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At least 73 records · Page 4Linked to original sources
USGS2008

Use of body mass, footpad length, and wing chord to determine sex in Swainson's Hawks

Many studies of avian ecology require an expedient means to determine sex, and the use of molecular techniques has provided an effective and accurate means to determine sex of raptors in the field ( Sarasola and Negro 2004 , Donohue and Dufty 2006 ). Sometimes investigators need to rely on morphometric measurements to determine sex of monochromatic species such as Swainson's Hawks ( Buteo swainsoni ) because they lack funds or facilities to use molecular techniques or they are analyzing extant data. Discriminant analyses conducted on morphometric measurements have been effective for sexing many raptor species (e.g., Edwards and Kochert 1986 , Bavoux et al. 2006 , Donohue and Dufty 2006 ). Sarasola and Negro (2004) recently reported on the effectiveness of seven morphometric measurements as means to identify sex of Swainson's Hawks on the hawk's austral summer areas in Argentina. They proposed a combination of the length of forearm, wing chord, and tail as an effective means to determine sex, with an overall accuracy of 93%. However, Sarasola and Negro (2004) did not assess the effectiveness of using footpad length (sometimes called toe-pad) to classify sex of these hawks. Footpad length and mass were quite effective in sexing Golden Eagles ( Aquila chrysaetos ), a species with a degree of dimorphism similar to that of Swainson's Hawks ( Snyder and Wiley 1976 ), with an overall accuracy of 98% ( Edwards and Kochert 1986 ). We here report the utility of using footpad length and mass, as well as wing chord length, as a means of sexing Swainson's Hawks on the nesting grounds.

Idaho↗
USGS2008

Region-wide trends of nesting ospreys in northwestern Mexico: a three-decade perspective

We used a double-sampling technique (air plus ground survey) in 2006, with partial double coverage, to estimate the present size of the Osprey (Pandion haliaetus) nesting population in northwestern Mexico (coastal Baja California, islands in the Gulf of California, and coastal Sonora and Sinaloa). With the exception of Natividad, Cedros, and San Benitos islands along the Pacific coast of Baja California (all three excluded from our coverage in 2006 due to fog), this survey was a repeat of previous surveys conducted by us with the same protocol in 1977 and 1992/1993, allowing for estimates of regional population trends. The minimum population estimate for the area we surveyed in 2006 was 1343 nesting pairs, an 81% increase since 1977, but only a 3% increase since 1992/1993. The population on the Gulf side of Baja California generally remained stable during the three surveys (255, 236, and 252 pairs, respectively). The population of the Midriff Islands (Gulf of California in the vicinity of 29°N latitude) remained similar from 1992/1993 (308 pairs) to 2006 (289 pairs), but with notable population changes on the largest two islands (Guardian Angel: 45 to 105 pairs [133% increase]; Tiburón: 164 to 109 pairs [34% decrease]). The minimum estimated Osprey population on the Sonora mainland decreased in a manner similar to adjacent Isla Tiburón, i.e., by 26%, from 214 pairs in 1993 to 158 pairs in 2006. In contrast, the population in coastal Sinaloa, which had increased by 150% between 1977 and 1993, grew again by 58% between 1993 and 2006, from 180 to 285 pairs. Our survey confirmed previously described patterns of rapid population changes at a local level, coupled with apparent shifts in spatial distribution. The large ground-nesting population that until recently nested on two islands in San Ignacio Lagoon ( Pacific Ocean side, Baja California) was no longer present on the islands in 2006, but an equivalent number of pairs were found to the north and south of the lagoon, nesting in small towns and along adjoining overhead electric lines, with no overall change in population size for that general area (198 pairs in 1992; 199 in 2006). Use of artificial nesting structures was 4.3% in 1977 and 6.2% in 1992/1993, but jumped to 26.4% in 2006. Use of poles that support overhead electric lines poses a risk of electrocution to Ospreys and also causes power outages and fires. We recommend modification of these poles to safely accommodate Osprey nests, as has been successfully accomplished in many countries.

