Food habits and nest characteristics of breeding raptors in southwestern Wyoming

Food habits and nest site features of the Golden Eagle ( Aquila chrysaetos ), Prairie Falcon ( Falco mexicanus ), Red-tailed Hawk ( Buteo jamaicensis ), and Ferruginous Hawk ( B. regalis ) were studied near Medicine Bow, Wyoming, during 1981 and 1982. Foods consisted primarily of leporids and sciurids. The Wyoming ground squirrel ( Spemiophilus richardsonii ) dominated the diet of Prairie Falcons, while Golden Eagles preyed on leporids more than did the other raptors. Diet overlap ranged from 59 to 99% between the species. Mean height of Golden Eagle nests was greater than nest height of other species. Most raptor nests (78%) were not visible from other active nests and were in view of roads. Prairie Falcons were the most specialized and Ferruginous Hawks the most versatile raptor species in terms of food habits and use of nest sites.     

Breeding populations of Swainson's Hawks, Red-Tailed Hawks, and Golden Eagles in north central Oregon: 1975-1982 and 1999

Populations of breeding Swainson's Hawks ( Buteo swainsoni ), Red-tailed Hawks ( B. jamaicensis ), and Golden Eagles ( Aquila chrysaetos ) present in 1999 were compared with populations present between 1975 and 1982 at a 129-km 2 site in north central Oregon. Populations of Red-tailed Hawks and Golden Eagles remained unchanged, but the number of Swainson's Hawks pairs increased from 15 to 17. In 1999 Golden Eagles used nests occupied between 1975 and 1982, and 7 of 31 pairs of Red-tailed Hawks used nests occupied in earlier years. No Swainson's Hawks nested in trees occupied earlier. Few changes in territorial boundaries were detected.     

Winter survey of raptors with notes on avian scavengers in northwestern Colorado

Winter populations of raptors and scavengers were surveyed along 175 km of rural roads in Moffat County, northwestern Colorado. The survey began in 1988 and is currently continuing. Over the 7 yr of the survey reported here, we found Golden Eagles in high abundance (￣ x = 5.8 km/eagle) compared to most studies in similar habitat. Bald Eagles were less abundant, but increasing compared to 20 yr earlier. American Rough-legged Hawks were in low abundance, probably due to the predominance of sagebrush habitat along the route. Northern Ravens were seen in low numbers in 4 yr. American Crows were seen in 2 yr. Black-billed Magpies were nearly as abundant (￣ x = 6.5 km/magpie) as Golden Eagles and often scavenged with them. Magpie and Golden Eagle numbers were significantly correlated over the years of study. We conclude that northwestern Colorado is a significant overwintering area for Golden Eagles.     

Habitat and spatial relationships of nesting Swainson's Hawks ( Buteo swainsoni ) and Red-tailed Hawks ( B. jamaicensis ) in northern Utah

A total of 28 Swainson's Hawk ( Buteo swainsoni ) and 30 Red-tailed Hawk ( B. jamaicensis ) nests were found in Cache Valley, Utah, during the summers of 1992 and 1993. All nests were in trees, but only Red-tailed Hawks nested in dead trees (30%). In the intensive study area, nesting densities were 0.10 nests/km 2 for Swainson's Hawk and 0.08 nests/km 2 for Red-tailed Hawk. Nearest-neighbor nest distances were significantly shorter among Swainson's Hawks (1.74 km) than among Red-tailed Hawks (2.83 km). Congeneric nearest-neighbor distances were significantly shorter than conspecific distances for Red-tailed Hawks (1.59 vs 2.83 km) but not for Swainson's Hawks (1.52 vs. 1.74). GIS analysis of habitat types was made for 2-km radii around nest sites. Cropland was the dominant land cover type at nest sites of both species and no significant difference was found between species. Swainson's Hawk nest sites contained significantly more pasture, whereas Red-tailed Hawk nest sites contained significantly more juniper, maple, and sagebrush. Only Red-tailed Hawk nests ( n = 8; 27%) were found on the periphery of the valley at the base of foothills of the Cache Mountains. This preference resulted in a significantly higher elevation for Red-tailed Hawk nest sites. Swainson's Hawk nests occurred only on the valley floor on level terrain. Distance to the nearest paved road and building was very similar for both species, implying that little difference exists in tolerance levels for human activities. Overall, multivariate niche overlap for habitat was high (0.89), indicating a lack of habitat partitioning between these 2 Buteos in Cache Valley.     

