Avian communal roosts provide insight into evolution and serve as focal points for conservation. Nonbreeding Crested Caracaras (Caracara cheriway; hereafter caracaras) use communal roosts, but evolutionary implications have not been explored. Though nonbreeding caracaras are nonmigratory, the scientific literature fails to explain seasonal differences in their movement and survival concurrent with seasonal consistency in their habitat and social ecology. In the Social Refuge–Territory Prospecting hypothesis we propose, socially subordinate nonbreeding caracaras precluded from breeding by habitat limitation use communal roosts as social refuges to avoid aggression from dominant territory holders during nonbreeding seasons, and engage in territory prospecting during breeding seasons. Communal roosts thus become central places from which to forage not for food, but for a breeding territory. Because foraging gains are stored as remembered information, competition costs resulting from public information are preempted. For the Social Refuge–Territory Prospecting hypothesis to be valid, two criteria need to be met. First, communal roost use needs to be higher during nonbreeding seasons. Second, a measure of fitness needs to be used to evaluate the hypothesis as an evolutionarily stable strategy. To meet these criteria, in this study we report that numbers of nonbreeding caracaras using a communal roost in Florida are higher during nonbreeding seasons (mean = 111.8 individuals / night) than during breeding seasons (mean = 60.7 individuals / night) as counted from August 2006–April 2009 (n = 407 counts). We also compare differential survival by season from previous work to demonstrate that by limiting exploratory movements to times when prospecting is most informative, nonbreeding caracaras balance maximizing survival against the likelihood of securing a breeding territory. Our hypothesis provides a unifying explanation for otherwise unexplained paradoxes in the ecology of nonbreeding caracaras, and may be useful in guiding conservation and expanding our understanding of the ecology of other communally roosting birds.

From 2005 to 2009 we evaluated the activity patterns and food habits of White-tailed Kites (Elanus leucurus) during the breeding and nonbreeding seasons in the Argentine Pampas. According to time-activity budget analyses, perching was the most frequently observed activity during the nonbreeding season (52% of total time), whereas foraging was the most frequent activity during the breeding season (41% of total time). Flight was the least frequent of all kites' activities in both seasons (8% and 9% during the breeding and nonbreeding season, respectively). Even when kites spent a similar percentage of time foraging during both breeding and nonbreeding seasons (41% and 39%, respectively), their hunting technique differed between seasons. During the nonbreeding season, we only observed kites using active searching to forage, but during the breeding season, we observed them using active and passive searching in similar proportions. According to pellet analyses, the diet of kites was mostly composed of rodents (> 96% of total prey). Small rodents (body mass < 35 g) were dominant in numeric terms in the diet in both seasons, but larger rodents represented the bulk of biomass. Our results indicate that in the Argentine Pampas, White-tailed Kites are predominantly mammal-eating, active-search predators, as previously reported for the species in South America and North America and for other Elanus species around the world.

A few breeding populations of White-rumped Vultures (Gyps bengalensis) still survive in pockets of their original vast range in India, having weathered a diclofenac-induced population decline of 99.9% since the early 1990s. These breeding populations are potential sources of recruits, now that the overall population appears to be stabilizing or even recovering in some areas. We studied two White-rumped Vulture nesting colonies in the Raigad district of coastal Maharashtra in 2013–2014, to investigate site-specific nesting success and nest-site selection. Our overall aim was to better understand the capability of these remnant populations to contribute to the stability of vulture populations at a landscape scale. We found that vultures preferred to nest in taller trees. Nest failure was high before hatching but declined thereafter. Overall nesting outcome was unrelated to the distance of the nest from areas of disturbance, but may have been influenced by characteristics of nest trees. The percentage of successful nests was higher in the smaller colony, suggesting that colony size may not be the only best criterion for targeting conservation efforts.

