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At least 73 records · Page 4Linked to original sources
USGS2013

Nesting habitat and productivity of Swainson's Hawks in southeastern Arizona

We studied Swainson's Hawks ( Buteo swainsoni ) in southeastern Arizona to assess the status of the local breeding population. Nest success (≥1 young fledged) was 44.4% in 1999 with an average of 1.43 ± 0.09 (SE) young produced per successful pair. Productivity was similar in 2000, with 58.2% nesting success and 1.83 ± 0.09 fledglings per successful pair. Mesquite ( Prosopis velutina ) and cottonwood ( Populus fremontii ) accounted for >50% of 167 nest trees. Nest trees were taller than surrounding trees and random trees, and overall there was more vegetative cover at nest sites than random sites. This apparent requirement for cover around nest sites could be important for management of the species in Arizona. However, any need for cover at nest sites must be balanced with the need for open areas for foraging. Density of nesting Swainson's Hawks was higher in agriculture than in grasslands and desert scrub. Breeding pairs had similar success in agricultural and nonagricultural areas, but the effect of rapid and widespread land-use change on breeding distribution and productivity continues to be a concern throughout the range of the species.

Arizona↗
USGS2013

Interactions between a group of Golden Eagles and a herd of North American elk

Raptors are generally considered solitary predators (Schoener 1969), but occasionally they interact socially (Brown and Amadon 1968). Certain raptor species (e.g., Swallow-tailed Kites [ Elanoides forficatus ] and Swainson's Hawks [ Buteo swainsoni ]) concentrate in aggregations in response to localized, abundant food sources (Ellis et al. 1993). Many raptor species engage in group hunting (Ellis et al. 1993), and social foraging is a routine strategy for some species (e.g., Harris's Hawks [ Parabuteo unicinctus ]; Bednarz 1988, Ellis et al. 1993]. Raptors generally engage in group hunting to pursue elusive or large prey (Ellis et al. 1993). Occasionally individuals of conspecific raptors engage in play as a group sometimes involving chases of prey species (Palmer 1988). In this letter, we report interactions between a large group of Golden Eagles and a herd of adult and juvenile Rocky Mountain elk ( Cervus canadensis nelsoni ) in late autumn.

Idaho↗
USGS2014

The spring migration of adult North American Ospreys

Most North American Ospreys ( Pandion haliaetus ) are migratory, breeding in northern latitudes and migrating long distances to and from their wintering grounds in the tropics. Although fall migration patterns of North American Ospreys have been described and studied, very little has been published about the spring migration of these birds. We used satellite telemetry to: (1) determine the characteristics (timing, duration, migratory routes) of spring migrations of Ospreys; (2) determine if differences in spring migration patterns existed between sexes and among three breeding populations (east coast, midwestern, and western); and (3) compare consecutive fall and spring migrations of individual Ospreys. The median dates for departure from the wintering grounds and arrival on the breeding grounds did not differ significantly between adult male and female Ospreys. Compared to their fall migrations, all male and all east coast Ospreys spent fewer days on migration, fewer days in stopover periods along the migration route, traveled shorter distances overall, and traveled farther (on average) each day during spring. In contrast, fall and spring migration characteristics of all female and western Ospreys were similar. Our findings suggest that, although sex and breeding location might influence the spring migration strategy used by individual Ospreys, both males and females minimize the time spent on migration to ensure a timely arrival on the breeding grounds to establish or defend a nesting territory.

Journal of Raptor Research↗
USGS2015

Wintering Bald Eagle count trends in the conterminous United States, 1986–2010

We analyzed counts from the annual Midwinter Bald Eagle Survey to examine state, regional, and national trends in counts of wintering Bald Eagles ( Haliaeetus leucocephalus ) within the conterminous 48 United States from 1986 to 2010. Using hierarchical mixed model methods, we report trends in counts from 11 729 surveys along 844 routes in 44 states. Nationwide Bald Eagle counts increased 0.6% per yr over the 25-yr period, compared to an estimate of 1.9% per yr from 1986 to 2000. Trend estimates for Bald Eagles were significant ( P ≤ 0.05) and positive in the northeastern and northwestern U.S. (3.9% and 1.1%, respectively), while trend estimates for Bald Eagles were negative ( P ≤ 0.05) in the southwestern U.S. (−2.2%). After accounting for potential biases resulting from temporal and regional differences in surveys, we believe trends reflect post-DDT recovery and subsequent early effects of density-dependent population regulation.

