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Inzunza E.R.,Pronatura Veracruz | Inzunza E.R.,Dartmouth College | Goodrich L.J.,Acopian Center for Conservation Learning | Hoffman S.W.,HawkWatch International Inc.
Bird Conservation International | Year: 2010

Continental-scale bird population estimates are used as a decision-support tool in conservation plans. The calculation of these estimates includes the use of density values and survey data from one or multiple sources extrapolated to the geographic scale of interest. In this paper, we use migration count data from a migration monitoring project in Veracruz, Mexico, to revise existing North American population estimates of seven species of waterbirds, New World vultures, and diurnal raptors. In two species of waterbirds, we suggest that existing estimates are low and propose a mechanism to correct these figures. In the remaining five cases, we also determine present estimates are low, but use our data to provide new continental-scale values. We discuss the importance of refining population estimates using data from a diverse suite of field methods as a means to overcome the limitations of the single-survey-based estimates. Copyright © BirdLife International 2009. Source

Farmer C.J.,Acopian Center for Conservation Learning | Smith J.P.,HawkWatch International Inc.
Journal of Raptor Research | Year: 2010

Long-term monitoring is important for ensuring effective conservation of raptor populations. Raptors also can serve as indicators of biodiversity and ecosystem condition. Therefore, effective monitoring of raptor populations yields the added benefit of helping to evaluate the status of ecosystems. Spring counts of migrating raptors at concentration points may contribute to these goals, particularly by providing insight into the vital demographic rates underlying population trends. Although much is known about the monitoring value of autumn migration counts in North America, little research has addressed the value of spring counts. We compared counts at seven spring watchsites to those at seven autumn watchsites matched by region (Southwest, Great Lakes, and Northeast) to assess the value of spring counts for population monitoring. Our analyses suggested that population indexes derived from spring migration counts provided estimates of population change that differed overall from autumn migration counts in the same region. The concordance of spring and autumn trends was higher in the Southwest and Northeast than in the Great Lakes region, suggesting greater variation in the seasonal representation of populations in the latter region. The average precision of spring trend estimates was better than for autumn estimates in the same region in two of three regions, and the estimated rates of change often were lower in spring. Spring counts enhanced the ability to estimate population trends for species that are less common in autumn counts, including the Rough-legged Hawk (Buteo lagopus) and Red-shouldered Hawk (B. lineatus). To realize fully the value of spring counts, we recommend the establishment of additional spring watchsites in areas that concentrate migrants in autumn, but do so to a lesser extent in spring, as well as additional research to define the populations sampled by autumn and spring counts. © 2010 The Raptor Research Foundation, Inc. Source

Freeman E.D.,Brigham Young University | Sharp T.R.,Brigham Young University | Larsen R.T.,Brigham Young University | Knight R.N.,U.S. Army | And 2 more authors.
PLoS ONE | Year: 2014

Exotic invasive species can directly and indirectly influence natural ecological communities. Cheatgrass (Bromus tectorum) is non-native to the western United States and has invaded large areas of the Great Basin. Changes to the structure and composition of plant communities invaded by cheatgrass likely have effects at higher trophic levels. As a keystone guild in North American deserts, granivorous small mammals drive and maintain plant diversity. Our objective was to assess potential effects of invasion by cheatgrass on small-mammal communities. We sampled small-mammal and plant communities at 70 sites (Great Basin, Utah). We assessed abundance and diversity of the small-mammal community, diversity of the plant community, and the percentage of cheatgrass cover and shrub species. Abundance and diversity of the small-mammal community decreased with increasing abundance of cheatgrass. Similarly, cover of cheatgrass remained a significant predictor of small-mammal abundance even after accounting for the loss of the shrub layer and plant diversity, suggesting that there are direct and indirect effects of cheatgrass. The change in the small-mammal communities associated with invasion of cheatgrass likely has effects through higher and lower trophic levels and has the potential to cause major changes in ecosystem structure and function. Source

Delong J.P.,Eagle Environmental Inc. | Delong J.P.,HawkWatch International Inc. | Delong J.P.,University of Nebraska - Lincoln | Cox N.S.,Rio Grande Bird Research Inc. | And 5 more authors.
Condor | Year: 2013

Prey selection of migrating raptors has been documented only rarely. Here we used a genetic approach to identify avian prey of Sharp-shinned Hawks (Accipiter striatus) migrating through central New Mexico. we identified species by comparing profiles of a section of the 16S rRNA mitochondrial gene extracted from feathers of prey of known species to profiles from feathers of prey found on the feet and beaks of migrating hawks. we also quantified prey availability along the migration route with multi-year sampling by mist net at two sites near the raptor-sampling site. Sharp-shinned Hawks took most prey species in proportion to their availability, but they took some species, particularly medium-sized species, more frequently than expected. This pattern may indicate selection for energetically rewarding prey, or the pattern also could arise from differences between our sample of potential prey and the potential prey as viewed by the hawks themselves. The co-occurrence of migrating predators and their prey suggests interesting feedbacks that likely influenced the evolution of migration strategies of both hawks and songbirds in this area. © The Cooper Ornithological Society 2013. Source

Paprocki N.,Boise State University | Paprocki N.,HawkWatch International Inc. | Glenn N.F.,Boise State University | Atkinson E.C.,Northwest College | And 2 more authors.
Journal of Wildlife Management | Year: 2015

There is widespread evidence that multiple drivers of global change, such as habitat degradation, invasive species, and climate change, are influencing wildlife. Understanding how these drivers interact with and affect species may be difficult because outcomes depend on the magnitude and duration of environmental change and the life history of the organism. In addition, various environmental drivers may be evaluated and managed at different spatial scales. We used a historical dataset from 1991 to 1994 and current information from 2010 to 2012 to examine whether occupancy patterns of wintering raptors were consistent with regional changes in distribution or habitat conditions within a local management unit, the Morley Nelson Snake River Birds of Prey National Conservation Area (NCA). We predicted that if local populations reflected regional shifts, then rates of raptor occupancy within the NCA would be higher compared to historical estimates and birds would use different habitats compared to historical use. Alternatively, if local populations were determined by habitat conditions, then we predicted that occupancy rate of raptors within the NCA would be lower compared to historical estimates and current habitat use would be consistent with historical use. Results support the hypothesis that northward distributional shifts influenced wintering raptor populations in southwest Idaho to a greater extent than local habitat conditions. Wintering raptors had higher occupancy rates in 2010-2012 compared to 1991-1994, whereas invasive grasses have increased and native shrubs have decreased suggesting that habitat suitability for raptors has declined over time. On the species level, changes in habitat use were associated with greater increases in occupancy rates in 2010-2012 compared to 1991-1994. Organisms flexible in their habitat use may be better able to respond to continental forces driving distribution shifts. Conversely, habitat or prey specialists may be poorly equipped to handle such rapid, large-scale global change. Further, Grinnellian niche models predicting species response to change by mapping current habitat use to forecasted vegetation maps should consider plasticity in habitat use and changes in the cost-benefits of life-history strategies. © 2015 The Wildlife Society. Source

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