Bearded Vulture (Gypaetus barbatus) populations are declining across most of the species' global range. We studied Bearded Vultures in the Annapurna Himalaya Range of Nepal using line-transect distance sampling, and quantified the perceptions of threats to the species by interviewing local people in two different elevational areas. We recorded 35 Bearded Vultures (26 adults, 5 non-adults, 4 birds of unknown age) along a 168-km transect, yielding an encounter rate of 0.21 individuals/km. Based on distance sampling, we estimated a vulture density of 0.184 individuals/km² in the study area. Local people in the two areas perceived population status and threats to the Bearded Vulture differently. At the lower elevational range (1398–2108 m), people perceived that the vulture population is declining and that the major threats are food shortage and secondary poisoning via the use of poisons by livestock herders to kill mammalian carnivores. At higher elevations (2538–3813 m), people perceived that the vulture population is stable with no lack of food; there also was a larger prevalence of the use of vulture body parts for traditional medicine in this area. Our study suggests that unintentional poisoning, food shortage, and use of vulture body parts are the primary threats to the Bearded Vulture in the Annapurna Himalaya Range of Nepal.

Although many Western Burrowing Owl (Athene cunicularia hypugaea) populations have been declining, a high-density population nests at the National Radio Transmission Facility (NRTF), Dixon, California. We compared density at NRTF to densities elsewhere, and nest-site use and reuse to available nest substrates. Breeding pairs numbered 24–44 per year, averaging 34 pairs on 83 ha, the fourth-highest on record. Occupancy of eight artificial nest sites installed in 2000 declined from six pairs in 2006 to one pair in 2007 and 2008, and none afterward. Nearest-neighbor distance among artificial nests averaged half the distance among nest sites in fossorial mammal burrows and concrete half-rounds covering aboveground power cables. Undisturbed clay soils supported pocket gophers (Thomomys bottae) but few ground squirrels (Spermophilus beecheyi), whereas disturbed soils supported both ground squirrels and Burrowing Owls. The presence of both ground squirrels and Burrowing Owls was associated with backfill soils over buried cable, cable covers, and areas where soils bordered impervious surfaces. Nest-site reuse was low, with only 12% of the sites occupied in all study years, 2006–2011. Most (78%) nest sites reused in a subsequent year involved nests in a different burrow or cable cover opening >1 m from the previous year's nest. We recommend research on whether concrete half-rounds might outperform buried utility boxes as artificial nests, especially in conjunction with efforts to conserve the fossorial mammals that naturally excavate burrows used by Burrowing Owls.

Ungulate carrion supports an unusual canine-corvid-eagle winter scavenging guild in northern Arizona. To evaluate the effect of location and habitat on carcass use and longevity, between December 1996 and April 2008 we recorded 870 observations of Bald Eagles (Haliaeetus leucocephalus), Common Ravens (Corvus corax) and coyotes (Canis latrans) scavenging 123 ungulate carcasses: 103 elk (Cervus canadensis), 12 mule deer (Odocoileus hemionus), seven pronghorn antelope (Antilocapra americana), and one domestic cow (Bos taurus). Our temporal metric for measuring carcass longevity and scavenger presence was carcass-day (CD), numbered consecutively from the first day a carcass was recorded until it was consumed. We observed 38 separate carcasses (individual placement), 39 carcasses as part of three-carcass arrays in habitat associated with open, edge, and forest cover types (simultaneous choice), 22 carcasses left along the roadway where killed (monitored in place), and 24 carcasses partially skinned and/or cut open (facilitated). Elk carcasses lasted a mean 11.9 d (range 3–41), with 60% consumed during the first wk. Deer and pronghorn lasted 5.5 d (range 3–12) and 3.0 d (range 2–4), respectively. Ravens normally arrived by CD 3, Bald Eagles by CD 4, and coyotes by CD 6. Bald Eagles relied on ravens for discovery and sentinel duties, whereas both species depended on coyotes for accessibility. Winter- and road-killed carrion, not canine predation, drove carcass availability. Bald Eagles and coyotes used natural carrion more than human-influenced (road-killed or cut-open) carcasses, whereas Common Ravens were uninhibited by the latter. Removing ungulate carcasses from highway rights-of-way and partially opening them will promote quicker carcass consumption and safer avian scavenging by reducing potential for collisions with passing vehicles. A better understanding of the use of road-killed, large ungulate carrion may facilitate managing this supplemental food source as potential mitigation for other anthropogenic threats to both Bald and Golden Eagles (Aquila chrysaetos), including wind-energy development.