Journal of Raptor Research↗
USGS2017

Seasonal movements of the Short-eared Owl (Asio flammeus) in western North America as revealed by satellite telemetry

The Short-eared Owl ( Asio flammeus ) is a widespread raptor whose abundance and distribution fluctuates in response to the varying amplitudes of its prey, which are predominately microtines. Previous efforts to describe the seasonal movements of Short-eared Owls have been hindered by few band recoveries and the species' cryptic and irruptive behavior. We attached satellite transmitters to adult Short-eared Owls at breeding areas in western and interior Alaska in June 2009 and July 2010, and tracked their movements for up to 19 mo. Owls initiated long-distance southward movements from Alaska and most followed a corridor east of the Rocky Mountains into the Prairie provinces and Great Plains states. Four owls followed a coastal route west of the Rocky Mountains, including one owl that crossed the Gulf of Alaska. Completed autumn migration distances ranged from 3205–6886 km (mean = 4722 ± 1156 km [SD]). Wintering areas spanned 21° of latitude from central Montana to southern Texas, and 24° of longitude from central California to western Kansas. Subsequent seasonal migrations were generally northward in spring and southward in autumn; these movements were comparatively short-distance (mean = 767.5 ± 517.4 km [SD]) and the owls exhibited low site fidelity. The Short-eared Owls we tracked from two relatively local breeding areas in Alaska used a patchwork of diverse open habitats across a large area of North America, which highlights that effective conservation of this species requires a collaborative, continental-scale focus.

Journal of Raptor Research↗
USGS2016

Use of noninvasive genetics to assess nest and space use by white-tailed eagles

Movement and space use are important components of animal interactions with the environment. However, for hard-to-monitor raptor species, there are substantial gaps in our understanding of these key determinants. We used noninvasive genetic tools to evaluate the details of space use over a 3-yr period by White-tailed Eagles ( Haliaeetus albicilla ) at the Naurzum Zapovednik in northern Kazakhstan. We genotyped, at 10 microsatellite markers and one mitochondrial marker, 859 eagle feathers and assigned naturally shed feathers to individuals. We identified 124 White-tailed Eagles, including both members of 5–10 pairs per year, and were able to monitor birds across years. Distances between eagle nests and hunting perches were always greater than nearest neighbor distances, eagles never used the closest available hunting perch, and hunting perches were always shared with other eagles. When eagles switched nests between years, the nests they chose were almost always well outside the space that theory predicted they defended the prior year. Our data are inconsistent with classical territorial and colonial models of resource use; they more closely resemble semi-colonial behavior. It is unlikely that standard methods of animal tracking (e.g., marking and telemetry), would have provided a similarly cost-effective mechanism to gain these insights into spatial and temporal aspects of eagle behavior. When combined with existing information on space use of other local species, these data suggest that partitioning of spatial resources among White-tailed Eagles and other eagles at the Zapovednik may be facilitated by the alternative strategies of space use they employ.

Naurzum Zapovednik↗
USGS2017

Species composition, timing, and weather correlates of autumn open-water crossings by raptors migrating along the East-Asian Oceanic Flyway

Raptor migration rarely involves long-distance movements across open oceans. One exception occurs along the East-Asian Oceanic Flyway. We collected migration data at two terrestrial hawkwatch sites along this flyway to better understand open-ocean movements along this largely overwater corridor. At the northern end of the Philippines, at Basco on the island of Batan, we recorded 7587 migratory raptors in autumn 2014. Near the southern end of the Philippines, at Cape San Agustin on the island of Mindanao, we recorded 27,399 raptors migrating in autumn 2012. Chinese Sparrowhawks ( Accipiter soloensis ) were the most common raptors observed, making up approximately 89% and 92% of total records for Basco and Cape San Agustin, respectively. The Grey-faced Buzzard ( Butastur indicus ) was the second most common raptor migrant, accounting for 8% of the total counts at both watch sites. The migration period was about 1–2 wk earlier at Basco, the more northerly site, than at Cape San Agustin. Overwater flights at Basco peaked in both the morning and late afternoon, whereas at Cape San Agustin there was only a morning peak. In general, the rate of migration passage at both sites was highest with clear skies when winds were blowing from the northwest. However, we observed interspecific differences in migration behavior at both sites, with Accipiters more likely to be observed with tailwinds and eastward winds, and Grey-faced Buzzards more likely observed with headwinds. These results help to characterize poorly known aspects of raptor biology and to identify potential migratory bottlenecks or key sites for raptor conservation in little-studied Philippine tropical ecosystems.