Response of wintering buteos to plague epizootics in prairie dogs

Several species of raptors winter at Rocky Mountain Arsenal National Wildlife Refuge (Refuge) including the Bald Eagle ( Haliaeetus leucocephalus ), Ferruginous Hawk ( Buteo regalis ), Red-tailed Hawk ( Buteo jamaicensis ), and Rough-legged Hawk ( Buteo lagopus ). Raptors were monitored each winter from 1988-89 to 1996-97 using a standardized road survey. Black-tailed prairie dogs ( Cynomys ludovicianus ) form a major component of the prey base for wintering raptors on the Refuge, with 1850 ha of active prairie dog towns mapped in 1988. Prairie dog town areas and population data were determined by mapping active towns and conducting visual counts on study plots to determine population density on an annual basis from 1988 to 1996. Large-scale plague epizootics were documented on the Refuge in 1988-89 and 1994-95, reducing prairie dog towns by 95% and 99%, respectively. A significant relationship was found in the numeric response of Ferruginous Hawks to changes in prairie dog town area ( r 2 = 0.96, P r 2 = 0.97, P r 2 = 0.07, P = 0.486). This contrasted sharply with the responses to prairie dog town area found for Red-tailed ( r 2 = 0.11, P = 0.377) and Roughlegged Hawks ( r 2 = 0.04, P = 0.612).     

Maternal defensive behavior of mountain goats against predation by golden eagles

Maternal defensive behavior against predators may appear risky but is common in many species. Herein we describe maternal defensive behavior of mountain goats ( Oreamnos americanus ) against Golden Eagle ( Aquila chrysaetos ) predatory attempts. We found that Golden Eagles attacked goats in 1.9% of sightings ( n = 311 sightings of active Golden Eagles over 12 years) but were never successful. Mothers always defended their young against Golden Eagle attacks. Predation by Golden Eagles on young-of-the-year appears low for most ungulate species, including mountain goats. The benefits of defending offspring against eagles are likely high in ungulates, and we would therefore expect selection to favor maternal defensive behavior.     

Breeding birds at the Idaho National Engineering and Environmental Laboratory, 1985-1991

During the summers of 1985-1991, bird census were conducted along 13 permanent routes located at the 2315-km 2 Idaho National Engineering and Environmental laboratory (INEEL Sturnella neglecta ), Brewer's Sparrows ( Spizella breweri ), Sage Sparrows ( Amphispiza belli ), Horned larks ( Eremophila alpestris ), and Sage Thrashers ( Oreoscoptes montanus ) comprised 72% of all individuals. Almost half of all species were represented by fewer than 10 individuals. Bird density was significantly greater along facility complex routes. Moreover, because of human-constructed wetlands and structures of various types, facility complex routes had significantly more bird species per unit area, including more species of waterfowl and human associated species. Some year-to-year variation in bird density was related to weather. More individuals were recorded in cooler, wetter years, although such increases were reflected more along facility complex routes. Among sagebrush-obligate species, trend analysis suggest that both Brewer's Sparrows and Sage Sparrows increased significantly in abundance, which may be in contrast to regional trends for these species. Of 5 species of special concern observed, trend analysis could be performed for only 2: Ferruginous Hawks ( Buteo regalis ) and Loggerhead Shrikes ( Lanius ludovicianus ). Both species had more routes with negative regression coefficients and negative trend means, indicating that declines may have occurred, although the goodness-of-fit test for neither species was significant. These data from INEEL should be used for comparison with future studies at the site and other statues from throughout the Great Basin region.     