Hybridization, the interbreeding of different species, plays an important role in several evolutionary processes but can have detrimental effects on the species involved, including extinction. We documented increased levels of hybridization between two Clanga species (Lesser Spotted Eagle [Clanga pomarina] and Greater Spotted Eagle [C. clanga]), following a drastic change in the water regime of their habitats in the Biebrza River Valley, Poland. Due to broader combined food-niches of the parent species, we hypothesized that hybrid nestlings should have similar or better nutritional condition when compared to the nestlings of the pure-species pairs. Ptilochronology of the feathers of 119 nestlings (54 Lesser Spotted Eagle, 42 Greater Spotted Eagle, 23 hybrids), and a comparison of the growth and fault bars among the groups suggested a similarity in their nutritional status. However, the number of fault bars present underscored an existing problem in feeding conditions for both pure and hybrid species, which is probably an effect of environmental changes, particularly in the water regime, in the Biebrza River Valley. Our results suggest that hybrid nestlings are potentially available for recruitment into the breeding populations of the two sibling species and their hybrids, although their fertility has yet to be thoroughly investigated. The evolutionary consequences could be a coalescing of the species into one with more generalist environmental requirements that will allow better exploitation of the changing habitats.

Lead poisoning is an important threat to some raptor species, and the primary source of lead is through the ingestion of carcasses that have been shot with lead, which makes scavengers such as vultures particularly vulnerable. We examined the concentrations of lead in blood and bone tissue samples collected throughout the range of the Bearded Vulture (Gypaetus barbatus) in southern Africa. This population is regionally critically endangered and it is not known to what extent lead poisoning may be a threat. Blood lead levels (0.62 ± 0.81 μg dL⁻¹) from six live birds tested in 2017 indicated background levels of exposure to lead. Similarly, five live birds tested in 2009 using a less sensitive method all had blood lead levels <3 μg dL⁻¹. Bone lead levels (11.79 ± 8.34 μg g⁻¹) from eight birds that had died indicated lead exposure and accumulation over time, suggesting that lead may have contributed to their deaths. These levels of lead may be detrimental to the survival and fecundity of this small and declining population. Recommendations to address this threat include banning hunting and culling with lead ammunition, which is the most likely source of this pollutant. Such actions may reduce the population's susceptibility to other threats, which may be compounded by high lead levels, and help ensure the success of planned reintroduction programs.

In October 2017, we opportunistically observed up to 50 Peregrine Falcons (Falco peregrinus) on a ship moored in the western Gulf of Mexico. All birds we aged were juveniles, and they hunted from the ship, frequently perching extremely close to one another (<1 m apart) on cables. Both the number of birds and also the very short inter-individual distances when perching make these observations unusual among the published reports for this species.

We studied the post-fledging movement of two sibling (male and female) juvenile Barbary Falcons (Falco peregrinus pelegrinoides) hatched in Lanzarote (Canary Islands) in 2011 using satellite tracking. Birds were tracked from fledging in May to the end of November, when the signals of both transmitters were lost. During the first 45 d following fledging, both birds behaved similarly and made some flights <70 km away from their nest, on the island where they hatched. However, after the dependence period, we found differences between the individuals. The female made several inter-island movements among the islands of the central archipelago (Gran Canaria, Tenerife and La Gomera) and returned to Lanzarote in October. In contrast, the male stayed close to his natal nest (<100 km) until the end of October, when he was detected in the middle of the Atlantic Ocean >3000 km from the nest, probably using a ship as a perch. Because Barbary Falcon populations of the Canary Islands are listed as “threatened” due to anthropogenic threats (e.g. collisions with human-made structures, illegal shooting, nest-robbing, and hybridization with escaped falconry falcons) and little is known about their post-fledging dispersal movements, more studies of such life-history characteristics, using ringing and remote sensing, are urgently needed to develop management actions for their conservation.

Citizen scientist fifth-graders in Israel helped study and conserve the Lesser Kestrel (Falco naumanni), which until recently was classified as vulnerable. Starting in 1996, students constructed and installed nest boxes, conducted occupancy surveys of nest boxes on their school property, and rescued nestlings that fell out of nests. Their activities also involved the surrounding agro-community. Despite these activities, the occupancy surveys documented a decline of about 58% in the number of occupied nests documented by the students and the families that had nest boxes installed at their homes between 2002 and 2013; however, decreases may have been less severe at the school site itself.

The index includes references to general topics, common names, keywords, and authors. Reference is also made to book reviews and letters. Taxa other than raptors are included where referenced by authors.