Keith L Bildstein

Hawk Mountain Sanctuary · Conservation science

The demography of, and factors that influence these metrics, are largely unknown for most vultures in the Americas. Survivorship of Turkey Vultures (Cathartes aura) may be influenced by landscape heterogeneity and human disturbance. We quantified the effects of landscape composition (Shannon's diversity index) and configuration (contagion, edge den...

The demography of, and factors that influence these metrics, are largely unknown for most vultures in the Americas. Survivorship of Turkey Vultures (Cathartes aura) may be influenced by landscape heterogeneity and human disturbance. We quantified the effects of landscape composition (Shannon's diversity index) and configuration (contagion, edge den...

Avian scavengers perform vital ecosystem services by removing waste and slowing disease, yet few details are known about the process of carcass depletion, or the role of social interactions among groups of scavengers. The striated caracara (Phalcoboenus australis) is a social scavenging falconid of the Falkland Islands, whose boldness and reliance...

Annual movements have been widely described for birds migrating across the Americas and between Eurasia and Africa, yet relatively little information exists for intra-African migrants. Identifying the areas used throughout a species annual cycle by understanding migratory patterns and settlement areas during breeding and non-breeding seasons is ess...

Summary of annual movement data obtained from the 13 adult Black Harriers marked with GPS-GSM or PTT tracker devices and followed in south-western South Africa during the 2008–2016 period. (DOCX)

More detailed summary data for the identified breeding and non-breeding settlement areas used by the 13 adult Black Harriers marked with GPS-GSM or PTT tracker devices followed in south-western South Africa during the 2008–2016 period. (DOCX)

Aim Animal movement is an important determinant of individual survival, population dynamics and ecosystem structure and function. Nonetheless, it is still unclear how local movements are related to resource availability and the spatial arrangement of resources. Using resident bird species and migratory bird species outside the migratory period, we...

With long coastlines and some of the world’s most important rivers, mountain ranges, high-altitude plateaus, and islands, Asia is the largest and most populous continent in the world (Lyde 1904; Spencer 1954; Population Reference Bureau 2016). Asia supports all major terrestrial ecosystems and all major climatic types (Galloway et al. 1998; Braimoh...

The phenomenon of raptor migration has fascinated humanity since antiquity and with good reason. As one of the most behaviorally flexible aspects of raptor biology, migration has allowed this trophic lineage to prosper in ways that few terrestrial top predators have been able to achieve.

Background The extent to which seasonal changes in food availability affect small-scale movements in free-ranging populations of birds of prey is relatively little studied. Here we describe a seasonal “micro-migration” of a farm-island population of striated caracaras (Phalcoboenus australis) in the Falkland Islands in response to seasonal changes...

Animals regularly return to locations such as foraging patches, nests, dens, watering holes, or movement corridors, and these revisited locations are often sites of ecological significance. Analyzing the temporal and spatial pattern of revisitation can lead to important insights into the life history and ecology of populations. We introduce the R p...

Populations of “urban” raptors are increasing globally. Trained falcons are now being flown in city golf courses to scare off geese in hopes of reducing accumulated droppings along the fairways. In both the Old World and New, tens of thousands of vultures rummage through urban garbage dumps in search of humans’ leftovers. In Spain, lesser kestrels...

Climate change can affect the distribution, abundance, and phenology of organisms globally. Variations in the timing of passage during autumn and spring migration can have consequences at individual and population levels. We assessed whether global climatic indexes and increasing air temperature over a 28 yr period were concurrent with shifts in th...

Hooded Vultures Necrosyrtes monachus are critically endangered but little is known of their year-round use of nests or whether other species usurp Hooded Vulture nest sites. We investigated visitation rates by Hooded Vultures and other species (including potential nest predators and usurpers) to examine their effect on Hooded Vulture breeding succe...

Global change can affect several aspects of bird biology, including population size and migration timing. We used count data collected during 25 years (1990-2014) at Hawk Mountain Sanctuary, a raptor migration watch-site in eastern Pennsylvania, to investigate population changes in Ruby-throated Hummingbirds (Archilochus colubris) and the timing of...

Relatively little is documented about nest material theft in vultures. We used camera traps to monitor Hooded Vulture Necrosyrtes monachus nests for a year. We report camera trap photographs of a starling Lamprotornis sp. removing what appeared to be dung from an inactive Hooded Vulture nest on Cleveland Game Reserve, northeastern South Africa, in...

