David R. Barber

Environmental drivers of variability in the movement ecology of turkey vultures (Cathartes aura) in North and South America.

Variation is key to the adaptability of species and their ability to survive changes to the Earths 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 two continents using satellite tracking coupled with remote-sensing science. Using nearly 10 years of data from 24 satellite-tracked vultures in four distinct populations, we describe an enormous amount of variation in their movement patterns. We related vulture movement to environmental conditions and found important correlations explaining how far they need to move to find food (indexed by the Normalized Difference Vegetation Index) and how fast they can move based on the prevalence of thermals and temperature. We conclude that the extensive variability in the movement ecology of turkey vultures, facilitated by their energetically efficient thermal soaring, suggests that this species is likely to do well across periods of modest climate change. The large scale and sample sizes needed for such analysis in a widespread migrant emphasizes the need for integrated and collaborative efforts to obtain tracking data and for policies, tools and open datasets to encourage such collaborations and data sharing.

Efficacy of Migration Counts for Monitoring Continental Populations of Raptors: An Example using the Osprey (Pandion haliaetus)

ABSTRACT. 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 sampled their populations. We used (1) 3-km-wide and 6-km-wide linear trajectories (migration paths) that connected locations with straight lines and (2) utilization distributions derived from Brownian bridge movement models to estimate the proportions of Ospreys likely to have been detected by watch-sites and watch-sites likely to have detected tagged birds, and to describe the geography of southward migration between North America and South America. The migration path method estimated continental detection rates of 12–23%, with regional maxima of 21–36% in eastern North America. This analysis indicated that 8–20% of all watch-sites could have detected ≥1 of the satellite-tracked Ospreys. The Brownian bridge method estimated that 95% of the utilization distributions of migrating Ospreys in North America intersected ≥1 watch-site and that 89% of all watch-sites intersected ≥1 utilization distribution. Using this method, regional probabilities of detection (mean ± SD) for individuals were estimated to be 33.8 ± 28.8% in eastern, 5.8 ± 6.6% in midwestern, and 4.7 ± 4.9% in northwestern (Pacific coast) North America. Migrating Ospreys appear to concentrate along well-defined, narrow fronts and to use land bridges where available, rather than travel along broad fronts and engage in large water crossings during autumn migration.

What Banding Tells Us About the Movement Ecology of Raptors

Abstract 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 Coopers Hawk (A. cooperii; 3848). We selected birds banded during summer or autumn migration and encountered during winter to investigate movement distances and winter latitudes by sex, age, year banded, banding latitude, and flyway. Female American Kestrels migrated farther than males, but travel distances did not vary by age. Distance moved to wintering sites declined with encounter year for American Kestrels, suggesting that migratory short-stopping may be occurring across North America. Movements of the three species typically showed a chain migration pattern; however, female American Kestrels from the most northern latitudes demonstrated a leapfrog pattern, moving beyond mid-latitude birds to more southerly wintering latitudes. Female American Kestrels and Coopers Hawks moved farther than males, whereas Sharp-shinned Hawk migration distances did not vary by sex. Hatch-year Sharp-shinned and Coopers hawks moved farther than after-hatch-year birds, whereas no age difference was observed for American Kestrels. For all three species, northern-latitude birds moved farther than mid- or low-latitude birds, and low-latitude birds appeared to be largely resident. Distances moved also varied by flyway for both accipiters. LO QUE EL ANILLADO NOS DICE SOBRE LA ECOLOGÍA DEL MOVIMIENTO DE LAS RAPACES Examinamos los registros de encuentro de anillas desde 1920 hasta 2006 para tres rapaces que se anillan comúnmente en América del Norte: Falco sparverius (4707 registros), Accipiter striatus (5256) y A. cooperii (3848). Seleccionamos las aves anilladas durante la migración de verano y otoño y encontradas durante el invierno para investigar las distancias de movimiento y las latitudes de invernada considerando sexo, edad, año de anillado, latitud de anillado y corredor de vuelo. Las hembras de F. sparverius migraron más lejos que los machos, pero las distancias de viaje no variaron con la edad. La distancia recorrida a los sitios de invernada disminuyó con el año de encuentro para F. sparverius, sugiriendo que las paradas migratorias cortas pueden estar sucediendo a lo largo de América del Norte. Los movimientos de las tres especies típicamente mostraron un patrón de migración en cadena; sin embargo, las hembras de F. sparverius de las latitudes más al norte demostraron un patrón de salto de rana, moviéndose más allá que las aves provenientes de latitudes medias hacia latitudes invernales más al sur. Las hembras de F. sparverius y A. cooperii se movieron más lejos que los machos, mientras que las distancias migratorias de Accipiter striatus no variaron según el sexo. Los individuos del primer año de eclosión de A. striatus y A. cooperii se movieron más lejos que las aves de más de un año de eclosión, mientras que no se observaron diferencias de edad para F. sparverius. Para todas estas especies, las aves de latitudes más al norte se movieron más lejos que las aves de latitudes medias o bajas, y las aves de latitudes bajas parecieron ser mayormente residentes. La distancia de movimiento también varió para las dos especies de Accipiter.

