Buteo Swainsoni Research Articles

Serological and Parasitological Prevalence of Toxoplasma gondii in Wild Birds From Colorado

Ground-feeding birds are considered important in the epidemiology of Toxoplasma gondii because they serve as indicators of soil contamination by oocysts, and birds of prey are indicators of T. gondii prevalence in rodents and other small mammals. Cats excrete environmentally resistant oocysts after consuming tissues of T. gondii -infected birds. In the present study, sera and tissues from 382 wild birds from Colorado were tested for T. gondii infection. Antibodies to T. gondii were found in 38 birds with the use of the modified agglutination test (MAT, 1∶25 titer). Tissues (brains, hearts) of 84 birds were bioassayed in mice. Viable T. gondii was isolated from 1 of 1 barn owl (Tyto alba), 1 of 5 American kestrels (Falco sparverius), 1 of 7 ferruginous hawks (Buteo regalis), 1 of 4 rough-legged hawks (Buteo lagopus), 2 of 13 Swainson's hawks (Buteo swainsoni), and 1 of 25 red-tailed hawks (Buteo jamaicensis). This is the first time T. gondii has been isolated from the barn owl, ferruginous hawk, rough-legged hawk, and Swainson's hawk.

Reports of Cooper's Hawks (Accipiter cooperii), Swainson's Hawks (Buteo swainsoni), and Short-tailed Hawks (Buteo brachyurus) in Cuba

REGISTRO DE ACCIPITER COOPERII, BUTEO SWAINSONI Y BUTEO BRACHYURUS EN CUBA Reporto informacion sobre la migracion otonal de Accipiter cooperii, Buteo swainsoni y Buteo brachyurus hacia Cuba. Las observaciones las realice entre el 21 de julio y el 1 de octubre del 2007 en el Cabo de San Antonio, extremo occidental de Cuba. No obtuve evidencias de que las tres especies cruzaran el Estrecho del Yucatan, y todos los individuos que llegaron al Cabo de San Antonio revirtieron su ruta migratoria hacia el este. Los avistamientos realizados sugieren que las especies A. cooperii, B. swainsoni y B. brachyurus son visitantes invernales casuales en Cuba. [Traduccion del equipo editorial]

Health of an ex situ population of raptors (Falconiformes and Strigiformes) in Mexico: diagnosis of internal parasites

Successful programs for ex situ and in situ conservation and management of raptors require detailed knowledge about their pathogens. The purpose of this study was to identify the internal parasites of some captive raptors in Mexico, as well as to verify their impact in the health status of infected birds. Birds of prey were confiscated and kept in captivity at the Centro de Investigación y Conservación de Vida Silvestre (CIVS) in Los Reyes La Paz, Mexico State. For this, fecal and blood samples from 74 birds of prey (66 Falconiformes and eight Strigiformes) of 15 species, juveniles and adults from both sexes (39 males and 35 female), were examined for the presence of gastrointestinal and blood parasites. Besides, the oropharyngeal cavity was macroscopically examined for the presence of lesions compatible with trichomoniasis. Among our results we found that lesions compatible with Trichomonas gallinae infection were detected only in two Red-tailed hawks (Buteo jamaicensis) (2.7%); nevertheless, infected birds were in good physical condition. Overall, gastrointestinal parasites were found in 10 (13.5%) raptors: nine falconiforms (13.6%) and one strigiform (12.5%), which mainly presented a single type of gastrointestinal parasite (90%). Eimeria spp. was detected in Harris's hawk (Parabuteo unicinctus), Swainson's hawk (Buteo swainsoni), Red-tailed hawk (B. jamaicensis) and Great horned owl (Bubo virginianus); whereas trematodes eggs were found in Peregrine falcon (Falco peregrinus) and Swainson's hawk (B. swainsoni). Furthermore, eggs of Capillaria spp. were found in one Swainson's hawk (B. swainsoni), which was also infected by trematodes. Hemoprotozoarian were detected in five (6.7%) falconiforms: Haemoproteus spp. in American kestrel (F. sparverius) and Leucocytozoon spp. in Red-tailed hawk (B. jamaicencis). Despite this, no clinical signs referable to gastrointestinal or blood parasite infection were observed in any birds. All parasites identified were recorded for the first time in raptors from Mexico. Furthermore, this represents the first report for T. gallinae, trematodes, Haemoproteus spp. and Leucocytozoon spp. in raptors from Latin America. Diagnosis and control of parasitic infections should be a part of the routine in health care evaluations for ex situ raptor populations. Finally, this information is also valuable for in situ conservation actions on these birds.