Birds migrating across the Himalayan region fly over the highest peaks in the world, facing immense physiological and climatic challenges. The authors show the different strategies used by birds to cope with these challenges. Many wetland avian species are seen in the high-altitude lakes of the Himalayas and the adjoining Tibetan Plateau, such as B...

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 t...

Both wing size and wing shape affect the flight abilities of birds. Intra and inter-specific studies have revealed a pattern where high aspect ratio and low wing loading favour migratory behaviour. This, however, have not been studied in soaring migrants. We assessed the relationship between the wing size and shape and the characteristics of the mi...

Movebank Data Repository

Capsule: Red-footed Falcons Falco vespertinus migrating from northern Kazakhstan proceed west before heading south to Africa; their northbound travel follows a different route with passage close to shooting hotspots in the Mediterranean.Aim: To use tracking and ringing data to document for the first time the migration of globally threatened Red-foo...

Knowledge of a species’ geographic distribution is crucial to assessing its vulnerability. It is also important to know if protected areas provide effective protection for raptor species. Here, we examine the species richness (S) patterns, factors predicting S and the effectiveness of protected areas (EPA) in the conservation of diurnal raptors in...

Basic ecological information is still lacking for many species of African vultures. The Hooded Vulture Necrosyrtes monachus is known as a rare breeding resident in north-eastern South Africa. This study set out to monitor the nests of Hooded Vultures and, secondarily, White-backed Vultures Gyps africanus in the Olifants River Private Nature Reserve...

Birds use atmospheric updrafts to subsidize soaring flight. We observed highly variable soaring flight by Black Vultures (Coragyps atratus) and Turkey Vultures (Cathartes aura) in Virginia, USA, that was inconsistent with published descriptions of terrestrial avian flight. Birds engaging in this behavior regularly deviated vertically and horizontal...

Tracking individual animals using satellite telemetry has improved our understanding of animal movements considerably. Nonetheless, thorough statistical treatment of Argos datasets is often jeopardized by their coarse temporal resolution. State-space modelling can circumvent some of the inherent limitations of Argos datasets, such as the limited te...

Climatic factors influence migration behavior in both short-and long-distance migratory birds. The Broad-winged Hawk (Buteo platypterus) is a long-distance migrant that exhibits a regular calendar-like migration pattern, with some interannual variability during both the northbound and southbound migrations. We examined the relationship between the...

We study the effects of heat loss and nest site quality on fecundity in a chinstrap penguin (Pygoscelis antarctica) colony on Deception Island, Antarctica. During the austral summers of 1990–1991, 1993–1994, and 1995–1996, 441 randomly selected nests were analyzed. Penguins breeding in the center of subcolonies hatched significantly earlier and had...

Satellite tracking is an invaluable tool in the study of bird movements. However, the normally small sample size it involves makes it difficult to obtain data spanning the entire range of migratory behaviour found in particular populations. We recently reported that Spanish immature Short-toed Snake Eagles leave their winter quarters in sub-Saharan...

Variation is key to the adaptability of species and their ability to survive changes to the Earth's climate and habitats. Plasticity in movement strategies allows a species to better track spatial dynamics of habitat quality. We describe the mechanisms that shape the movement of a long-distance migrant bird (turkey vulture, Cathartes aura) across t...

Every autumn, large numbers of raptors migrate through geographical convergence zones to avoid crossing large bodies of water. At coastal convergence zones, raptors may aggregate along coastlines because of convective or wind conditions. However, the effect of wind and thermal convection on migrating raptors may vary depending on local landscapes a...

The ongoing global decline in vulture populations raises major conservation concerns, but little is known about the factors that mediate scavenger habitat use, in particular the importance of abundance of live prey versus prey mortality. We test this using data from the Serengeti-Mara ecosystem in East Africa. The two hypotheses that prey abundance...

ÁREAS DE INVERNADA DE INDIVIDUOS MIGRANTES DE CATHARTES AURA EN VENEZUELA Utilizamos cuatro transmisores satelitales de Sistema de Posicionamiento Global (SPG) para calcular las áreas de invernada de individuos de Cathartes aura que se reproducen en Saskatchewan, Canadá e invernan en Venezuela. Entre 2007 y 2011, 95% de los estimadores de kernel fi...

