Geology topics

Diego R. Johnson

Publications and source records attributed to Diego R. Johnson.

3 recordsLinked to original sources

USGS2017

Common Raven ( Corvus corax ) kleptoparasitism at a Golden Eagle ( Aquila chyrsaetos ) nest in southern Nevada

The Common Raven ( Corvus corax ) is a ubiquitous species in the Mojave Desert of southern Nevada and California. From 5 to 24 May 2014, using remote trail cameras, we observed ravens repeatedly kleptoparasitizing food resources from the nest of a pair of Golden Eagles ( Aquila chyrsaetos ) in the Spring Mountains of southern Nevada. The ravens fed on nine (30%) of the 30 prey items delivered to the nest during the chick rearing period. Kleptoparasitic behavior by the ravens decreased as the eagle nestling matured to seven weeks of age, suggesting a narrow temporal window in which ravens can successfully engage in kleptoparasitic behavior at eagle nests. The observation of kleptoparasitism by Common Ravens at the nest suggests potential risks to young Golden Eagles from Common Ravens.

Nevada↗

USGS2017

An assessment of food habits, prey availability, and nesting success of golden eagles within the Desert Renewable Energy Conservation Plan Area

Within the Desert Renewable Energy Conservation Plan area, which encompasses California’s Mojave Desert, development and operation of renewable energy facilities has the potential to impact golden eagle (Aquila chrysaetos) populations through loss of habitat and prey base. Developing an effective conservation strategy that aims to mitigate for such operations is necessary to lessen these impacts; however, this requires site-specific knowledge of how golden eagle productivity is influenced by variability in prey abundance. In this study, researchers studied the food habits, prey availability, and nesting success of golden eagles in the conservation plan area over two seasons (2014 and 2015). In addition, as part of a collaborative research effort funded by the U.S. Fish and Wildlife Service, the same research was conducted within the adjoining Mojave Desert ecoregion of southern Nevada; these research results are presented as well. To examine prey availability, researchers conducted nocturnal spotlight surveys along 140 fivekilometer transects. Diet selection was determined using motion-activated trail cameras and by collecting prey remains at 20 active nests. Nesting success was determined by conducting occupancy and reproductive assessment surveys within 50 historic breeding areas and evaluating camera data collected at active nests. Preliminary results indicate high spatial variability in prey species abundance and selection. Black-tailed jackrabbits (Lepus californicus) represented over half the available prey, as well as nearly half the prey species identified by nest cameras. Overall, nesting success was 47 percent. Productivity was 0.67 young per occupied breeding area, and mean brood size was 1.4 young per successful nest. No evidence was found indicating that camera installation caused nest failures or influenced eagle behavior for any sites. Results from this project are incorporated into a spatial demographic model linking prey availability and abundance to golden eagle productivity across a changing Mojave Desert landscape.

Report↗

USGS2015

Habitat selection and survival of pronghorn fawns at the Carrizo Plain National Monument, California

On the Carrizo Plain National Monument (CPNM), California, little is known about survival rates and habitat characteristics of pronghorn fawns (Antilocapra americana). A marked decline in pronghorn numbers on the CPNM (from approximately 200 to <30 individuals from 1989 to 2011) prompted a study of fawn habitat use and fawn survival from 2009 to 2011. Only 45 fawns were born during this period. We attached GPS collars to 44% of these fawns (<5 days-of-age). We then used the locations of collared fawns to develop two separate binary logistic regression models to explore the best combination of micro- and macrohabitat-scale environmental variables for predicting (1) fawn habitat selection and (2) fawn survival. Model results for habitat selection showed that fawn locations were associated with increased concealment at close distances (5 m and 50 m) and decreased concealment at far distances (100 m). Fawn locations were on lower sloped terrain and closer to available drinking water and saltbush (Atriplex spp.). Model results for fawn survival showed that increased survival time was associated with higher sloped terrain, proximity to available drinking water and saltbush, and increased distance from high-use roads. Collectively, these results demonstrate that fawn habitat selection is scale-dependent and likely influenced by the combined spatio-temporal needs of both females and their young. The results of this study can be used to inform critical management actions on the CPNM.

California↗