Pierre Delattre

Dietary response of Barn Owls (Tyto alba) to large variations in populations of common voles (Microtus arvalis) and European water voles (Arvicola terrestris)

The diet of the Barn Owl (Tyto alba (Scopoli, 1769)) was studied over an 8-year period in the Jura mountains of France, during two population surges of its main rodent prey (common voles (Microtus arvalis (Pallas, 1778)) and European water voles (Arvicola terrestris (L.,1758))), allowing us to test whether T. alba is an opportunistic predator as is often cited in the literature or exhibits more complex patterns of prey selection as is reported in arid environments. Small mammals were sampled by trapping and index methods. We observed (i) significant correlations between the proportions of A. terrestris and M. arvalis and woodland rodents in the diet and their respective densities in the field; (ii) interactions between populations of A. terrestris and M. arvalis, indicating that the proportion of each species in diet was affected by the density of the other; (iii) proportions of red-toothed shrews (genus Sorex (L., 1758)) in the diet did not correlate with their abundance in the field, indicating that those species were likely to be preyed upon when others were no longer available. This confirms that T. alba is generally opportunistic; however, prey selection of a focal species (e.g., Sorex spp., grassland species) can be affected by the density or availability of the other prey species

Is the prevalence of Taenia taeniaeformis in Microtus arvalis dependent on population density

Populations of common voles Microtus arvalis were studied as hosts of the tapeworm Taenia taeniaeformis during a 14-yr survey. They were monitored in spring, summer, and autumn in a pastoral ecosystem in eastern France. A total of 7,574 voles were sampled during 2 multiannual population fluctuations. A third fluctuation was sampled during the increase phase only. Overall prevalence was lowest in summer (0.6%), increased by 3 times in autumn (1.5%) and a further 5 times in spring (7.8%). Analysis of prevalence, based on 7,384 voles, by multiple logistic regression revealed that extrinsic factors such as season and intrinsic factors such as host age and host density have a combined effect. In the longer term, host age and host density were positively associated with prevalence in summer. Host density was strongly associated with autumn prevalence. There was no association between the fluctuation phase and prevalence. The study shows that a long timescale (here a multiannual survey) is necessary to demonstrate the positive effect of host density on the prevalence of this indirectly transmitted parasite. The demonstration of this relationship depends on the rodents being intermediate rather than definitive hosts.

Influence of edge effects on common vole population abundance in an agricultural landscape of eastern France

Vole demographics are often modified close to wooded environments. Population monitoring in such settings reveals substantial edge effects, although these have seldom been quantified. This study compares the abundance of common voleMicrotus arvalis (Pallas, 1778) populations at various distances from three types of wooded environment (hedgerow, copse and forest) and in two types of habitat (temporary and permanent grassland). In temporary grassland, substantial edge effects were detected along the boundaries of forests and hedgerows. At 100 m from the forest edge, voles were twice more abundant than at 50 m, four times more than at 25 m and eight times more than at 5 m. In permanent grassland, the edge effect was such that voles were practically absent up to 100 m from the forest edge. For both types of grassland, the edge effect was more pronounced for forest habitat than for hedgerows, that is, for elements with a large surface area of wooded environment. Our results suggest that landscape context may greatly affect the local abundance of voles. Given the considerable damage done byM. arvalis, the presence of wooded patches in grassland areas leads to lower vole densities in adjacent areas and this might be an alternative method to controlM. arvalis as a pest species.

Numerical response of a helminth community in the course of a multi-annual abundance cycle of the Water Vole ( Arvicola terrestris )

The impact of parasitism on population dynamics is determined in part by the numerical responses of parasites during population fluctuations of their hosts. Vole populations fluctuate in multi-annual cycles allowing such responses to be studied over successive phases of population growth, abundance and decline. We investigate how a helminth community (5 nematode and 7 cestode species) evolved over a full 6-year Water Vole (Arvicola terrestris) population cycle. Brillouin and individual parasite species richness (IPSR) indices were used to measure the numerical response of the parasite community. We report a correlation between levels of parasite intensity and vole population cycle phases. Both indices were consistently higher during pre-decline and decline phases for male and female voles alike. The numerical response of the parasite community suggests that populations may be regulated by parasitism and that studies of this mechanism should allow both for the cyclic or non-cyclic character of the host populations and for the response of the broadest possible set of the local parasite community.

Natural infection of the water vole Arvicola terrestris with Toxoplasma gondii, on the Jura plateau, eastern France.

102 A. terrestris (all juveniles) were caught between July 1992 and July 1993 from an area near the French village of Le Souillot, dissected and examined for coccidian tissue cysts. Five of the animals were found to have tissue cysts in their brains. Although histological sections of the 5 infected brains all revealed round cysts, each measuring <150 micro m in diameter, 2 of the brains had cysts that were morphologically similar to those of T. gondii, with crescent-shaped zoites. The cysts in the other three brains had spherical zoites, each with a central nucleus. Immunoperoxidase labelling confirmed the two brains had T. gondii cysts (2%). The cysts in the other 3 infected brains, which showed no reaction with the anti-Toxoplasma or anti-Neospora sera, were assumed to be young cysts of Frenkelia.

Feeding habits of the common genet (Genetta genetta) in the area of Djurdjura, north of Algeria

Abstract The purpose of our study was to characterize the diet of the common genet Genetta genetta in the Djurdjura Mts., north of Algeria. Through a year-round survey, we collected 360 feces and identified 1970 items. Arthropods (33%) and mammals (25%) were dominant, followed by wild birds and plants. The wood mouse Apodemus sylvaticus (65% within mammals) and Coleoptera (66% within arthropods) were dominant throughout the seasons. We observed striking seasonal variations in the common genet’s diet, with arthropods peaking in summer, mammals and wild birds dominating in winter, and energetic plants more consumed in autumn. Our study underlined the opportunistic feeding habits of the common genet with high values of trophic indices throughout the seasons, and the species’ capacity to adjust its food spectrum on seasonal resource availability. Our results confirmed that the common genet has an intermediate diet between generalist and specialist, feeding on a wide spectrum of items but relying on the wood mouse as the main energetic source. The diet of the species in Djurdjura Mts. included a great proportion of arthropods, thus, reflecting the “Mediterraneity” of the feeding spectrum of the common genet in northern Algeria.