Kyle A. Cutting

Previous success and current body condition determine breeding propensity in Lesser Scaup: evidence for the individual heterogeneity hypothesis

ABSTRACT The decision to breed influences an individuals current and future reproduction, and the proportion of individuals that breed is an important determinant of population dynamics. Age, experience, individual quality, and environmental conditions have all been demonstrated to influence breeding propensity. To elucidate which of these factors exerts the greatest influence on breeding propensity in a temperate waterfowl, we studied female Lesser Scaup (Aythya affinis) breeding in southwestern Montana. Females were captured during the breeding seasons of 2007–2009, and breeding status was determined on the basis of (1) presence of an egg in the oviduct or (2) blood plasma vitellogenin (VTG) levels. Presence on the study site in the previous year, a proxy for adult female success, was determined with stable isotope signatures of a primary feather collected at capture. Overall, 57% of females had evidence of breeding at the time of capture; this increased to 86% for females captured on or after peak nest initiation. Capture date and size-adjusted body condition positively influenced breeding propensity, with a declining body-condition threshold through the breeding season. We did not detect an influence of age on breeding propensity. Drought conditions negatively affected breeding propensity, reducing the proportion of breeding females to 0.85 (SE = 0.05) from 0.94 (SE = 0.03) during normal-water years. A female that was present in the previous breeding season was 5% more likely to breed than a female that was not present then. The positive correlation between age and experience makes it difficult to differentiate the roles of age, experience, and individual quality in reproductive success in vertebrates. Our results indicate that individual quality, as expressed by previous success and current body condition, may be among the most important determinants of breeding propensity in female Lesser Scaup, providing further support for the individual heterogeneity hypothesis.

The Effects of Timing of Grazing on Plant and Arthropod Communities in High-Elevation Grasslands

Livestock grazing can be used as a key management tool for maintaining healthy ecosystems. However, the effectiveness of using grazing to modify habitat for species of conservation concern depends on how the grazing regime is implemented. Timing of grazing is one grazing regime component that is less understood than grazing intensity and grazer identity, but is predicted to have important implications for plant and higher trophic level responses. We experimentally assessed how timing of cattle grazing affected plant and arthropod communities in high-elevation grasslands of southwest Montana to better evaluate its use as a tool for multi-trophic level management. We manipulated timing of grazing, with one grazing treatment beginning in mid-June and the other in mid-July, in two experiments conducted in different grassland habitat types (i.e., wet meadow and upland) in 2011 and 2012. In the upland grassland experiment, we found that both early and late grazing treatments reduced forb biomass, whereas graminoid biomass was only reduced with late grazing. Grazing earlier in the growing season versus later did not result in greater recovery of graminoid or forb biomass as expected. In addition, the density of the most ubiquitous grassland arthropod order (Hemiptera) was reduced by both grazing treatments in upland grasslands. A comparison of end-of-season plant responses to grazing in upland versus wet meadow grasslands revealed that grazing reduced graminoid biomass in the wet meadow and forb biomass in the upland, irrespective of timing of grazing. Both grazing treatments also reduced end-of-season total arthropod and Hemiptera densities and Hemiptera biomass in both grassland habitat types. Our results indicate that both early and late season herbivory affect many plant and arthropod characteristics in a similar manner, but grazing earlier may negatively impact species of conservation concern requiring forage earlier in the growing season.

Use of Stable Isotopes to Investigate Keratin Deposition in the Claw Tips of Ducks

Stable isotopes derived from the claws of birds could be used to determine the migratory origins of birds if the time periods represented in excised sections of claws were known. We investigated new keratin growth in the claws of adult female Lesser Scaup (Aythya affinis) by estimating the equilibration rates of stable isotopes (δ 13C, δ 15N, and δ 2H) from the breeding grounds into 1 mm claw tips. We sampled birds on their breeding ground through time and found that it took approximately 3–3.5 months for isotope values in most claw tips to equilibrate to isotope values that reflected those present in the environment on their breeding grounds. Results from this study suggest that isotopes equilibrate slowly into claw tips of Lesser Scaup, suggesting isotopes could potentially be used to determine the wintering grounds of birds. We suggest using controlled feeding experiments or longitudinal field investigations to understand claw growth and isotopic equilibration in claw tips. Such information would be valuable in ascertaining whether claw tips can be used in future studies to identify the migratory origins of birds.

Seasonal Change in Trophic Niche of Adfluvial Arctic Grayling (Thymallus arcticus) and Coexisting Fishes in a High-Elevation Lake System.

Introduction of non-native species is a leading threat to global aquatic biodiversity. Competition between native and non-native species is often influenced by changes in suitable habitat or food availability. We investigated diet breadth and degree of trophic niche overlap for a fish assemblage of native and non-native species inhabiting a shallow, high elevation lake system. This assemblage includes one of the last remaining post-glacial endemic populations of adfluvial Arctic grayling (Thymallus arcticus) in the contiguous United States. We examined gut contents and stable isotope values of fish taxa in fall and spring to assess both short- (days) and long-term (few months) changes in trophic niches. We incorporate these short-term (gut contents) data into a secondary isotope analysis using a Bayesian statistical framework to estimate long-term trophic niche. Our data suggest that in this system, Arctic grayling share both a short- and long-term common food base with non-native trout of cutthroat x rainbow hybrid species (Oncorhynchus clarkia bouvieri x Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis). In addition, trophic niche overlap among Arctic grayling, hybrid trout, and brook trout appeared to be stronger during spring than fall. In contrast, the native species of Arctic grayling, burbot (Lota lota), and suckers (Catostomus spp.) largely consumed different prey items. Our results suggest strong seasonal differences in trophic niche overlap among Arctic grayling and non-native trout, with a potential for greatest competition for food during spring. We suggest that conservation of endemic Arctic grayling in high-elevation lakes will require recognition of the potential for coexisting non-native taxa to impede well-intentioned recovery efforts.

Characteristics of shrub morphology on nest site selection of Greater Sage-Grouse (Centrocercus urophasianus) in high-elevation sagebrush habitat

ABSTRACT Selection of nest sites directly influences reproductive success for Greater Sage-Grouse (Centrocercus urophasianus); thus, regional evaluation of how this species selects nest sites is necessary for effective habitat management. We evaluated fine-scale nest site selection of Greater Sage-Grouse in the Centennial Valley of southwest Montana. We conducted vegetation surveys at nest sites (n = 90) of radio-tagged Greater Sage-Grouse and paired random locations across 2 breeding seasons (2014–2015). The majority of nests were located under mountain big sagebrush (Artemisia tridentata ssp. vaseyana), three-tip sagebrush (A. tripartita), and basin big sagebrush (A. tridentata ssp. tridentata) shrubs. We used generalized linear models and information theory to evaluate competing hypotheses about nest site selection. Our top model indicated that nest site selection was primarily associated with nest shrub morphological characteristics and cover provided by the nest shrub. Mountain big sagebrush and three-tip sagebrush provided twice the amount of lateral cover that basin big sagebrush shrubs provided. Our results suggest that herbaceous cover was unimportant at fine scale nest site selection of Greater Sage-Grouse in our study area. Managers should focus on conserving large intact stands of mountain big sagebrush and three-tip sagebrush habitats because they provided the most lateral cover and supported the majority of nest sites.