Molecular and Morphological Divergence in a Pair of Bird Species and Their Ectoparasites

In an evolutionary context, parasites tend to be morphologically conservative relative to their hosts. However, the rate of neutral molecular evolution across many parasite lineages is faster than in their hosts. Although this relationship is apparent at the macroevolutionary scale, insight into the processes underpinning it may be gained through investigations at the microevolutionary scale. Birds and their ectoparasitic lice have served as important natural experiments in co-evolution. Here, we compared mitochondrial and morphological divergence in 2 recently diverged avian host lineages and their parasites. Gálapagos hawks (Buteo galapagoensis) are phenotypically divergent from their closest mainland relatives, the Swainson's hawk (Buteo swainsoni). Both species are host to a feather louse species of Craspedorrhynchus (Insecta: Phthiraptera: Ischnocera, Philopteridae). We sequenced the 5′ end of the mitochondrial gene cytochrome oxidase c subunit I (COI) from a set of hawks and lice. Although this fragment allowed unambiguous identification of host and parasite lineages on the islands and the mainland, only a single variable site was present in the 2 hosts, but 2 major Craspedorrhynchus clades divergent by ~10% were recovered that sorted perfectly with host species. We found significant population genetic structure within the Galápagos Craspedorrhynchus lineage. While the host species are highly differentiated phenotypically, the 2 Craspedorrhynchus louse lineages are phenotypically overlapping, although subtle but significant morphological differences exist.

On the origin of the Galápagos hawk: an examination of phenotypic differentiation and mitochondrial paraphyly

Previous phylogenetic hypotheses suggest a sister group relationship between mainland and widespread Buteo swainsoni (Swainson's hawk) and the island archipelago taxon Buteo galapagoensis (Galápagos hawk). We further describe phylogenetic relationships of this clade using molecular data from the mitochondrial control region, and consider the role of niche expansion on phenotype using morphological data from B. galapagoensis, B. swainsoni, and related Buteo jamaicensis (red-tailed hawk). Among 52 unique Buteo haplotypes, phylogenetic analyses support a monophyletic B. galapagoensis clade within a clade of B. swainsoni haplotypes, rendering B. swainsoni paraphyletic with respect to B. galapagoensis. Mitochondrial paraphyly is likely a result of incomplete lineage sorting subsequent to a recent colonization event and exemplifies speciation of peripheral population isolates. Morphological comparisons indicate that metrics associated with prey capture differ significantly between B. galapagoensis and B. swainsoni, but are similar between B. galapagoensis and B. jamaicensis. These results suggest directional selection on B. galapagoensis morphology associated with feeding, possibly an outcome of decreased interspecific competition and change towards a more generalist diet shared by B. jamaicensis. In the B. galapagoensis lineage, our results suggest that genetic drift influences the neutral mitochondrial marker, whereas selection may have driven phenotypic character change.

Foraging by Swainson's Hawks in a Vineyard-Dominated Landscape

ABSTRACT We studied habitat use for foraging by Swainson's Hawks (Buteo swainsoni) within a complex agricultural crop matrix in California's Central Valley to ascertain if vineyards were used for foraging. Central Valley vineyard agriculture has increased recently, especially in areas supporting the highest regional numbers of Swainson's Hawks. There is concern that increased vineyard coverage may reduce the amount of foraging habitat available for Swainson's Hawks, because vineyards have been considered poor foraging habitat for this species, due to the height and density of the vines. In 2002 and 2003, we conducted road surveys to record observations of foraging Swainson's Hawks in relation to agricultural habitats. Using chi-square tests and 95% CIs, we assessed habitat selection for foraging Swainson's Hawks and determined whether habitat use varied throughout the breeding season. Swainson's Hawks used 10 unique habitat types for foraging during the breeding season. Swainson's Hawks used vineyards les...