Grazing and passerine breeding birds in a Great Basin low-shrub desert

Densities of passerine breeding birds were compared between four range pastures variously grazed by sheep over a 50-year period. The experimental pastures, located at the Desert Experimental Range in southwestern Utah, included three grazed and one ungrazed. Grazed pastures were each heavily stocked and grazed annually at one of three winter seasons (early, middle, or late). Important structural (physiognomic) and compositional differences existed in the vegetation of the experimental pastures. Horned Larks ( Eremophila alpestris [Linnaeus]), numerically dominant in the pastures, apparently responded to those differences. Black-throated Sparrows ( Amphispiza bilineata [Cassin]) and Loggerhead Shrikes ( Lanius ludovicianus Linnaeus) were less common and found as breeding birds only in dry wash habitats. No significant differences were found between the pastures in estimates of total breeding bird populations, bird standing crop biomass, or bird species richness.     

Predator-specific mortality of pronghorn on Yellowstone’s northern range

Yellowstone National Park supports a small population ( Antilocapra americana ). Some individuals migrate during summer to areas characterized by reduced visibility, mixed habitat types, and a diverse predator community. Across areas selected by migratory and nonmigratory pronghorn, we documented cause-specific mortality of adults and fawns and assessed relative risk of predation by various predators. Coyotes ( Canis latrans ) accounted for 56% of adult predation and up to 79% of fawn predation. Cougars ( Puma concolor ) and wolves ( Canis lupus ) accounted for additional predation of adults, while cougars, black bears ( Ursus americanus ), and Golden Eagles ( Aquila chrysaetos ) were documented killing fawns on rare occasions. Our results suggest that even when pronghorn are in the presence of multiple predator species, coyote predation on adults and fawns may predominate for populations inhabiting shrubsteppe habitat. However, the risk of predation by sympatric predators, particularly cougars, may be high for female pronghorn selecting mixed cover types during migration or for birthing purposes. While the direct effect of wolves on overall mortality was low, wolves may indirectly influence survival rates of adult females and fawns by altering the behavior and space use of sympatric predators, particularly coyotes.     

Bald eagle winter survey in the Snake River Canyon, Wyoming

A 5-year winter bald eagle survey was conducted along 22 km of the Snake River Canyon in northwestern Wyoming. Surveys were done on 94 days requiring 1,414 hrs and 1,888 km driving. In all, 220 (85 percent adults) bald eagles were seen. Seventy-seven percent of all eagles were perching, 15 percent were flying, 4 percent were feeding on road-killed mule deer, and 4 percent were flying low over water. Perching sites were identified as 32 percent cottonwoods, 30 percent spruce, 17 percent Douglas-fir, and 22 percent other. Eagles were somewhat clumped in distribution.     

Food of cougars in the Cascade Range of Oregon

Animal and nonanimal items were identified in the digestive tracts of 61 cougars ( Felis concolor ) collected between 1978 and 1984 from the western slopes of the Cascade Range in Oregon. Forty - two (69%) of the cougars were taken by hunters in December and January, 18 (30%) were killed at other times of the year because of their proximity to livestock, and one animal was illegally killed in November. Black-tailed deer ( Odocoileus hemionus columbianus ) was the most common prey item, although domestic sheep ( Ovis airies ), porcupines ( Erethizon dorsatum ), and a variety of small mammals were also recorded. Masticated grass was the most common nonanimal item.      

Mule deer and pronghorn use of wastewater ponds in a cold desert

Pronghorn ( Antilocapra americana ) and mule deer ( Odocoileus hemionus ) were counted at wastewater ponds at the Idaho National Engineering and Environmental Laboratory (INEEL) in southeastern Idaho 4 to 8 times per month from August 1989 through July 1991. Mule deer used wastewater ponds ( n = 15) from June through December and were most commonly observed August through November. Pronghorn frequented wastewater ponds from May through November and were most common from July through September, the driest and warmest months; ponds were also used heavily in November 1990. Diel activity was studied from July through October. Mule deer use of ponds varied in relation to 8 diel time periods in August ( P = 0.02) and September ( P = 0.01) while pronghorn use varied by time period ( P P P < 0.01) August through October. Mule deer and pronghorn use of ponds was not related to distance from site facilities (groups of buildings used for research and other purposes). Pronghorn made greater use of individual ponds lacking additional nearby watering sites, and both pronghorn and mule deer were attracted to ponds with grass/forb and shrub cover around the upland periphery.     