Journal of Raptor Research↗
USGS2009

Movements of juvenile Gyrfalcons from western and interior Alaska following departure from their natal areas

J uvenile raptors often travel thousands of kilometers from the time they leave their natal areas to the time they enter a breeding population. Documenting movements and identifying areas used by raptors before they enter a breeding population is important for understanding the factors that influence their survival. In North America, juvenile Gyrfalcons ( Falco rusticolus ) are routinely observed outside the species' breeding range during the nonbreeding season, but the natal origins of these birds are rarely known. We used satellite telemetry to track the movements of juvenile Gyrfalcons during their first months of independence. We instrumented nestlings with lightweight satellite transmitters within 10 d of estimated fledging dates on the Seward Peninsula in western Alaska and in Denali National Park (Denali) in interior Alaska. Gyrfalcons spent an average of 41.4 ± 6.1 d (range = 30–50 d) in their natal areas after fledging. The mean departure date from natal areas was 27 August ± 6.4 d. We tracked 15 individuals for an average of 70.5 ± 28.1 d post-departure; Gyrfalcons moved from 105 to 4299 km during this period and tended to move greater distances earlier in the tracking period than later in the tracking period. Gyrfalcons did not establish temporary winter ranges within the tracking period. We identified several movement patterns among Gyrfalcons, including unidirectional long-distance movements, multidirectional long- and short-distance movements, and shorter movements within a local region. Gyrfalcons from the Seward Peninsula remained in western Alaska or flew to eastern Russia with no movements into interior Alaska. In contrast, Gyrfalcons from Denali remained in interior Alaska, flew to northern and western Alaska, or flew to northern Alberta. Gyrfalcons from both study areas tended to move to coastal, riparian, and wetland areas during autumn and early winter. Because juvenile Gyrfalcons dispersed over a large geographic area and across three international boundaries, conservation efforts should focus on both regional and international scales.

Journal of Raptor Research↗
USGS2009

Recovery distances of nestling Bald Eagles banded in Florida and implications for natal dispersal and philopatry

I used band recovery data to examine distances between banding and recovery locations for 154 nestling Florida Bald Eagles and discuss the implications for understanding natal dispersal and philopatry in this species. Band recoveries occurred in 23 U.S. states and five Canadian provinces between 1931&ndash;2005. Recovery distance from the natal nest averaged longer for the youngest age classes (ANOVA: F = 3.59; df = 5, 153; P = 0.005), for individuals banded in earlier decades ( F = 1.94; df = 5, 153; P = 0.093), and for the months of May through October ( F = 3.10; df = 12, 153; P < 0.001). Of 35 individuals classed as mature (&ge;3.9 yr old when recovered; range 3.9&ndash;36.5 yr), 31 were located within Florida, which suggested a strong degree of philopatry to the natal state. Among 21 mature eagles of known sex with known banding and recovery locations in Florida, females, particularly younger birds, had longer recovery distances ( N = 9, mean = 93 km, SE = 22.4) than did males ( N = 12, mean = 31 km, SE = 5.3; t = 2.67, df = 19, P = 0.026). The records examined here suggest a high degree of philopatry and relatively short natal dispersal distances, particularly in male Bald Eagles.

Journal of Raptor Research↗
USGS2010

Repeated use of an abandoned vehicle by nesting Turkey vultures ( Cathartes aura )

Turkey Vultures ( Cathartes aura ) lay their eggs on an existing substrate in the dark recesses of a variety of natural sites ( Kirk and Mossman 1998 ). Although an important requirement of Turkey Vulture nest-site selection is isolation from human disturbances ( Kirk and Mossman 1998 ), their nests have been reported in abandoned buildings since at least the early 1800s ( Nuttall 1832 ). Depopulation of rural areas in North America in recent decades has resulted in many abandoned buildings within the Turkey Vulture's breeding range ( Peck 2003 ). Increased use of abandoned buildings by nesting Turkey Vultures has been implicated in the species' recent northward range expansion ( Peck 2003 , Nelson et al. 2005 , Houston et al. 2007 ). Although abandoned or inoperative vehicles also are widespread in rural areas, we found no published literature documenting Turkey Vultures' use of these potential nest sites. Herein, we summarize the first documented incidence of a Turkey Vulture nesting in an abandoned vehicle.