Journal of Raptor Research↗
USGS2018

Raptor interactions with wind energy: Case studies from around the world

The global potential for wind power generation is vast, and the number of installations is increasing rapidly. We review case studies from around the world of the effects on raptors of wind-energy development. Collision mortality, displacement, and habitat loss have the potential to cause population-level effects, especially for species that are rare or endangered. The impact on raptors has much to do with their behavior, so careful siting of wind-energy developments to avoid areas suited to raptor breeding, foraging, or migration would reduce these effects. At established wind farms that already conflict with raptors, reduction of fatalities may be feasible by curtailment of turbines as raptors approach, and offset through mitigation of other human causes of mortality such as electrocution and poisoning, provided the relative effects can be quantified. Measurement of raptor mortality at wind farms is the subject of intense effort and study, especially where mitigation is required by law, with novel statistical approaches recently made available to improve the notoriously difficult-to-estimate mortality rates of rare and hard-to-detect species. Global standards for wind farm placement, monitoring, and effects mitigation would be a valuable contribution to raptor conservation worldwide.

Journal of Raptor Research↗
USGS2017

No substitute for survival: Perturbation analyses using a Golden Eagle population model reveal limits to managing for take

Conserving populations of long-lived birds of prey, characterized by a slow life-history (e.g., high survival and low reproductive output), requires a thorough understanding of how variation in their vital rates differentially affects population growth. Stochastic population modeling provides a framework for exploring variation in complex life histories to better understand how environmental and demographic variation within individual vital rates affects population dynamics. Specifically, we used life-stage simulation analysis (LSA) to identify those life-history characteristics that most affect population growth and are amenable to management actions. The Golden Eagle ( Aquila chrysaetos ) is a wide-ranging raptor of conservation concern, which has been adopted as a focal species for conservation planning. Golden Eagle population trends in western North America currently appear stable. Yet an expanding human footprint that may increase mortality stimulated our investigation into the ability of populations to sustain reduced survival. We fit mixed-effects models to published estimates of vital rates to estimate the mean and process variation of productivity (young fledged per pair) and survival for use in a LSA framework. As expected, breeding adult survival had the greatest relative effect on population growth, though productivity explained the most variation in growth. Based on perturbation analyses, we demonstrate that even minor reductions in breeding adult survival (<4.5%) caused otherwise stable populations to decline. Despite its importance, precise estimates of spatial and temporal variation in breeding adult survival are poorly documented. Importantly, we found that the ability for increases in reproductive output to compensate for decreased survival was very limited. To maintain stable populations, declines in survival >4% required increases in productivity that generally exceed the evolutionary potential for Golden Eagles. Our findings support the current U.S. Fish and Wildlife conservation strategy which mitigates eagle “take” via efforts to reduce mortality elsewhere.

Journal of Raptor Research↗
USGS2017

Satellite-tagged osprey nearly sets longevity record and productivity response to initial captures

We equipped adult Ospreys ( Pandion haliaetus ) from 24 nests in Oregon/Washington with satellite-tracked battery-powered radios, known as platform transmitter terminals (PTTs), in 1996–1999. These Ospreys from the lower Columbia River (river miles 76–286), and the Willamette Valley in western Oregon were part of a larger study of Osprey fall migration, wintering ecology, and spring migration, which included additional adults from the Upper Midwest and East Coast of the United States ( Martell et al. 2001 , 2014 , Washburn et al. 2014 ). These early-generation PTTs weighed 30–35 g (Microwave Telemetry Inc., Columbia, MD U.S.A.) and utilized the ARGOS tracking system ( www.argos-system.org ). We placed PTTs on the birds' backs using Teflon ribbon (Bally Ribbon, Bally, PA U.S.A.) in a standard backpack configuration ( Kenward 2001 ). With the mass of adult male Ospreys 1400 to 1500 g ( Poole et al. 2002 ), the ratio of tag mass to body mass was 2.0 to 2.5%. Ospreys also received a standard size 8 bird band (U.S. Geological Survey) on one leg and a numbered color band on the other. For more details on trapping techniques, attachment procedures, the battery-powered units, turn-on, turn-off cycles, and tracking equipment, see Martell et al. (2001) .

Oregon, Washington↗
USGS2017

Patterns of spatial distribution of golden eagles across North America: How do they fit into existing landscape-scale mapping systems?

