Linking winter habitat use, diet and reproduction in snowy owls using satellite tracking and stable isotope analyses

Coupling isotope values of feathers and satellite tracking of individuals have the potential to reveal multi-season linkages between wintering habitat, diet and carry-over effects on reproductive parameters in migrating birds. Snowy owls Bubo scandiacus have multiple wintering tactics as they can use both terrestrial and marine resources during the non-breeding season, but their nomadic behaviour complicates their study. We assessed if inter-individual variability in the diet inferred by feather isotopes could be explained by habitat use in winter as determined by satellite telemetry and examined possible carry-over effects on reproduction. Seventeen breeding female snowy owls were equipped with satellite transmitters and sampled for stable isotopes (δ¹³C and δ¹⁵N) in feathers. We found a positive relationship between the use of the coastal and marine environments in winter and the contribution of marine resources to the diet of snowy owls in the previous year based on feather analysis. The proportion of marine contribution to the winter diet was variable among individuals and showed a weak negative relationship to summer body mass but not with laying date or clutch size. Our integrated approach shows the usefulness of isotope analyses to infer habitat use and expand the temporal coverage of radio-tracking studies.

Isotope values of California vole (Microtus californicus) hair relate to historical drought and land use patterns in California, USA

Increased drought frequency and intensity and agricultural intensification have been key stressors to ecological systems over the past century. Biological proxies (e.g., pollen, tree rings) have been used to track this environmental change; however, linking these changes to the ecology of organisms remains challenging. Here, we link historical drought records to conditions of high water-stress in grassland habitats through the stable isotope analysis of California vole museum specimens (Microtus californicus). Using museum collections spanning 118-years (1891-2009), isotope values of dated hair tissues were associated with statewide drought metrics on the Palmer Drought Severity Index. We observed a positive correlation between δ¹⁵N and δ¹⁸O values and drought severity. The range in δ¹⁵N values (~ 18‰) is greater than what would be expected as a result of dietary shifts across the landscape (~ 3‰), and is likely attributed to the combined effects of physiological responses of M. californicus and isotopic shifts in plant resources with increased water-stress. Geospatial patterns in δ³⁴S values of hair tissues reflect higher baseline isotope values in coastal habitats. However, comparably high δ³⁴S values in the southern-most inland localities suggest sulfur fertilization of croplands and subsequent transfer to surrounding grassland habitats in ³⁴S enriched forms. A broad δ¹³C range (- 28.7 to - 14.3‰) further suggests the consumption of C₃ and C₄ plant-based dietary proteins. As shown here, stable isotope analysis of museum collections can provide a climate and land use record based on the physiological performance and ecology of a study species in a region affected intensely by anthropogenic activities.

Sexual dimorphism and condition dependence in the anal pad of the small Indian mongoose (Herpestes auropunctatus)

Secondary sexual traits tend to be sexually dimorphic, and theory predicts that such traits should also be condition-dependent in a sex-specific manner. We investigate these phenomena in a field study of the small Indian mongoose (Herpestes auropunctatus (Hodgson, 1836); formerly Herpestes javanicus (É. Geoffroy Saint-Hillaire, 1818)), in the first attempt at understanding secondary sexual traits and sexual selection in this species. Small Indian mongooses are solitary and nonterritorial, and they likely depend on chemical (scent) rather than visual or acoustic signals for communication. Additionally, they possess a fleshy projection around their anus, the anal pad, thought to aid in scent-marking. Our results revealed strong male-biased sexual dimorphism in mass, skull and body lengths, canine diameters, and anal pad area. After controlling for the influence of body length, males were 31% heavier and possessed anal pads that were 68% larger than females’. Additionally, anal pad size was positively related to body size in males but not in females and was condition-dependent in males but not in females. Taken together, our findings provide indirect evidence that the anal pad might have evolved, at least in part, via sexual selection.