Species composition and relative abundance of adult fish in Pyramid Lake, Nevada

Pyramid Lake fish populations were sampled with nets on a monthly basis from November 1975 through December 1977. Fish species were taken in the following order of numerical relative abundance: tui chub ( Gila bicolor ), Tahoe sucker ( Catostomus tahoensis ), Lahontan cutthroat trout ( Salmo clarki henshawi ) including cutthroat-rainbow hybrids, cui-ui ( Chasmistes cujus ), and Sacramento perch ( Archoplites interruptus ). Relative abundance estimates are discussed with respect to seasonal availability, spatial distribution of the fish, sampling bias of the fishing methods, and biomass of the fish. Recent temporal trends in the population structure of the lake are presented.     

Temperature and salinity relationships of the Nevadan relict dace

Pyramid Lake fish populations were sampled with nets on a monthly basis from November 1975 through December 1977. Fish species were taken in the following order of numerical relative abundance: tui chub ( Gila bicolor ), Tahoe sucker ( Catostomus tahoensis ), Lahontan cutthroat trout ( Salmo clarki henshawi ) including cutthroat-rainbow hybrids, cui-ui ( Chasmistes cujus ), and Sacramento perch ( Archoplites interruptus ). Relative abundance estimates are discussed with respect to seasonal availability, spatial distribution of the fish, sampling bias of the fishing methods, and biomass of the fish. Recent temporal trends in the population structure of the lake are presented.     

Reproductive cycle of the lizard Sceloporus mucronatus with comments on intraspecific geographic variation

Sceloporus mucronatus is a viviparous lizard that inhabits high altitudes in central M&eacute;xico. Lizards from Tecocomulco, Hidalgo, M&eacute;xico, were collected monthly at 2500 m throughout one year. Macro- and microscopic evidence of gonads showed that both sexes reproduce synchronously during the fall. In males, after a short testicular quiescence in December, the recrudescence begins in winter (January) and continues through spring and summer (July), with maximum activity occurring from late summer to early fall (August&ndash;September). Regression takes place simultaneously with copulation during the fall (October&ndash;November). In females, vitellogenesis occurs during summer and fall (August&ndash;November), with ovulation in the fall (November&ndash;December). Gravid females were found throughout the winter, and parturition occurs during spring (May). Litter size was correlated with female snout&ndash;vent length. Female reproductive phenology of viviparous Sceloporus species seems to be highly conservative at different altitudes, but male reproductive phenology shifts between spring&ndash;summer (in populations higher than 2500 m) and summer&ndash;fall (in populations 2500 m or lower), as in the present study. The longer period of testicular recrudescence (January&ndash;July) in the studied population from Tecocomulco suggests plasticity in testicular activity.     

Successful nesting by a Bald Eagle pair in prairie grasslands of the Texas Panhandle

We observed a breeding Bald Eagle ( Haliaeetus leucocephalus ) pair nesting in a short-grass prairie and agricultural community on the southern Great Plains of the Texas Panhandle in 2004 and 2005. The nesting eagles produced 1 fledgling in 2004 and 2 fledglings in 2005. Our assessment of landcover types within a 5-km radius of the nest indicated that grasslands accounted for most of the area (90%), followed by agricultural lands (8%). Black-tailed prairie dog ( Cynomys ludovicianus ) colonies occupied 2.5% of the area, and single human residences with associated structures (i.e., barns) occupied 2.5 ha in surface area was 51 km from the nest. An analysis of regurgitated castings collected near the nest revealed a mammalian-dominated, breeding-season diet with black-tailed prairie dogs occurring in 80.9% of the castings. Other identified prey included cottontails ( Sylvilagus spp., 15.9%), black-tailed jackrabbits ( Lepus californicus , 3.2%), pronghorn ( Antilocapra americana , 3.2%), and plains pocket gopher ( Geomys bursarius , 1.6%). Bird remains were also present in 34.9% of the castings. This is the first reported successful nesting of Bald Eagles in the panhandle region of Texas since 1916; the nest is particularly unique because of its distance from any substantial body of water.     