A long‐term database on raptor migration at Hawk Mountain Sanctuary, northeastern United States

In most northern temperate regions diurnal birds of prey, or raptors, migrate seasonally between their breeding and wintering grounds. Although their populations can be logistically difficult to survey and monitor because the birds are largely secretive and wide-ranging, most raptors are obligate or facultative soaring migrants that congregate along major thermal and orographic updraft corridors during their seasonal movements. Hawk Mountain Sanctuary (41° N, 75° W), which straddles the Kittatinny Ridge, the southernmost ridge in the Appalachian Mountains in eastern Pennsylvania, witnesses large numbers of migrating raptors during autumn migration. The Sanctuarys long-term migration-count database is the oldest detailed archive on the timing and magnitude of migratory raptors in the world. Records comprise daily (1934–1965) or hourly (1966–present) counts of 18 North American species of raptors migrating past the Sanctuary, as well as detailed weather data recorded from the lookout during autumn migratio...

Winter Ranges of Migratory Turkey Vultures in Venezuela

Abstract We used four Global Positioning System (GPS) satellite transmitters to calculate the wintering ranges of migratory Turkey Vultures (Cathartes aura) that breed in Saskatchewan, Canada, and winter in Venezuela. Between 2007 and 2011, 95% fixed-kernel estimators of range size varied from 54 to 76 731 km2 with an average of 16 814 ± 28 606 km2 (SD), while those calculated with 95% Minimum Convex Polygons ranged from 22 to 46 778 km2 and averaged 9545 ± 17 356 km2. The smallest wintering range was comparable to previously reported range sizes, but our largest wintering range greatly exceeded anything yet recorded. Variation in winter range sizes may be attributed to resource availability, migration costs, and the absence of obligations associated with breeding. Each vulture had a “primary nocturnal roost” to which it returned frequently; each spent more hours (evenings, nights, and mornings) at and within 1 km of such roosts, than it did foraging during midday. Our results increased our understanding ...

Readability of Anodized Aluminum Bands Versus Plastic Darvic Bands on Striated Caracaras in the Falkland Islands (Malvinas)

Bird banding has played a critical role in helping biologists understand the movement ecology and demographics of raptors for almost a hundred years (Thomson 1926, Bildstein 2006). Color-banding, too, has made significant contributions to the field (Varland et al. 2007). Longevity records for banded raptors demonstrate that traditional aluminum bands can remain readable, at least in-hand, for decades (Klimkiewicz and Futcher 1989). Little published information, however, exists on color-band wear and loss. Many researchers (see Varland et al. 2007 for review) have used colored metal bands with alphanumeric codes successfully on raptors. In many cases, the bands have been engraved anodized aluminum bands manufactured by Acraft Sign and Nameplate Co., Ltd., of Edmonton, AB, Canada (Varland et al. 2007). In general, reports to the U.S. Bird Banding Lab by raptor researchers indicate that these bands have proved to be both durable and colorfast on most raptors. Exceptions include reports of considerable wear in anodized color bands fitted (1) on Galapagos Hawks (Buteo galapagoensis) on Santiago Island in the Galapagos, where abrasion by lava rocks rendered many bands unreadable within 4–5 yr (K. Levenstein pers. comm. in Varland et al. 2007), and (2) on Northern Crested Caracaras (Caracara cheriway) in central Florida (J. Morrison pers. comm.), where these bands were used in studies of breeding-site fidelity and species survival (Morrison 1999 and 2003). In addition, a report involving Common Ravens (Corvus corax) banded in and around Jackson Hole, WY (Bedrosian and Craighead 2007), indicated both rapid wear and color loss on anodized aluminum bands that compromised their readability in as few as 9 mo. In this instance, rapid band wear was attributed to the birds’ spending a large part of their time walking on the ground across abrasive substrates including “glacial sand, talus rock, river beds and ice” (Bedrosian and Craighead 2007). Overall, reports suggest that band wear, including anodized aluminum bands, is more common among birds that feed in and around water, particularly if the water is brackish or marine, where the rapid corrosion of aluminum is more prevalent (c.f., Poulding 1954, Hatch and Nisbet 1983, Jehl 1990). Here we report on our experiences using alphanumericcoded anodized aluminum bands and plastic Darvic bands on Striated Caracaras (Phalcoboenus australis), the raptor with the most southerly distribution in the world (Ferguson-Lees and Christie 2001). Striated Caracaras are opportunistic scavenging and occasionally predatory raptors that spend most of the time on the ground in treeless coastal habitats in the Falkland Islands, and Tierra del Fuego (Strange 1996, Meiburg 2006, Catry et al. 2008, RexerHuber and Bildstein 2014). With an estimated global population in the low thousands, the Striated Caracara is considered globally Near Threatened (BirdLife International 2015). One goal of our long-term studies has been to band at least 75% of the overall population of Striated Caracaras on four small islands in the Falklands to better understand the species’ feeding and movement ecology and social behavior. Given that one banded Striated Caracara lived for 16 yr in the wild in the Falklands and that captive birds have lived for 28 yr (Strange 1996), we wanted our bands to be readable for at least 15–20 yr. Eight Striated Caracaras were fitted with anodized aluminum bands in August 2010, eight were banded in December 2010, and an additional 98 were banded in July–August 1Email address: bildstein@hawkmtn.org LETTER