South Dakota↗
USGS2010

Detection probability of cliff-nesting raptors during helicopter and fixed-wing aircraft surveys in western Alaska

We conducted repeated aerial surveys for breeding cliff-nesting raptors on the Yukon Delta National Wildlife Refuge (YDNWR) in western Alaska to estimate detection probabilities of Gyrfalcons (Falco rusticolus), Golden Eagles (Aquila chrysaetos), Rough-legged Hawks (Buteo lagopus), and also Common Ravens (Corvus corax). Using the program PRESENCE, we modeled detection histories of each species based on single species occupancy modeling. We used different observers during four helicopter replicate surveys in the Kilbuck Mountains and five fixed-wing replicate surveys in the Ingakslugwat Hills near Bethel, AK. During helicopter surveys, Gyrfalcons had the highest detection probability estimate (p^;p^ 0.79; SE 0.05), followed by Golden Eagles (p^=0.68; SE 0.05), Common Ravens (p^=0.45; SE 0.17), and Rough-legged Hawks (p^=0.10; SE 0.11). Detection probabilities from fixed-wing aircraft in the Ingakslugwat Hills were similar to those from the helicopter in the Kilbuck Mountains for Gyrfalcons and Golden Eagles, but were higher for Common Ravens (p^=0.85; SE 0.06) and Rough-legged Hawks (p^=0.42; SE 0.07). Fixed-wing aircraft provided detection probability estimates and SEs in the Ingakslugwat Hills similar to or better than those from helicopter surveys in the Kilbucks and should be considered for future cliff-nesting raptor surveys where safe, low-altitude flight is possible. Overall, detection probability varied by observer experience and in some cases, by study area/aircraft type.

Alaska↗
USGS2010

Bald eagle predation on common loon egg

The Common Loon ( Gavia immer ) must defend against many potential egg predators during incubation, including corvids, Herring Gulls ( Larus argentatus ), raccoons ( Procyon lotor ), striped skunk ( Mephitis mephitis ), fisher ( Martes pennanti ), and mink ( Neovison vison ) ( McIntyre 1988 , Evers 2004 , McCann et al. 2005 ). Bald Eagles ( Haliaeetus leucocephalus ) have been documented as predators of both adult Common Loons and their chicks ( Vliestra and Paruk 1997 , Paruk et al. 1999 , Erlandson et al. 2007 , Piper et al. 2008 ). In Wisconsin, where nesting Bald Eagles are abundant (>1200 nesting pairs, >1 young/pair/year), field biologists observed four instances of eagle predation of eggs in loon nests during the period 2002&ndash;2004 (M. Meyer pers. comm.). In addition, four cases of eagle predation of incubating adult loons were inferred from evidence found at the loon nest (dozens of plucked adult loon feathers, no carcass remains) and/or loon leg, neck, and skull bones beneath two active eagle nests, including leg bones containing the bands of the nearby (<25 m) incubating adult loon. However, although loon egg predation has been associated with Bald Eagles, predation events have yet to be described in peer-reviewed literature. Here we describe a photographic observation of predation on a Common Loon egg by an immature Bald Eagle as captured by a nest surveillance video camera on Lake Umbagog, a large lake (32 km 2 ) at Umbagog National Wildlife Refuge (UNWR) in Maine.

Maine↗
USGS2011

The winter diet of short-eared owls in subtropical Texas: Do southern diets provide evidence of opportunity?

Winter diet of the Short-eared Owl ( Asio flammeus ) in Texas is little known. We investigated the diet of Short-eared Owls wintering in McMullen County, in subtropical Texas, by analyzing the contents of 129 pellets collected over two winters (28 November 2007 to 22 February 2008 and 11 December 2008 to 11 February 2009) and conducted a latitudinal-based comparison of published diet studies of Short-eared Owls. In southern Texas, we recovered the remains of 162 prey items, 98% of which were vertebrates. Hispid cotton rats ( Sigmodon hispidus ) were the most important prey species in terms of percent of total number (67%) and percent of total biomass (87%). Most (86%) Short-eared Owl diet studies (based on &ge;100 pellets) have been conducted north of 35&deg;N, with only six studies, including the present study, conducted at or south of 35&deg;N latitude. Voles (primarily Microtus spp.) were the dominant prey in North American studies (71%), but microtines were not the dominant prey in any of the six studies conducted south of 35&deg;N latitude. We suggest that Short-eared Owls do not specialize on microtines, as is often implied, but rather depend on rodents with cyclic populations, such as the hispid cotton rat in southern areas.

