Bruce W. Baker

INTERACTION OF BEAVER AND ELK HERBIVORY REDUCES STANDING CROP OF WILLOW

Populations of beaver and willow have not thrived in riparian environments that are heavily browsed by livestock or ungulates, such as elk. The interaction of beaver and elk herbivory may be an important mechanism underlying beaver and willow declines in this competitive environment. We conducted a field experiment that compared the standing crop of willow three years after simulated beaver cutting on paired plants with and without intense elk browsing (∼85% utilization rate). Simulated beaver cutting with intense elk browsing produced willow that was small (biomass and diameter) and short, with far fewer, but longer, shoots and a higher percentage of dead biomass. In contrast, simulated beaver cutting without elk browsing produced willow that was large, tall, and leafy, with many more, but shorter, shoots (highly branched) and a lower percentage of dead biomass. Total stem biomass after three years was 10 times greater on unbrowsed plants than on browsed plants. Unbrowsed plants recovered 84% of their pr...

GENETIC METHODS IMPROVE ACCURACY OF GENDER DETERMINATION IN BEAVERS

Abstract Gender identification of sexually monomorphic mammals can be difficult. We used analysis of zinc-finger protein (Zfx and Zfy) DNA regions to determine gender of 96 beavers (Castor canadensis) from 3 areas and used these results to verify gender determined in the field. Gender was correctly determined for 86 (89.6%) beavers. Incorrect assignments were not attributed to errors in any one age or sex class. Although methods that can be used in the field (such as morphological methods) can provide reasonably accurate gender assignments in beavers, the genetic method might be preferred in certain situations.

Associations of Grassland Bird Communities with Black‐Tailed Prairie Dogs in the North American Great Plains

Colonial burrowing herbivores can modify vegetation structure, create belowground refugia, and generate landscape heterogeneity, thereby affecting the distribution and abundance of associated species. Black-tailed prairie dogs (Cynomys ludovicianus) are such a species, and they may strongly affect the abundance and composition of grassland bird communities. We examined how prairie dog colonies in the North American Great Plains affect bird species and community composition. Areas occupied by prairie dogs, characterized by low percent cover of grass, high percent cover of bare soil, and low vegetation height and density, supported a breeding bird community that differed substantially from surrounding areas that lacked prairie dogs. Bird communities on colony sites had significantly greater densities of large-bodied carnivores (Burrowing Owls [Athene cunicularia], Mountain Plovers, [Charadrius montanus], and Killdeer [Charadrius vociferus]) and omnivores consisting of Horned Larks (Eremophila alpestris) and McCowns Longspurs (Rhynchophanes mccownii) than bird communities off colony sites. Bird communities off colony sites were dominated by small-bodied insectivorous sparrows (Ammodramus spp.) and omnivorous Lark Buntings (Calamospiza melanocorys), Vesper Sparrows (Pooecetes gramineus), and Lark Sparrows (Chondestes grammacus). Densities of 3 species of conservation concern and 1 game species were significantly higher on colony sites than off colony sites, and the strength of prairie dog effects was consistent across the northern Great Plains. Vegetation modification by prairie dogs sustains a diverse suite of bird species in these grasslands. Collectively, our findings and those from previous studies show that areas in the North American Great Plains with prairie dog colonies support higher densities of at least 9 vertebrate species than sites without colonies. Prairie dogs affect habitat for these species through multiple pathways, including creation of belowground refugia, supply of prey for specialized predators, modification of vegetation structure within colonies, and increased landscape heterogeneity.

