Régime et cycles alimentaires de la Vipère d'Orsini (Vipera Ursinii Bonaparte, 1835) au Mont Ventoux, France

Résumé En Fr

The diet of Vipera ursinii was studied on the Mont Ventoux (Vaucluse, France) by examination of the contents of the stomach and/or the intestine obtained by massage. This species feeds principally on Orthoptera which represent 99 % of the number of prey identified, and over 98 % of the biomass ingested. These insects are very abundant in the habitat studied : in August there are 4 kg/ha, locally even more. The remainder of the diet is made up of small lizards (Podarcis muralis) and spiders (Philaeus chrysops). Small mammals are abundant on the sites studied ; they are readily eaten in captivity, but curiously, not by free-living vipers. The smallest Orthoptera eaten are 16-17 mm in total length, regardless of the size of the snake. Above this minimum size, all Orthoptera are eaten, apparently unselectively. Among species only one is generally not eaten, and this is the smallest, which only rarely exceeds 16 mm in length. The very largest Orthoptera are eaten by only the largest vipers. Such opportunities are rare, and the mean length of the prey eaten by the smallest vipers (Total Length � 30 cm) is not significantly different from the value for the largest individuals (T.L. � 40 cm). The ranges of prey-sizes consumed by the small and large vipers overlap considerably. Adult males emerge from their winter quarters around mid-April, as soon as the snow melts ; the females come out in the first half of May. It is surprising that potential prey which are available, and which are eaten in other circumstances such as small lizards and small mammals, are not consumed on the Mont Ventoux in May/June as they are in other populations of this species. The vipers of both sexes, whatever their size, do not feed until the second half of June when the largest Orthoptera reach the minimal size required by the vipers. The last meals are made at the end of September. The very short period of feeding is therefore three and a half months for all categories of the population. The immatures become active very late in the year, which is exceptional among vipers. They emerge at the time when feeding begins, in the second half of June, more than two months after the first adult males, and six weeks after the first females. Meals are frequent : the vipers feed on average every 2-4 days according to their age and reproductive status. The stomach contents are small, and represent only 3 to 7.2 % of the live weight of the vipers, according to their age and reproductive status. Breeding females continue feeding during the last two thirds of gestation ; during the moults, feeding continues, but at a slower rate.

Au Mont Ventoux, le régime de la Vipère d’Orsini est, pour plus de 99 % constitué d’Orthoptères, insectes très abondants dans le milieu, tandis que les Vertébrés tétrapodes, également présents ne sont pratiquement pas consommés. La sélection des proies ne dépend que de leur taille : les Orthoptères ne sont consommés qu’à partir de 16-17 mm de longueur totale. Cette taille minimale est la même quel que soit l’âge des vipères. La période d’alimentation, très courte, s’étend de la fin-juin à la fin-septembre pour toutes les vipères, quel que soit leur âge ou leur état sexuel. Les immatures n’entrent en activité qu’au début de la période d’alimentation : leur période annuelle d’activité s’étend sur environ 3,5 mois, contre environ 5 et 6 mois respectivement chez les femelles et les mâles adultes. Les prises alimentaires sont fréquentes et les contenus stomacaux petits. Les femelles gestantes se nourrissent pendant la gestation.