Texas↗
USGS2011

Northern goshawk monitoring in the western Great Lakes bioregion

Uncertainties about factors affecting Northern Goshawk ( Accipiter gentilis ) ecology and the status of populations have added to the challenge of managing this species. To address data needs for determining the status of goshawk populations, Hargis and Woodbridge (2006) developed a bioregional monitoring protocol based on estimating occupancy. The goal of our study was to implement this protocol and collect data to determine goshawk population status in the western Great Lakes (WGL) bioregion, which encompasses portions of Minnesota, Wisconsin, and Michigan, and is a mixture of private and public property. We used 366 goshawk nest locations obtained between 1979 and 2006 throughout the WGL bioregion to develop a model of landscape use consisting of forest canopy cover and land-cover covariates. We then used the model to develop a stratified sampling design for selecting 600-ha Primary Sampling Units (PSUs) to survey for goshawks. Project collaborators surveyed 86 PSUs for goshawk presence using broadcasted calls twice between mid-May and mid-August 2008, and recorded 30 goshawk detections in 21 different PSUs. Seventy-four percent of detections occurred at call stations with canopy closure >75%. Goshawk detection probabilities were 0.549 ± 0.118 (standard error) for the first visit to PSUs and 0.750 ± 0.126 for the second visit. We estimated the proportion of PSUs occupied by goshawks as 0.266 ± 0.047, which corresponded to 5184 ± 914 PSUs occupied by goshawks in our study area and suggested that goshawks are widely, but sparsely, distributed throughout the WGL bioregion.

Michigan, Minnesota, Wisconsin↗
USGS2011

Collection of mammal manure and other Debris by nesting Burrowing Owls

Burrowing Owls ( Athene cunicularia ) routinely collect and scatter dry manure of mammals around their nesting burrows. Recent studies have suggested this behavior attracts insect prey to the nesting burrow. However, some Burrowing Owls do not use manure, but instead, collect and scatter other materials (e.g., grass, moss, paper, plastic) around their nesting burrow in a similar fashion. Use of these materials seemingly contradicts the prey-attraction hypothesis. Using observational and experimental methods, we tested whether Burrowing Owls preferred manure to other materials commonly found at nesting burrows in eastern Washington. We found a wide variety of materials at nests, but grass and manure were the most common materials. The amount of manure present at nests was negatively correlated with the amount of other materials, and with the distance to the nearest source of manure. Burrowing Owls showed no preference between horse manure and grass divots at experimental supply stations that we placed near nesting burrows. They did prefer these two materials to carpet pieces and aluminum foil (both materials that are often found at Burrowing Owl nests). Our results did not support the premise that Burrowing Owls specifically seek out manure when lining their nesting burrows. The unusual behavior of collecting and scattering mammal manure and other debris at Burrowing Owl nests may serve functions other than (or in addition to) prey attraction and alternative hypotheses need further testing before the function of this behavior is certain.

Journal of Raptor Research↗
USGS2011

Sex-related differences in habitat associations of wintering American Kestrels in California's Central Valley

We used roadside survey data collected from 19 routes over three consecutive winters from 2007–08 to 2009–10 to compare habitat associations of male and female American Kestrels ( Falco sparverius ) in the Central Valley of California to determine if segregation by sex was evident across this region. As a species, American Kestrels showed positive associations with alfalfa and other forage crops like hay and winter wheat, as well as grassland, irrigated pasture, and rice. Habitat associations of females were similar, with female densities in all these habitats except rice significantly higher than average. Male American Kestrels showed a positive association only with grassland and were present at densities well below those of females in alfalfa, other forage crops, and grassland. Males were present in higher densities than females in most habitats with negative associations for the species, such as orchards, urbanized areas, and oak savannah. The ratio of females to males for each route was positively correlated with the overall density of American Kestrels on that route. Our findings that females seem to occupy higher quality habitats in winter are consistent with observations from elsewhere in North America.

