Initiation of breeding after winter in bank voles: effects of food and population density

Abstract

We studied factors causing variation in the initiation of reproduction after winter in the bank vole (Clethrionomys glareolus), an iteroparous seasonal breeder, by offering different winter food supplements and monitoring local density variation. We used either sunflower seeds or barley to supplement the diet of populations of bank voles in grassland enclosures. In a parallel experiment we used spruce seeds, a natural winter food, to supplement the diet of bank vole populations in unfenced spruce forest. Survival, maturation, and breeding were monitored by livetrapping. Population density decreased during winter in grassland enclosures and remained constant in the forest, with no difference between food treatments. Breeding was initiated earlier in the grassland enclosures than in the forest, probably because of the supplemental food supply in both seed treatments and social and environmental stability in enclosures. Within both experiments, we found no differences in timing of parturition between food treatments. Interactions of food treatment with density of females influenced the time of initiation of breeding in both experiments. At low densities, breeding started up to 1 month earlier than the population average. At high densities, a proportion of females did not breed during spring. Massive food supplements advanced the initiation of breeding, but among animals with similar food supplies, local population density seemed to have stronger regulatory effects. Local density variations may therefore create asynchronous breeding patterns within populations under similar wintering conditions. Résumé : Nous avons étudié les facteurs responsables de la variation dans le déclenchement de la reproduction après l'hiver chez le Campagnol roussâtre (Clethrionomys glareolus), un reproducteur saisonnier itéropare, par l'addition de différents suppléments alimentaires en hiver et par l'étude de la variation locale de la densité. Nous avons donné comme suppléments alimentaires des graines de tournesol ou de l'orge à des populations gardées en enceinte dans des zones herbeuses. Dans une expérience parallèle, nous avons fourni des graines d'épinettes, aliment utilisé en nature en hiver, à des populations de campagnols libres dans des forêts d'épinettes. La survie, la maturation et la reproduction ont été suivies par piégeage de campagnols vivants. La densité des populations a diminué en hiver dans les enceintes, mais elle n'a pas changé en forêt et il n'y avait pas de différence selon les traitements alimentaires. La reproduction était plus hâtive dans les enceintes en milieux herbeux qu'en forêt, probablement à cause des suppléments alimentaires des deux types de graines et à cause de la stabilité sociale et environnementale prévalant dans les enceintes. Nous n'avons pas constaté de différences dans le moment de la parturition selon le traitement alimentaire. Les interactions entre les traitements alimentaires et la densité des femelles influençaient le déclenchement de la reproduction. À densité faible, la reproduction pouva...

Is reproduction of the Australian house mouse (Mus domesticus) constrained by food? A large-scale field experiment

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Voles on small islands: effects of food limitation and alien predation

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