Terrestrial vertabrates of Scotts Bluff National Monument, Nebraska

A survey of terrestrial vertebrates was conducted at the Scotts Bluff National Monument (SBNM), Nebraska, to determine species composition, relative abundance, and distribution by habitat of the existing amphibians, reptiles, birds, and mammals. Various sampling methods were used to detect animal species richness and to estimate population densities. The seven major habitat types at SBNM contained 4 species of amphibians, 8 reptiles, 96 birds, and 28 mammals. The only endangered or threatened species observed was a dead bald eagle ( Haliaeetus leucocephalus ). The racer ( Coluber constrictor ) and prairie rattlesnake ( Crotalus viridis ) were the two most abundant snakes. The prairie falcon ( Falco mexicanus ) was a common raptor that nested in Scotts Bluff. Sympatric populations of mule deer ( Odocoileus hemionus ) and white-tailed deer ( Odocoileus virginianus ) appeared to be hybridizing. The riverine woodland contained the greatest number of fauna species with only 4% surface area of SBNM. Sharp-tailed grouse ( Tympanuchus phasianellus ) and pronghorn antelope ( Antilocapra americana ), absent from the Monument, are two potential native species for reintroduction.     

Winter and early spring bird communites in grasslands, shrubsteppe, and juniper woodlands in central Oregon

We compared winter (December, January, and February) and early spring (March and April) bird communities among 4 successional stages that included grassland, shrubsteppe, juniper-shrubsteppe, and old-growth juniper woodland in central Oregon. Birds were surveyed monthly from December through April in 1998/1999 and 1999/2000 using the point count method to estimate relative abundance of birds (individuals ? transect –1 year –1 ). We used distance sampling to correct for potential bias in estimating abundance and density among successional stages. A total of 4513 birds (32 species) were detected. Relative abundance of total birds (all species combined) was similar in the juniper-shrubsteppe and old-growth woodland (48.7 and 48.9 individuals ? transect –1 , respectively) but 6 times greater than in the grassland and shrubsteppe (8.0 and 7.7 individuals ? transect –1 , respectively) during the 5-month period. Total density of birds was greater in old-growth juniper woodland and juniper-shrubsteppe than in grassland or shrubsteppe. However, median bird species richness in 1998/1999 was highest in grassland and lowest both in shrubsteppe and juniper-shrubsteppe, and in 1999/2000 it was highest in shrubsteppe and lowest in juniper-shrubsteppe and oldgrowth juniper woodland. American Robins and Townsend's Solitaires were the most abundant species in junipershrubsteppe and old-growth juniper woodland during the winter months. Sage Sparrows and Horned Larks were the most abundant species in shrubsteppe during winter, and Horned Larks were most abundant in grasslands during the early spring transition period prior to nesting. Our results indicate that a different suite of species use these successional stages during the nonbreeding season. If avifauna conservation is a part of long-term management goals, a broad range of successional stages should be maintained on the landscape to provide habitat for a variety of avian species throughout the year.     

Effects of habitat type and degradation on avian species richness in Great Basin riparian habitats

The overwhelming majority of bird species in the Great Basin region are found in riparian habitats. However, most previous research on the impact of change in habitat condition through degradation on these bird communities failed to account for the large intersite differences, in both habitat type and extent of degradation. We examined songbird communities in 4 riparian habitat types (meadows, willow-birch-, and aspen-dominated forest stands) during summers 1994 (last year of a 7-yr drought) and 1995 (following the 6th wettest winter recorded) in the Toiyabe Mountain Range of central Nevada. Habitat degradation significantly influenced bird species richness in riparian areas, but the impact was dependent upon habitat type. While meadow bird communities were affected adversely by habitat degradation, with significant drops in species richness on degraded sites, bird species richness in forested riparian habitats was consistently greater on degraded sites. Data for the 6 most common species seen during our study indicated that degradation may have influenced distribution of American Robins ( Turdus migratorius ) and Yellow Warblers ( Dendroica petechia ), but habitat type was the best predictor of abundance for House Wrens ( Troglodytes aedon ), Red-naped Sapsuckers ( Sphyrapicus nuchalis ), Warbling Vircos ( Vireo gilvus ), and Brewer's Blackbirds ( Euphagus cyanocephalus ). Avian species diversity in meadow habitats may be linked to moisture levels during specific times of the year. Diversity increased during the pre-migratory period of the dry year (1994) when compared with that of the breeding season, but was unchanged in the wet year (1995).