California↗
USGS2011

Female American Kestrel survives double amputation

Free-ranging raptors are susceptible to a variety of injuries, many of which are sustained while pursuing and/or capturing live prey. Injuries hindering an individual’s ability to capture prey, such as partial blindness, damage to the bill, and foot or leg injuries, are debilitating and potentially life-threatening. However, there are ample observations in the literature of free-ranging raptors with eye (Bedrosian and St.Pierre 2007), bill (Strobel and Haralson-Strobel 2009) and foot and leg injuries (Blodget et al. 1990, Murza et al. 2000, Dwyer 2006, Bedrosian and St.Pierre 2007), suggesting that some individuals are able to compensate for their injuries if only partial functionality is lost (e.g., loss of only one eye). Reports of injuries resulting in the complete loss of functionality (e.g., loss of both eyes) are rare as individuals suffering such severe trauma presumably do not survive long. Here we report the capture on a bal-chatri trap of an American Kestrel (Falco sparverius; hereafter kestrel) with previous amputation of both legs

Journal of Raptor Research↗
USGS2013

Migration and habitat preferences of Swainson's Hawks at an autumn stopover site in northwestern Texas

Unlike most raptors, the Swainson's Hawk (Buteo swainsoni) migrates long distances between breeding and wintering ranges, which elevates the importance of stopover sites for foraging. We conducted three years of fall surveys in the Southern High Plains of Texas. Migrant Swainson's Hawks moved through the area mostly between July and mid-October, peaking in September. Subadults tended to migrate earlier than adults, and light morphs before dark morphs. Favored foraging habitats included silage corn, green beans, and alfalfa, but the hawks foraged primarily where ongoing agricultural activities disturbed prey and made them more available.

Texas↗
USGS2013

Survival and home-range size of Northern Spotted Owls in southwestern Oregon

In the Klamath province of southwestern Oregon, Northern Spotted Owls (Strix occidentalis caurina) occur in complex, productive forests that historically supported frequent fires of variable severity. However, little is known about the relationships between Spotted Owl survival and home-range size and the characteristics of fire-prone, mixed-conifer forests of the Klamath province. Thus, the objectives of this study were to estimate monthly survival rates and home-range size in relation to habitat characteristics for Northern Spotted Owls in southwestern Oregon. Home-range size and survival of 15 Northern Spotted Owls was monitored using radiotelemetry in the Ashland Ranger District of the Rogue River–Siskiyou National Forest from September 2006 to October 2008. Habitat classes within Spotted Owl home ranges were characterized using a remote-sensed vegetation map of the study area. Estimates of monthly survival ranged from 0.89 to 1.0 and were positively correlated with the number of late-seral habitat patches and the amount of edge, and negatively correlated with the mean nearest neighbor distance between late-seral habitats. Annual home-range size varied from to 189 to 894 ha ( x = 576; SE = 75), with little difference between breeding and nonbreeding home ranges. Breeding-season home-range size increased with the amount of hard edge, and the amount of old and mature forest combined. Core area, annual and nonbreeding season home-range sizes all increased with increased amounts of hard edge, suggesting that increased fragmentation is associated with larger core and home-range sizes. Although no effect of the amount of late-seral stage forest on either survival or home-range size was detected, these results are the first to concurrently demonstrate increased forest fragmentation with decreased survival and increased home-range size of Northern Spotted Owls.

Oregon↗
USGS2012

Frequency of nest use by golden eagles in southwestern Idaho

We studied nest use by Golden Eagles (Aquila chrysaetos) from 1966 to 2011 to assess nest reuse within territories, ascertain the length of time that elapses between uses of nests, and test the hypotheses that reproductive success and adult turnover influence nest switching. Golden Eagles used 454 nests in 66 territories and used individual nests 1 to 26 times during 45 continuous years of observation. Time between reuse ranged from 1 to 39 yr. Distances between nearest adjacent alternative nests within territories ranged between <1 and 1822 m, and distances between 90% of adjacent nests were <500 m. Of all nests used, 21% fell or disintegrated, and 31% were newly constructed during the study. Nest switching was not associated with the previous year's nesting success, but eagles tended to change nests after turnover of at least one member of the pair. Five of 42 nests used in 1971 and monitored continuously through 2011 were used only once and 21 were used >5 times. Two nests were unused for 21 and 27 yr after 1971 before being used every 1 to 3 yr thereafter. Eagles used 43% of the nests in series of consecutive years (range 3 to 20 consecutive nestings). Protecting unused nests for a proposed 10 yr after the last known use would not have protected 34% of all 300 nests that were reused during the study and 49% of 37 reused nests monitored consistently for 41 yr. The 102 nests that would not have received protection were in 56 of the 66 territories.

Idaho↗
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 (&ge;1 young fledged) was 44.4% in 1999 with an average of 1.43 &plusmn; 0.09 (SE) young produced per successful pair. Productivity was similar in 2000, with 58.2% nesting success and 1.83 &plusmn; 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↗