Genetic analysis confirms first record of polygyny in Cooper's Hawks
[No abstract available]
Journal of Raptor Research↗
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Using molecular sexing to assess field-based sexing techniques in the Madagascar Fish-Eagle
[No abstract available]
Journal of Raptor Research↗
Northern Goshawk (Accipiter gentilis) home range, movement and forays revealed by GPS-tracking
The Northern Goshawk ( Accipiter gentilis ) is an apex predator occurring across North America and Eurasia. The species has received considerable conservation focus in late-seral conifer forests of western North America, where its habitat has been substantially reduced and altered by timber harvest and is increasingly at risk from high severity fire, drought, and forest pathogens. In the Sierra Nevada range of California, management and conservation of goshawks are hampered by a lack of knowledge of their basic space use and movement ecology. We used global positioning system (GPS) loggers to investigate space use of 20 resident, adult Northern Goshawks over 3 yr (2015–2018) in the Plumas National Forest, California. Median home range sizes of male goshawks were more than twice as large as those of females, and nonbreeding-season home ranges were three times larger than breeding-season home ranges. High resolution GPS data (location interval 1–6 min) allowed quantification of daily transit distances up to 60 km for individual goshawks and revealed long-distance forays into adjacent territories and surrounding areas. Four goshawks (three males, one female) undertook forays >8 km from their nest locations, with forays lasting up to 6 d; these forays occurred during both breeding and nonbreeding seasons for both sexes. Comparing our results to current conservation approaches, we determined that USDA Forest Service goshawk Protected Activity Centers protected <25% of both the roost locations and the area used during the daytime. Conservation efforts for Northern Goshawks in the Sierra Nevada would benefit from consideration of year-round habitat needs at larger scales than previously thought.
California↗
Long-term population fluctuations of a Burrowing Owl population on Kirtland Air Force Base, New Mexico, USA
Western Burrowing Owls ( Athene cunicularia hypugaea ; hereafter, Burrowing Owls) were once widespread residents of grasslands throughout western North America, but their range has contracted, and abundance has declined in some regions. The causes of declines and geographic variation in population trends of Burrowing Owls are unclear but may be linked to changing land use and urbanization. Burrowing Owls are often found in association with airfields and airports, and their presence at such facilities is sometimes considered to be in conflict with those operations. Documenting the long-term persistence of Burrowing Owls at active airfields can help airfield managers who face decisions regarding compatibility of owls and airfield operations. We report the results of a long-term effort to monitor Burrowing Owls on Kirtland Air Force Base in New Mexico, USA, including the rapid recovery of Burrowing Owl numbers from near-extirpation and the relationships between abundance and other demographic traits. The number of breeding pairs of Burrowing Owls increased from one pair in 2013 to 28 pairs in 2019 and 2020, and the number of fledglings produced increased from one in 2013 to 84 in 2019 and 61 in 2020. The recovery was not uniform across all areas of Kirtland Air Force Base, and some formerly occupied areas remained unoccupied. We documented dispersal outside the Air Force base boundary and that the number of breeding pairs was more strongly influenced by the number of offspring produced in the prior year than the number of owls returning from prior years, which indicated that the population is part of a larger meta-population. Our results demonstrate that the maintenance of Burrowing Owl populations is not necessarily at odds with safe airfield operations, that Burrowing Owls exhibit complex population dynamics, and can rapidly recolonize previously occupied areas if habitat and nest sites remain suitable.
New Mexico↗
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↗
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↗
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 1931–2005. 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 (≥3.9 yr old when recovered; range 3.9–36.5 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↗
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↗
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↗
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 2002–2004 (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↗
Prey use by Swainson's Hawks in the lesser prairie-chicken range of the southern high plains of Texas
[No abstract available]
Journal of Raptor Research↗
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 ≥100 pellets) have been conducted north of 35°N, with only six studies, including the present study, conducted at or south of 35°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°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↗
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↗
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↗
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↗
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↗
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↗