We used satellite telemetry during 2011–2015 to identify and characterize wintering areas and migration patterns of Swainson's Hawks (Buteo swainsoni) that bred in California's Central Valley. Twenty tracked hawks wintered across 7500 km from western Mexico to central South America. Wintering areas in Mexico, Central America, and central South America were dominated by agriculture and in northern South America by shrub-scrub. All hawks followed similar migration routes, through the interior of California, Sonoran Desert, and western Mexico, with some continuing through Central America to South America. Compared to northerly wintering birds, birds wintering farther south spent more time in migration, flew greater distance per day during southward (but not northward) migration, spent less time in wintering areas, and arrived later at the breeding area. Central Valley birds substantially used stopover areas (x̄ = 53 d/ individual) during southward migration but returned more directly from wintering to breeding areas (x̄=0.3 stopover d/individual). Most stopovers occurred in western Mexico and the San Joaquin Valley, California. Land cover in stopover areas was dominated by agriculture and shrub-scrub. Use of varied wintering areas that have been altered from native habitat may indicate that migratory and wintering patterns have changed for this population. Advantages of using northern wintering areas may include less time spent in migration and earlier arrival in breeding areas. The diversity of wintering areas may provide resilience from effects of human activities compared to collective wintering in one area. Central Valley Swainson's Hawks’ migration routes and wintering areas differ markedly from those of the rest of the species’ North American population.

The California Fish and Game Commission listed the Swainson's Hawk (Buteo swainsoni) as a state threatened species in 1983 in response to population reductions and habitat loss across the state. Human population increases, urbanization, and shifts in agricultural land use have the potential to affect California's Swainson's Hawk population. In 2005 and 2006, we conducted surveys to estimate the abundance and density of Swainson's Hawk breeding pairs in California's Great (Central) Valley, using a random sampling design stratified across dense, medium, and sparse nesting density strata. The sampling units comprised 2.59-km² (1-mile²) US Public Land Survey System Sections, and the 2-yr survey covered an aggregate total of 682 sampling units (268 in 2005, 414 in 2006). Separate surveyors conducted independent surveys of 29 sampling units in 2006; based on these data, the estimated probability of detecting a single pair (if present) following the multiple-visits protocol was 0.81 (95% CI: 0.58–0.93). After applying this detection-probability correction and using generalized linear modeling of habitat associations to extrapolate density estimates throughout the study area, we estimated that the Great Valley supported 3218 (95% CI: 2271–4165) breeding pairs of Swainson's Hawks in 2005–2006. Our modeling of habitat associations showed crop diversity, alfalfa, and native vegetation as positively associated with the density of Swainson's Hawk breeding pairs, and orchards/vineyards negatively associated. Counts of breeding pairs were also highest in the middle latitudes of the Great Valley, which spans approximately 660 km from north to south. The predictive density model results had some areas of disagreement with the density strata used as basis for the stratified sampling design. To monitor the population status of this species throughout California, we recommend that our 2-yr sampling approach be expanded throughout the state and repeated every 5–10 yr. We also suggest this approach be used to monitor other special status raptor species to track population trend and distributional changes over time.

From 1999 to 2014 we used satellite telemetry to address knowledge gaps in the migration of juvenile Ferruginous Hawks (Buteo regalis) related to their migration independence from adults, migration patterns, and locations of settlement ranges. Nine fledgling hawks migrated independently from their radio-tagged parents, left natal areas at different times and directions, and settled on summer ranges separated from parents by an average of 592 km. Juvenile hawks that we followed through their entire first year (n = 12) travelled about three times farther and twice as long as adults during annual migrations, and arrived an average of 11 to 38 d later on summer, winter, and spring ranges. Hawks that hatched west of the Continental Divide (n = 14) migrated northeast in summer to ranges in the northern grasslands and to winter ranges in California and the Great Plains. Hawks that hatched east of the divide (n = 17) also migrated north to summer ranges, but wintered south from the Central Plains to Mexico. At the end of their first year, hawks (n = 14) settled on spring ranges within their natal regions, an average of 350 km from their hatch locations. In their third spring, hawks (n = 6) settled an average of 123 km from hatch locations and two females nested. We ascribe differences in migration distance and timing of juvenile hawks relative to adults to juveniles’ inexperience in locating suitable feeding areas and range prospecting independently from parents. Because migration patterns and regional fidelity of juvenile Ferruginous Hawks to settlement ranges were similar to those exhibited by adult hawks, the protection of fossorial prey and their habitats on seasonal ranges that promote survival of adult hawks will afford the same benefits to the juvenile cohorts.