Conserving wide-ranging animals requires knowledge about their year-round movements and resource use. Golden Eagles ( Aquila chrysaetos ) exhibit a wide range of movement patterns across North America. We combined tracking data from 571 Golden Eagles from multiple independent satellite-telemetry projects from North America to provide a comprehensive look at the magnitude and extent of these movements on a continental scale. We compared patterns of use relative to four alternative administrative and ecological mapping systems, namely Bird Conservation Regions (BCRs), U.S. administrative migratory bird flyways, Migratory Bird Joint Ventures, and Landscape Conservation Cooperatives. Our analyses suggested that eagles initially captured in eastern North America used space differently than those captured in western North America. Other groups of eagles that exhibited distinct patterns in space use included long-distance migrants from northern latitudes, and southwestern and Californian desert residents. There were also several groupings of eagles in the Intermountain West. Using this collaborative approach, we have identified large-scale movement patterns that may not have been possible with individual studies. These results will support landscape-scale conservation measures for Golden Eagles across North America.

Journal of Raptor Research↗
USGS2017

Spatial demographic models to inform conservation planning of golden eagles in renewable energy landscapes

Spatial demographic models can help guide monitoring and management activities targeting at-risk species, even in cases where baseline data are lacking. Here, we provide an example of how site-specific changes in land use and anthropogenic stressors can be incorporated into a spatial demographic model to investigate effects on population dynamics of Golden Eagles ( Aquila chrysaetos ). Our study focused on a population of Golden Eagles exposed to risks associated with rapid increases in renewable energy development in southern California, U.S.A. We developed a spatially explicit, individual-based simulation model that integrated empirical data on demography of Golden Eagles with spatial data on the arrangement of nesting habitats, prey resources, and planned renewable energy development sites. Our model permitted simulated eagles of different stage-classes to disperse, establish home ranges, acquire prey resources, prospect for breeding sites, and reproduce. The distribution of nesting habitats, prey resources, and threats within each individual's home range influenced movement, reproduction, and survival. We used our model to explore potential effects of alternative disturbance scenarios, and proposed conservation strategies, on the future distribution and abundance of Golden Eagles in the study region. Results from our simulations suggest that probable increases in mortality associated with renewable energy infrastructure (e.g., collisions with wind turbines and vehicles, electrocution on power poles) could have negative consequences for population trajectories, but that site-specific conservation actions could reduce the magnitude of negative effects. Our study demonstrates the use of a flexible and expandable modeling framework to incorporate spatially dependent processes when determining relative effects of proposed management options to Golden Eagles and their habitats.

California↗
USGS2019

Effects of nest exposure and spring temperatures on golden eagle brood survival: An opportunity for mitigation

We examined Golden Eagle ( Aquila chrysaetos ) brood survival in relation to spring temperatures and exposure of nests to afternoon sun in southwestern Idaho from 1970 through 2012. Most (77%) nests classified as shaded in a subset of 96 nests had northwest to east aspects, and most (71%) nests classified as exposed had south to west aspects. We analyzed survival of 1154 Golden Eagle broods in 64 territories. Golden Eagle brood survival at shaded and exposed nests did not differ when the daily maximum temperature was <32.2°C. Survival in exposed nests declined as the number of days with maximum temperature ≥32.2°C increased, but survival in shaded nests did not change. All broods survived from hatching to fledging age in eight exposed nests with artificial shade structures installed over a 6-yr period. During the same period, 7 of 42 broods in nests without shade structures failed to reach fledging age, with two failures (29%) attributed to thermal stress. Use of artificial shade structures in exposed nests may reduce or prevent mortality caused by heat stress, and thus might be a potential tool for mitigation of “take” from anthropogenic structures and activities. Additional experimentation under an adaptive management framework could provide more information about the effectiveness of using shade structures to offset nestling mortality associated with increasing temperatures predicted by climate change models.

Idaho↗
USGS2019

Non-anthropogenic diet-based oiling of predatory birds

Oiling of wildlife can have important consequences to individual animals and populations (Kingston 2002). Individual birds that are heavily oiled lose their ability to fly and may become ill or die from hypothermia, starvation, exhaustion, or drowning (Clark 1984, Rocke 1999). For example, large-scale oiling from the Exxon Valdez spill caused local declines in populations of many avian taxa (Irons et al. 2000). Although most oiling reports involve marine wildlife exposed to oil leaked from vessels or oil rigs, oiling also can occur in terrestrial environments, for example, via birds drinking water in puddles on asphalt roadways (Clark and Gorney 1987) or landing in oil field wastewater disposal facilities (Trail 2006, Ramírez 2010).