Nest predation on black-tailed prairie dog colonies

Nest predation is the principal cause of mortaliv for many grassland birds. Predation rates may be higher on prairie dog colonies because they may have less available nesting cover and may increase predator abundance. We compared 14-day nest predation rates for 1,764 artificial nests on 102 black-tailed prairie dog (Cynovnys ludovicianus) colonies and their paired off-colony sites (similar habitat lacking prairie dogs) from 14 May to 26 June 1998 in South Dakota and Wyoming. Predation rates on colonies (66.2 t 2.2%; f t SE) were 29.5% higher than at off-colony sites (51.1 t 2.7%). Nesting cover on colonies was less dense and more uniform in structure and regression analysis showed differences in nest predation rates were correlated with estimates of mean nesting cover. Avian species associated with prairie dog colonies had smaller clutches and more broods/ year than species associated with off-colony sites, suggesting a mechanism that may help compensate for increased risk of nest failure. Factors that influence predator-prey dynamics (e.g., habitat fragmentation) or foraging success (e.g., insect availability) also may help explain higher risk of nest predation on prairie dog colonies. Our conclusions support others in recommending protection of large, intact prairie dog ecosystems. JOURNAL OF WILDLIFE MANAGEMENT 64(3):776-784

Predation of artificial ground nests on white-tailed prairie dog colonies

Prairie dog (Cyuomys spp. 1 colonies are unique to prairie and shrub-steppe landscapes However, widespread eradication, habitat loss, and sylvatic plague (Yersinia pestis) have reduced their numbers by 98% since historical times. Birds associated with prairie dogs also are declining. Potential nest predators, such as coyotes (Canis latrans), swift foxes (Vulpes velox), and badgers (Taxidea taxus), may be attracted to colonies where a high concentration of prairie dogs serve as available prey, Increased abundance of small manimals, including prairie dogs, also may increase the risk of predation for birds nesting on colonies. Finally, because grazing by prairie dogs may decrease vegetation height and canopy cover, bird nests may be easier for predators to locate. In this study we placed 1.444 artificial ground nests on and off 74 white-tailed prairie dog (C. leucurus) colonies to test the hypothesis that nest predation rates are higher on colonies than at nearby off sites (i.e., uncolonized habitat) We sampled colonies from 27 May to 16 July 1997 at the following 3 complexes: Covote Basin, Utah and Colorado: Moxa Arch, Wyoming; and Shirley Basin, Wyoming, Differences in daily predation rates between colonies and paired off sites averaged 1.0% ( P = 0.060). When converted to a typical 14-day incubation period, predation rates averaged 14% higher on colonies (57.7 ± 2.7%, x ± SE) than at off sites (50.4 ± 3.1%) Comparisons of habitat variables on colonies to off sites showed percent canopy cover of vegetation was similar (P = 0.114) percent bare ground was highe on colonies (P 0.288), Although we found the risk of nest predation was higher on hite-tailed prairie dog colonies than at off sites, fitness of birds nesting on colonies might depend on other factors that influence foraging success, reproductive success, or nestling survival.

Efficacy of Tail-Mounted Transmitters for Beaver

Abstract In 2001, I attached tail-mounted transmitters to 41 beaver (Castor canadensis) captured in Rocky Mountain National Park to evaluate if the transmitters (Rothmeyer et al. 2002) would be suitable to conduct long-term life history research. Twenty-one of the transmitters became detached from the tail without evidence of beaver mortality. I was unable to recover and determine the outcome for 9 transmitters because signals originated from the inside of active beaver lodges. Antennas were intact on 7 detached transmitters but were missing and likely chewed-off on 11 others. In conclusion, tail-mounted transmitters for beaver were of limited success in this life history study and are not recommended for long-term monitoring without significant modifications to the original design.

Competition favors elk over beaver in a riparian willow ecosystem

Beaver (Castor spp.) conservation requires an understanding of their complex interactions with competing herbivores. Simulation modeling offers a controlled environment to examine long-term dynamics in ecosystems driven by uncontrollable variables. We used a new version of the SAVANNA ecosystem model to investigate beaver (C. canadensis) and elk (Cervus elaphus) competition for willow (Salix spp.). We initialized the model with field data from Rocky Mountain National Park, Colorado, USA, to simulate a 4-ha riparian ecosystem containing beaver, elk, and willow. We found beaver persisted indefinitely when elk density was ≤20 elk km−2. Beaver persistence decreased exponentially as elk density increased from 30 to 60 elk km−2, which suggests the presence of an ecological threshold. The interaction of beaver and elk herbivory shifted the size distribution of willow plants from tall to short when elk densities were ≥30 elk km−2. The loss of tall willow preceded rapid beaver declines, thus willow condition may p...