Increased diet breadth of little brown bats (Myotis lucifugus) at their northern range limit: a multi-method approachThe distribution of small mammals is constrained by extreme environmental 24 demands and variable food supplies that are commonly incurred at northern latitudes. 25Little brown bats (Myotis lucifugus, Le Conte, 1831) are at the northwestern limits of 26 their range in Alaska, where environmental demands are higher and prey availability is 27 more seasonal than elsewhere in their range. We hypothesized that the little brown bat in 28 interior Alaska has adjusted to these constraints by broadening its foraging niche, relative 29 to that of southern conspecifics. We analyzed arthropod fragments (microhistology) in 30 guano to describe prey composition to Order. We compared the efficacy of evaluating 31 diet by microhistology with DNA analysis and stable isotope analysis on guano and hair. 32

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Contamination from detergent residues prohibited the use of detergent extraction in isolating forage (15)N from endogenous (15)N in the feces of herbivores. Although δ(15)N values in fecal fibers can be used to track dietary δ(15)N values in wild herbivores, discrimination between fecal extracts and diet may vary with the contribution of endogenous nitrogen (N), and, therefore, residual endogenous (15)N in feces may limit dietary reconstructions from fecal δ(15)N values for some large herbivores.

Abstract. Arctic caribou (Rangifer tarandus) have the longest terrestrial migration of any ungulate but little is known about the spatial and seasonal variation of minerals in summer forages and the potential impacts of mineral nutrition on the foraging behavior and nutritional condition of arctic caribou. We investigated the phenology, availability, and mechanistic relationships of calcium, phosphorus, magnesium, sodium, potassium, iron, manganese, copper, and zinc in three species of woody browse, three species of graminoids, and one forb preferred by caribou over two transects bisecting the ranges of the Central Arctic (CAH) and Western Arctic (WAH) caribou herds in Alaska. Transects traversed three ecoregions (Coastal Plain, Arctic Foothills and Brooks Range) along known migration paths in the summer ranges of both herds. Concentrations of mineral in forages were compared to estimated dietary requirements of lactating female caribou. Spatial distribution of the abundance of minerals in caribou forage was associated with interactions of soil pH and mineral content, while temporal variation was related to plant maturity, and thus nitrogen and fiber content of forages. Concentrations of sodium were below caribou requirements in all forage species for most of the summer and adequate only on the Coastal Plain during the second half of summer. Phosphorus declined in plants from emergence to senescence and was below requirements in all forages by mid-summer, while concentrations of copper declined to marginal concentrations at plant senescence. Interactions of sodium with potassium, calcium with phosphorus, and copper with zinc in forages likely exacerbate the constraints of low concentrations sodium, phosphorus, and copper. Forages on the WAH contained significantly more phosphorus and copper than forages collected on the CAH transect. We suspect that migrations of caribou to the Arctic Coastal Plain may allow parturient females to replenish sodium stores depleted by foraging inland through the long arctic winters, while also extending the availability of adequate phosphorus, if animals are able to selectively track emerging waves of forage.