Journal of Raptor Research↗
USGS2019

Genetic variation among island and continental populations of Burrowing Owl (Athene cunicularia) subspecies in North America

Burrowing Owls ( Athene cunicularia ) have a large geographic range spanning both North and South America and resident populations occur on many islands in the eastern Pacific Ocean and the Caribbean Sea. Many owl populations are isolated and disjunct from other populations, but studies on genetic variation within and among populations are limited. We characterized DNA microsatellite variation in populations varying in size and geographic isolation in the Florida ( A. c. floridana ), the Western ( A. c. hypugaea ), and the Clarion ( A. c. rostrata ) subspecies of the Burrowing Owl. We also characterized genetic variation in a geographically isolated population of the western subspecies in central Mexico (near Texcoco Lake). Clarion Burrowing Owls had no intrapopulation variation (i.e., fixation) at 5 out of 11 microsatellite loci, a likely outcome of genetic drift in an isolated and small population. The Florida subspecies had only polymorphic loci but had reduced levels of genetic variation compared with the more-widespread western subspecies that occurs throughout western North America. Despite the extensive geographic distribution of the Western Burrowing Owl, we found genetic differentiation between the panmictic population north of the Trans-Mexican Volcanic Belt and the resident Texcoco Lake population in central Mexico.

Journal of Raptor Research↗
USGS2019

An improved mechanical owl for efficient capture of nesting raptors

Scientific study of raptors often requires the use of a lure to capture individuals for marking or collecting various data and samples. Live lure owls in the genus Bubo are commonly used with mist nets or dho-gazas to trap nesting raptors, but the use of these live lures presents ethical, logistical, and financial challenges. Although owls mounted by taxidermists and mechanical owls have been used in place of a live bird, the success of these types of lures varies widely. We created a more realistic mechanical owl with a greater range of motion than previous models, and then tested the owl on six raptor species in a variety of habitats. For all but one species, capture rates using our mechanical owl were similar to or slightly higher than those reported in studies using live lure owls or previously designed mechanical owls. Time to capture of Northern Goshawks ( Accipiter gentilis ) was, on average, 8 min faster when using our mechanical owl compared to a live owl. Cost analysis revealed that both the initial expense and long-term maintenance of a mechanical owl were less than that of a live lure owl. Mechanical owls can be a useful tool for capturing raptors. Although there are some drawbacks to using a mechanical owl, our results suggest that mechanical birds are comparable to live lure owls and we believe the benefits of using a mechanical owl often outweigh the costs.

Journal of Raptor Research↗
USGS2021

Seasonal and age-related variation in daily travel distances of California Condors

Despite a dramatic recovery from the brink of extinction, California Condors ( Gymnogyps californianus ) still face significant anthropogenic threats. Although condor movement patterns across large temporal scales are understood, less is known about their movements on a fine temporal scale. We used a trajectory-based analysis of GPS telemetry data gathered from condors during 2013 to 2018 to investigate the relationship between the distances condors travel in a day, demographic characteristics (e.g., age and sex), and time of year. Most (>71.4%) daily travel distances by condors were <100 km, and, on average, condors traveled 70.1 ± 60.9 km/d ( x̄ ± SD). On two occasions one condor traveled >400 km in a single day (477 km one day and 415 km the following day). The tendency for condors to travel long distances increased with age, and condors traveled longer distances during the summer and when nesting. Traveling such long distances likely exposes birds to threats across a greater variety of landscapes than would be expected for birds that moved shorter distances. Given anticipated condor range expansion and population increase, this work highlights the importance of coordinating condor conservation across the broad spatial scales at which they move.

California↗
USGS2021

Food habits of American Kestrels in the Southern High Plains of Texas

The American Kestrel ( Falco sparverius ) is in general decline across its North American distribution. In contrast to widespread patterns of decline, kestrel populations appear stable in the southern Great Plains region. Historically, this region had a very low occurrence of kestrels, and their current abundance is highly likely due to vegetation and structures associated with settlement by people of European descent. To determine prey use by breeding kestrels, we placed motion-activated video cameras at preexisting kestrel nest boxes located in the Southern High Plains in 2017. We recorded over 4200 prey deliveries during 1748 hr of observation at five nests over the 4-wk brood-rearing period. On basis of frequency, these deliveries were dominated by reptiles (74.8%), with invertebrates (18.2%), mammals (4.4%), birds (2.9%), and unidentified (1.2%) prey used to lesser extents. Prey delivery rates were high relative to other studies; across the brood-rearing period we recorded an average of 2.3 deliveries/hr, equating to an average of 0.49 deliveries and 3.85 g of prey/nestling/hr. Because invertebrates dominate the diet reported in most kestrel food habit studies, the volume of reptiles captured as prey was unexpected. Even more unanticipated was the number of large prey captured, including juvenile eastern cottontails ( Sylvilagus floridanus ) and ground squirrels ( Ictidomys tridecemlineatus , Xerospermophilus spilosoma ). We suspect the proportion of vertebrate prey captured during the nesting season may explain the local high rates of nesting success and number of young fledged.

Texas↗