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We revised distribution maps of potential presettlement habitat and current populations for Greater Sage-Grouse (Centrocercus urophasianus) and Gunnison Sage-Grouse (C. minimus) in North America. The revised map of potential presettlement habitat included some areas omitted from previously published maps such as the San Luis Valley of Colorado and Jackson area of Wyoming. Areas excluded from the revised maps were those dominated by barren, alpine, and forest habitats. The resulting presettlement distribution of potential habitat for Greater Sage-Grouse encompassed 1 200 483 km(2), With the species' current range 668 412 km(2). The distribution of potential Gunnison Sage-Grouse habitat encompassed 46 521 km(2), with...
Characterizing avian diet is complex, especially for generalist insectivores, as food resources can vary over space and time, and individuals of different sexes and ages may consume different food. We examined diet of a generalist insectivore, the Southwestern Willow Flycatcher (Empidonax traillii extimus), at Roosevelt Lake in central Arizona from 2000 to 2004, determined from 344 fecal samples. We found that five prey categories accounted for 70% of the proportional abundance in flycatcher diet: Hymenoptera, Diptera, Cicadellidae, Coleoptera, and Formicidae, although the relative amounts of these and other taxa differed significantly among years. We detected no differences in diet between sexes of adults, but...
We surveyed a discrete population of Mountain Plovers (Charadrius montanus) in South Park, Park County, Colorado, to determine the size and relative contribution of this geographically isolated area to the global population of plovers. First, we mapped potential plover habitat within South Park based on landform and vegetation descriptors. Second, we identified occupied habitat using observations from a systematic inventory of potential habitat from 1995-1999 and from a study of breeding biology from 2000-2002. Third, we estimated breeding densities within a framework designed specifically for distance sampling. We mapped 82750 ha of potential habitat. We recorded 2516 plover locations from which we estimated 29...
Anthropogenic changes in landscapes can favor generalist species adapted to human settlement, such as the Common Raven (Corvus corax), by providing new resources. Increased densities of predators can then negatively affect prey, especially rare or sensitive species. Jackson Hole and the upper Green River valley in western Wyoming are experiencing accelerated rates of human development due to tourism and natural gas development, respectively. Increased raven populations in these areas may negatively influence the Greater Sage-Grouse (Centrocercus urophasianus), a sensitive sagebrush specialist. We investigated landscape-level patterns in raven behavior and distribution and the correlation of the raven data with the...
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Adult movement and natal dispersal data demonstrate that Northern Goshawks (Accipiter gentilis) are able to travel over long distances, suggesting a large functional population. However, these data are unable to determine whether these movements contribute to gene flow among adjacent breeding areas. We used eight microsatellite DNA loci and mitochondrial DNA control-region sequence data to assess population structure of Northern Goshawks breeding in Utah. Goshawks had moderate levels of genetic variation at microsatellite loci (observed heterozygosity = 50%), similar to levels found in other medium-sized, highly mobile birds. Overall estimates of interpopulation variance in microsatellite alleles (FST = 0.011) and...
Degradation, fragmentation, and loss of native sagebrush (Artemisia spp.) landscapes have imperiled these habitats and their associated avifauna. Historically, this vast piece of the Western landscape has been undervalued: even though more than 70% of all remaining sagebrush habitat in the United States is publicly owned, <3% of it is protected as federal reserves or national parks. We review the threats facing birds in sagebrush habitats to emphasize the urgency for conservation and research actions, and synthesize existing information that forms the foundation for recommended research directions. Management and conservation of birds in sagebrush habitats will require more research into four major topics: (1) identification...
Although polygyny can potentially increase male reproductive success, the benefits of this strategy could be offset by losses to extra-pair paternity or reduced offspring survival. We developed microsatellite markers to assess the influence of extrapair offspring (EPO) on reproductive success and paternity in monogamous and polygynous pairs of the facultatively polygynous Southwestern Willow Flycatcher (Empidonax traillii extimus). Based on genotypes of 140 offspring from 56 clutches over six years, 14% of nestlings in our study population were extra-pair offspring, with 23% of all successful nests containing at least one EPO. We found that polygynous males produced 2.11 0.35 offspring per season, compared to 1.15...
We contextually analyzed the song of the Bobolink (Dolichonyx oryzivorus) to examine the role of sexual selection on song versatility. Recordings were obtained as territorial males were randomly presented with a caged male (a conspecific intruder), a caged female (a potential breeding partner), and an empty control cage. Sound spectrograms created from the recordings were analyzed and an index of versatility was calculated for each male in each manipulation so that individual song variation could be compared among behavioral contexts. These analyses suggest that more complex or versatile song production is being selected intersexually, whereas short repetitive song is intrasexually selected. Published in The Condor,...


    map background search result map search result map Gene flow and genetic characterization of Northern goshawks breeding in Utah Distribution of Sage-Grouse in North America Gene flow and genetic characterization of Northern goshawks breeding in Utah Distribution of Sage-Grouse in North America