Striated caracaras occur only on the Falkland Islands and the outer islands of southern Chile and Argentina. In summer, the species associates with seabirds and seals and depends heavily upon them for food. The winter diet is less well understood. We studied the diet of 90–130 mainly juvenile and sub-adult striated caracaras overwintering at a farm...

We examined banding encounter records from 1920 to 2006 for three raptors that are commonly banded in North America: American Kestrel (Falco sparverius, 4707 encounters), Sharp-shinned Hawk (Accipiter striatus; 5256), and Cooper's Hawk (A. cooperii; 3848). We selected birds banded during summer or autumn migration and encountered during winter to i...

The future of conventional banding in raptor science depends upon the types of questions asked by scientists working in the field, and the extent to which banders and researchers continue their trapping and banding efforts. Traditionally, banding data have played two important roles in raptor science: assessing demographic statistics, including age...

The Golden Eagle (Aquila chrysaetos) population in North America is declining (Hoffman and Smith 2003, Smith et al. 2008). This species is enigmatic, indicative of broad conservation value (Sergio et al. 2005), and, for the most part, poorly known. Populations west of the Mississippi River in the lower 48 states number approximately 21,000–35,000 i...

Ecology Letters (2011) Soaring birds migrate in massive numbers worldwide. These migrations are complex and dynamic phenomena, strongly influenced by meteorological conditions that produce thermal and orographic uplift as the birds traverse the landscape. Herein we report on how methods were developed to estimate the strength of thermal and orograp...

Understanding the movements of animals is pivotal for understanding their ecology and predicting their survival in the face of rapid global changes to climate, land use, and habitats, thus facilitating more effective habitat management. Migration by flying animals is an extreme form of movement that may be especially influenced by weather. With sat...

We used Global Positioning System (GPS) satellite transmitters to estimate the breeding home ranges of Turkey Vultures (Cathartes aura) in Saskatchewan, Canada from 2005 to 2009. Breeding ranges calculated using 95% Minimum Convex Polygons (MCP) ranged from 47 to 953 km2 and averaged (± SD) 371 ± 340 km2. Fixed-kernel home ranges (95%) ranged from...

Island faunas have played central roles in the development of evolutionary biology and ecology. Birds are among the most studied organisms on islands, in part because of their dispersal powers linked to migration. Even so, we lack of information about differences in the movement ecology of island versus mainland populations of birds. Here we presen...

18 nest sites have been studied in 2009-2010. Distances between the nests in Yerevan largely reflect the irregular distribution and sizes of suitable wooded habitats within the city. In Meghri region average distance between the active nests was 739 m in 2009 and 532 m in 2010, with minimum distances of 203 (2009) and 193 m. Levant Sparrowhawk in A...

Recent research has confirmed the efficacy of migration monitoring to estimate trends in the populations of raptors sampled at traditional watch-sites. We used autumn satellite tracks of 57 adult Ospreys (Pandion haliaetus) captured on the breeding range in North America between 1995 and 2000 to assess the extent to which migration monitoring sampl...

The winter population ecology of American Kestrel (Falco sparverius), one of the most abundant and widely distributed raptors in North America, is poorly understood. We systematically searched a 225-km2 area in Cape Coral, southwestern Florida, for American Kestrels during 14 winters (1 Dec–15 Mar, 1994–2008) to measure their annual apparent surviv...

Migratory bird needs must be met during four phases of the year: breeding season, fall migration, wintering, and spring migration; thus, management may be needed during all four phases. The bulk of research and management has focused on the breeding season, although several issues remain unsettled, including the spatial extent of habitat influences...

Our understanding of migratory birds' year-round ecology and evolution remains patchy despite recent fundamental advances. Periodic reviews focus future research and inform conservation and management; here, we take advantage of our combined experiences working on Western Hemisphere avian migration systems to highlight recent lessons and critical g...

The Shikra Accipiter badius is a widespread Accipiter with a predominantly Asian and African distribution. In the Transcaucasus, until current investigation, the Shikra was known for Azerbaijan. Our observations in Yerevan (capital) have revealed two breeding pairs of the species, thus extending the known breeding range of A. b. cenchroides west to...

The Broad-winged Hawk (Buteo platypterus) breeds in eastern and central Canada and the United States, and winters in Central America and northern and central South America. Birders and ornithologists count migrating Broad-winged Hawks at dozens of traditional watch sites throughout the northeastern United States. We modeled counts of migrating Broa...

