We examined the stable isotopes of nitrogen and carbon in a small mammal, the red-backed vole (Clethroinomys gapperi (Vigors, 1830)), to determine if isotope signatures reflect diet composition. Nitrogen- and carbon-isotope ratios in tissues from voles maintained on different protein levels in the laboratory were compared with wild-trapped voles. The isotopic fractionation of dietary nitrogen and carbon was also examined as food was digested in the stomach, incorporated into bone collagen, bioapatite, and hair, and excreted as feces. Nitrogen and carbon isotopes were fractionated differently depending on the isotopic composition and protein content of the diet. δ15N and δ13C values appear to be influenced by factors in addition to diet, such as macronutrients metabolized for respiration, metabolic rate, and periods of protein shortage.

Small mammals are income breeders, but the degree to which females draw from maternal reserves and partition nutrients to the mammary glands in the wild is not known. This study examined stable-nitrogen and stablecarbon isotopes in red-backed vole, Clethrionomys gapperi (Vigors, 1830), hair to determine mother-offspring trophic relationships and to consider the extent to which voles rely on maternal reserves during lactation. Both dependent and independent young showed isotopic enrichment in 15 N and depletion of 13 C in their hair relative to mothers. We suggest that growing offspring, both dependent and independent, may catabolize body reserves to support both growth and moult. We propose that the nitrogen-and carbon-isotope compositions of hair may be more useful indicators of metabolic rate than mother-offspring trophic relationships in small mammals. Résumé :Les petits mammifères utilisent leurs apports énergétiques quotidiens (revenu) pour se reproduire; on connaît cependant mal dans quelle mesure les femelles en nature puisent dans leurs réserves maternelles et allouent des nutriments aux glandes mammaires. Notre étude examine les isotopes stables d'azote et de carbone dans le poil des campagnols à dos roux de Gapper, Clethrionomys gapperi (Vigors, 1830), afin de déterminer les relations trophiques mère-petits et évaluer dans quelle mesure les campagnols utilisent leurs réserves maternelles durant l'allaitement. Tant chez les petits dépendants qu'indépendants, il y a un enrichissement isotopique en 15 N et un appauvrissement en 13 C dans le poil, par comparaison à leur mère. Nous croyons que les rejetons en croissance, tant dépendants qu'indépendants, peuvent cataboliser leurs réserves corporelles pour alimenter la croissance et la mue. Nous croyons que la composition isotopique d'azote et de carbone du poil chez les petits mammifères est un indicateur plus fiable du taux métabolique que de la relation trophique mère-petits.[Traduit par la Rédaction] Sare et al. I 716

2005. Moulting patterns in Clethrionomys gapperi. Acta Theriologica 50: 561-569.Small northern mammals undergo regular developmental and seasonal moults. However, the moulting patterns of many small mammals are not well known. Development and subsequent moulting of the pelage was documented in adult red-backed voles Clethrionomys gapperi Vigors, 1830 and their offspring in relation to age, weight, and sex. Red-backed voles exhibited 4 developmental pelages (nestling, juveniles, subadult, and adult) through diffuse, rapid hair growth. Rapid growth was associated with early moulting at the nestling, juveniles and adult stages. However, a trade-off between moulting and growth existed at the subadult stage such that delayed moulting was associated with rapid growth. Adult voles completed a unique moult progression with highly variable timing. Male and female C. gapperi showed no differences in pattern or locations of moulting. Variation in the number and timing of moults in small mammals may reflect differences in life-history strategies and highlights the need for a consistent mammalian pelages and moults nomenclature.