and 1992 (from 10 to 18%), there was little subsequent increase in the last 3 years, resulting in an overall weak density dependence in total mortality. However, the proportion of stillbirths (5% in 1991 to 15% in 1994) showed a clear and significant trend toward an increase with increasing density. Low temperatures in April, which strongly affect the timing of the spring flush of high-quality forage during late gestation, also tended to contribute to higher mortality. Fawns that died were found to have reduced individual growth rates prior to death compared with fawns that survived. Fawns born to relatively light mothers or in triplet litters had higher mortality rates than those born to heavy mothers or in smaller litters. Maternal age and date of birth or sex of fawn had no effect on mortality.Résumé: La mortalité des faons en été a été étudiée chez le Chevreuil (Capreolus capreolus) dans l'île de Storfosna (10 km²), à 2 km au large de la côte centre-ouest de la Norvège, au cours d'une période d'augmentation rapide de la densité en l'absence de prédateurs. La densité de la population a augmenté d'environ 10 à 40 chevreuils/km² de 1991 à 1994. Au cours de cette période 285 faons vivants et 36 faons mort-nés ont été trouvés et les faons vivants ont par la suite été munis d'un collier émetteur. Tous les cas de mortalité observés se sont produits au cours des 35 premiers jours de la vie. Parmi les causes de mortalité, les principales étaient la mort à la naissance, l'inanition/hypothermie, la noyade, les accidents de la route et les chutes. Le taux annuel moyen de mortalité totale calculé sur les 4 ans a été de 18%. Il s'est produit une augmentation importante du taux de mortalité entre 1991 et 1992 (de 10 à 18%), mais ce taux a peu changé au cours des 3 années subséquentes, si bien que dans l'ensemble la mortalité totale au cours de toutes les années a été peu influencée par la densité. Cependant, la proportion de mort-nés (5% en 1991 à 15% en 1994) a démontré une tendance nette et significative à l'augmentation en fonction de la densité. Des températures basses en avril, qui enrayent fortement l'éclosion printanière du brout de haute qualité vers la fin de la gestation, avaient également tendance à augmenter la mortalité. Les faons qui sont morts avaient des taux individuels de croissance plus lents avant le...

Can Supplemental Feeding of Red Foxes Vulpes vulpes Increase Roe Deer Capreolus capreolus Recruitment in the Boreal Forest?

“…However, our estimated mortality rate of , 24% is not particularly high in comparison to studies of other species in predator-free environments but rather low for an area with predators (Andersen & Linnell 1998). Gill (1994) found a mean mortality rate of 26% for roe deer fawns, in a 23-year data set from England in a predator-free area, and in studies of other free-ranging ungulates in predatorfree environments, neonate mortality has been reported to range between 10 and 20% (red deer (Guinness et al 1978), white-tailed deer (Ozoga &Verme 1986, McGinnes & Downing 1977, moose (Stubsjoen et al 2000)).…”

Factors affecting maternal care in an income breeder, the European roe deer

“…However, variation in population density affected the family effects: in years of high population density the birth weights of fawns was low, and a high proportion of fawns died soon after birth. In the same study area Andersen & Linnell (1998) showed a strong relationship between density and the proportion of still‐born fawns. We suggest that income breeders like roe deer, which rely heavily on the availability of resources during the reproductive period, need to have mechanisms to adjust the level of maternal care: the selective absorption of a foetus could be such a mechanism.…”

“…Because offspring survival is unpredictable in income breeders (Gaillard, Festa‐Bianchet & Yoccoz 1998b), including roe deer (Gaillard et al . 1997, 1998a; Andersen & Linnell 1998), successful raising of offspring will depend mostly on resource availability during lactation, for which females have no information during gestation. Roe deer mothers should thus be selected to maximize the number of offspring to produce according to their body weight.…”

“…In laboratory rodents (Mendl 1988) offspring from large litters tend to be lighter at birth, have a slower growth rate and have a higher postnatal mortality. Earlier studies of the wild Storfosna population and a wild population in Chizé (Andersen & Linnell 1997, 1998; Gaillard et al . 1997) confirm that several of these traits are found in roe deer as well.…”

Individual access to preferred habitat affects fitness components in female roe deer Capreolus capreolus

“…The fawns were captured and collared as described in Andersen & Linnell (1998). Litter size was estimated at birth (LS BIRTH ), 5 days after birth (LS 5 DAYS ) and 35 days after birth (LS 35 DAYS ).…”