We used banding data to investigate dispersal and survival of Red-shouldered Hawks (Buteo lineatus) in two study areas in southern Ohio from 1996 to 2018. Of the 2448 nestlings we banded, 167 (6.8%) were encountered (dead or alive) some time after banding. Mean distance from the natal nest at the time of encounter was 31.6 ± 6.2 km (median = 10.0, range = 0.1–568.6 km, n = 163); natal dispersal distance averaged 16.0 ± 1.9 km (median = 9.0, range = 1.4–117.1 km, n = 110), and was significantly greater for females than for males. Most hawks dispersed <30 km, but 11 hawks (6.7%) dispersed >100 km from their natal nest. Of these long-distance dispersers, nine (82%) were <2 yr old, suggesting that some young birds wander widely prior to breeding. Dispersal distance differed by sex and age at encounter, with dispersal distance negatively correlated with age at encounter, and females dispersing farther (39.8 ± 12.3 km) than males (22.8 ± 9.86 km) and unknown-sex birds (33.9 ± 10.6 km; all P < 0.05; means estimated from the logistical regression model). Dispersal direction for all birds followed a uniform distribution (P > 0.05); however, dispersal direction of long-distance dispersers was not uniform (P < 0.05) but bimodal, with hawks encountered either to the south or to the northeast of the study area. Mean age at recovery was 2.6 ± 0.3 yr (median = 1.5 yr, range = 0.2–10.3 yr). As in other raptor species, apparent annual survival varied between age classes, with young birds (hatch-year and second-year) having lower apparent annual survival (0.49 ± 0.03) than adult birds (0.76 ± 0.03). Our study provides information on dispersal, survival, and causes of mortality of Red-shouldered Hawks, demographic data that are important for evaluating population trends and the sustainability of urban/suburban populations.

Broad-winged Hawks (Buteo platypterus) concentrate in large numbers during migration but several sources suggest regional declines in eastern North America may be occurring, perhaps due to increasing human development, natural resource exploitation, and suburbanization of forests. To better understand the natural history of this secretive nesting species, we used both direct field observations and video cameras to study the nesting ecology of Broad-winged Hawks in three geographic regions of Pennsylvania, each with varying degrees of forest fragmentation. We recorded adult nest attendance, prey deliveries, and nest material deliveries from incubation through fledging. During 891 hr of observation during the nestling period, adult hawks were absent from the nest >72% of the time. Of the time at least one adult was present at the nest during the nestling stage, 77% was spent standing and sheltering, 21% feeding young, and 1% consuming food. Both adults were present at the nest <1% of the time. Mammals, birds, and reptiles and amphibians were the most frequently delivered prey items in that order, with the eastern chipmunk (Tamias striatus) composing >16% of the total prey delivered. Prey deliveries were more frequent during the first 3 wk of the nestling period than during the last 2 wk of the nestling period, but did not vary by time of day. The most frequently delivered nesting material was deciduous sprigs, which made up 55% of deliveries. Nest materials were delivered from incubation until the young were 4 wk old, but delivery rates varied significantly by nesting stage and nestling age. The absence of adults at the nests during nestling and fledgling periods may leave young vulnerable to predators. Although our sample size of nests in fragmented forests was too small for statistical analysis, the relationship between forest fragmentation and Broad-winged Hawk nesting ecology warrants further investigation.