The flight behaviour of Griffon Vultures Gyps fulvus was studied at a major migration bottleneck, the Strait of Gibraltar in southernmost Spain, during the autumns of 2004 to 2007. The 14-km-wide sea channel significantly impeded the southern migration of the species into Africa, with many birds attempting repeated passage for weeks before crossing...

Biological field stations are distributed throughout North America, capturing much of the ecological variability present at the continental scale and encompassing many unique habitats. In addition to their role in supporting research and education, field stations offer legacies of data, specimens, and accumulated knowledge. Such legacies often prov...

Resumimos y discutimos observaciones recientes de migraciones nocturnas de Pandion haliaetus. En el otoño de 2004, desde la plataforma de observación (elevación 320 m) del edificio Empire State en la ciudad de Nueva York se realizaron dos avistamientos nocturnos de individuos migrando hacia el sur. De igual forma, el monitoreo satelital ha revelado...

We develop individual-based movement ecology models (MEM) to explore turkey vulture (Cathartes aura) migration decisions at both hourly and daily scales. Vulture movements in 10 migration events were recorded with satellite-reporting GPS sensors, and flight behavior was observed visually, aided by on-the-ground VHF radio-tracking. We used the North...

Abstract – Raptors are popular birds and they often serve as flagship species for broader conservation efforts. Unfortunately, they are secretive, wide-ranging, and area-sensitive species that can be logistically difficult and financially prohibitive to survey and monitor. Raptors often congregate during migration however, and one cost-effective wa...

It has been suggested that declines in breeding populations of Swainson's hawks (Buteo swainsoni) in California, Oregon, and Nevada may be due to differential mortality of hawks on their wintering grounds. Although massive mortality incidents reported on the wintering grounds partially support this suggestion, there are no data showing differential...

We describe predictable nocturnal soaring flight in Turkey Vultures (Cathartes aura) feeding at a landfill in eastern Pennsylvania. Birds feeding at the landfill returned to their roosts each evening by gaining altitude while soaring in thermals above flared methane vents at the site. Our results highlight behavioral plasticity in this species, whi...

Standardized English-language and French-language common names for Latin American raptors already exist. We use criteria outlined below to create a series of standard Spanish common names for raptors occurring in the region. Standardized Spanish common names should be useful to conservation biologists and educators that wish to use these often char...

We compared migrating behavior of Broad-winged Hawks (Buteo platypterus) at two sites along their migration corridor: Hawk Mountain Sanctuary in eastern Pennsylvania and the Kekoldi Indigenous Reserve in Limon, Costa Rica. We counted the number of times focal birds intermittently flapped their wings and recorded the general flight type (straight-li...

The Llanos of Venezuela is a 275 000-km2 freshwater wetland long recognized as an important habitat for waterbirds. However, little information exists on the raptor community of the region. We conducted raptor surveys in the Southwestern and Western Llanos during 2000-02 and detected 28 species representing 19 genera. Overall, areas of the Llanos t...

A long-term, volunteer-based nest-box program for American Kestrels (Falco sparverius) breeding in eastern Pennsylvania was evaluated to identify ways to increase the efficiency of the program and to identify general principles that can be used to improve long-term conservation efforts for other nest-box programs. Between 1993 and 2002, Hawk Mounta...

Raptors are secretive, area-sensitive predators whose populations can be logistically difficult and financially prohibitive to monitor. Many North American popula- tions of raptors are migratory however, and on mig- ration raptors are frequently counted at traditional migration watchsites. Experiences at Hawk Mountain Sanctuary (HMS) and elsewhere...

Counts of migrating Blue-tailed Bee-eaters Merops philippinus and Bluethroated Bee-eaters M. viridis, as well as five raptor species were made in March 2000 and March 2001 at Tanjung Tuan, a coastal migration watchsite in western Malaysia. Totals of 2226 bee-eaters (12.9 bee-eaters h-1) and 11 441 raptors (66.5 raptors h-1) were counted. The Blue-t...

Daily counts of migrating raptors were made on 43 days between 27 September and 9 November 2003 near the city of Chumphon in south-east Thailand. Overall, 170,665 migrating raptors of 15 species were counted during 378 hours of observation (452 birds/hour).The counts of five raptor species (Black Baza Avecida leuphotes ,O riental Honey-buzzard Pern...