Red-tailed Hawks (Buteo jamaicensis) are common across North America and are well-adapted to human-altered landscapes. Yellowstone National Park offers an opportunity to study this nearly ubiquitous species in a relatively unaltered and intact temperate ecosystem. In anticipation of future habitat and environmental change, we monitored Red-tailed Hawk territories and nests across the park's northern range to establish a baseline of hawk density, reproduction, and population status. We used a combination of intensive territory monitoring at two different scales and roadside point count surveys, analyzed using detection-dependent density modeling. From 2011 through 2015, we monitored between 17 and 44 territories each year and, in total, documented at least 60 territories in the northern range. Territory density across the northern range was comparable with other regional estimates, but local density was particularly high on the Blacktail Deer Plateau. On average, 87% of territorial pairs (range: 75–100%) laid eggs and breeding success averaged 63% (range: 48–89%). Hawk reproductive rate averaged 1.07 (range: 0.46–1.74) young per occupied territory and brood size averaged 1.73 (range: 1.30–1.96) young per successful nest. Reproductive rate varied significantly between study years but on average was well below the level thought necessary for a stable population, underscoring the importance of continued monitoring to better understand the drivers of population trends.

We report late Quaternary fossils of the hind limb (tibiotarsus, tarsometatarsus, hallux, pedal phalanges) of an extinct species of eagle (Accipitridae) from Hispaniola (Haiti, Dominican Republic). We are unable to refer these 24 fossils with confidence to any Accipitrid genus, living or extinct. Among living genera, the Hispaniolan fossils are most similar in nonquantitative characters to leg elements in Geranoaetus Kaup 1844, as represented in our comparisons by the South American species Black-chested Buzzard-Eagle (G. melanoleucus Vieillot 1819). Although it may be that Geranoaetus eventually will be found to accommodate the Hispaniolan eagle and perhaps other large, extinct species of West Indian eagles (from Cuba and Bahamas), the fossil material available at this time is inadequate. Generic assignment is complicated further by uncertain generic limits among surviving New World buteonine/buteogalline hawks and eagles, which themselves also are not well represented in scientific collections. Measures of the tibiotarsus suggest the Hispaniolan eagle was 15–30% larger than the extant Golden Eagle (Aquila chrysaetos). It is likely that the large Hispaniolan eagle went extinct along with, and potentially as a consequence of, the extinction of most endemic species of large- and medium-sized mammals (primates, rodents, and sloths) that once served as prey.

American Kestrels (Falco sparverius) are North America's most abundant falcon, but they are declining throughout much of their range. Studies of nesting success are common, but far less is known about kestrels during migration and on the wintering grounds. We studied kestrels wintering along county roadways in South Texas. We trapped and color-marked 65 kestrels during October through December in 2014 and 2015 and searched for marked individuals once per week using a spotting scope, until birds started departing from the wintering grounds. We also searched for returning kestrels from September to March, 2015–2016 and 2016–2017. We used the Cormack–Jolly–Seber (CJS) models in Program MARK to estimate apparent survival, and we estimated two metrics of site fidelity as well as a spatial metric of site fidelity. We estimated territory size for individuals with ≥10 locations using the maximum linear distance between locations. We estimated winter survival (20 wk) as 67.1 ± 7.1% for kestrels in the winter they were marked and 84.4 ± 6.3% for returning birds. The 2-yr average apparent winter site fidelity was 27.8% for males and 50.2% for females, and the 2-yr average adjusted winter site fidelity was 41.7% for males and 65.7% for females. Linear average territory size ranged from 539 ± 34 m in Winter 3 to 738 ± 74 m in Winter 1. Our estimates of site fidelity are 12–15% greater than previously reported, and our linear winter territory sizes (pooled over 3 yr) were less than half the size of those previously reported for wintering American Kestrels. Small territories and high winter site fidelity suggest that South Texas agricultural areas are likely an important region for wintering kestrels.