Where do Swainson's hawks winter? Satellite images used to identify potential habitat

ABSTRACTDuring recent years, predictive modelling techniques have been increasingly used to identify regional patterns of species spatial occurrence, to explore species–habitat relationships and to aid in biodiversity conservation. In the case of birds, predictive modelling has been mainly applied to the study of species with little variable interannual patterns of spatial occurrence (e.g. year‐round resident species or migratory species in their breeding grounds showing territorial behaviour). We used predictive models to analyse the factors that determine broad‐scale patterns of occurrence and abundance of wintering Swainson's hawks (Buteo swainsoni). This species has been the focus of field monitoring in its wintering ground in Argentina due to massive pesticide poisoning of thousands of individuals during the 1990s, but its unpredictable pattern of spatial distribution and the uncertainty about the current wintering area occupied by hawks led to discontinuing such field monitoring. Data on the presence and abundance of hawks were recorded in 30 × 30 km squares (n = 115) surveyed during three austral summers (2001–03). Sixteen land‐use/land‐cover, topography, and Normalized Difference Vegetation Index (NDVI) variables were used as predictors to build generalized additive models (GAMs). Both occurrence and abundance models showed a good predictive ability. Land use, altitude, and NDVI during spring previous to the arrival of hawks to wintering areas were good predictors of the distribution of Swainson's hawks in the Argentine pampas, but only land use and NDVI were entered into the model of abundance of the species in the region. The predictive cartography developed from the models allowed us to identify the current wintering area of Swainson's hawks in the Argentine pampas. The highest occurrence probability and relative abundances for the species were predicted for a broad area of south‐eastern pampas that has been overlooked so far and where neither field research nor conservation efforts aiming to prevent massive mortalities has been established.

Can a ‘wintering area effect’ explain population status of Swainson's hawks? A stable isotope approach

ABSTRACTIt 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 use of wintering areas by breeding populations of Swainson's hawks. We used stable‐hydrogen isotope analysis of feathers to determine whether large flocks of hawks wintering in Argentina consisted of a mixture of individuals from across the North American breeding range or consisted of individuals from discrete breeding populations. We found that flocks of wintering Swainson's hawks consisted of a mixture of individuals. The lack of connectivity between populations of breeding and wintering hawks suggests that high wintering mortality, either natural or human‐induced, is unlikely to have direct consequences on a single breeding area in North America. The demographic effects of winter mortality should be ‘diluted’ across the entire breeding range of Swainson's hawks.

HYBRIDIZATION AMONG BUTEOS: SWAINSON'S HAWKS (BUTEO SWAINSONI) × RED-TAILED HAWKS (BUTEO JAMAICENSIS)

We report three cases of hybridization between wild Swainson's Hawks (Buteo swainsoni) and Red-tailed Hawks (B. jamaicensis) identified by using nuclear and mitochondrial DNA markers. The hybrid individuals were field-identified as Swainson's Hawks and sampled from Alberta, Canada (n = 2) and Utah, USA (n = 1). Nineteen nuclear microsatellite loci were used in a factorial correspondence analysis to create genotypic clusters of 468 Red-tailed and 357 Swainson's hawks. Three suspected hybrids were identified by an intermediate genetic position between the genotypic clusters of the two species, indicating a hybridogenetic composition. We examined mitochondrial control region sequence data to identify the maternal background of the putative hybrids; two of the hybrid specimens had Red-tailed Hawk mtDNA haplotypes and the third a Swainson's Hawk haplotype. These results suggest that hybridization between these two species may occur in their shared breeding range and can result in reciprocal hybrid offspring, barring any social, behavioral, or biological isolating mechanisms.

Population structure and genetic diversity in Swainson’s Hawks (Buteo swainsoni): implications for conservation

Swainson’s Hawks (Buteo swainsoni) are large raptors with a breeding distribution extending across much of western North America where they were historically considered one of the most abundant raptors. Swainson’s Hawks have declined precipitously in many parts of their range during the 20th century, and the historical range in California has been much reduced. In the Central Valley of California (CV), Swainson’s Hawks exhibit behavioral and morphological characteristics apparently different from other regions. To describe the genetic diversity and population structure of Swainson’s Hawks throughout their range, 19 microsatellite loci and 416 base pairs of the mitochondrial control region were analyzed. Microsatellite diversity appears high throughout the contemporary range. A Bayesian model-based analysis of microsatellite genotypes revealed clusters associated with the CV and the Great Basin/Great Plains region of North America (GBGP) with overlap between regions. F ST estimates suggest limited differentiation among Swainson’s Hawks with isolation by distance. A heterozygote excess indicated a recent reduction in effective population size of Swainson’s Hawks across all regions. Control region data revealed no population structure and provided evidence of historic population expansion in the GBGP. In the CV a weaker signature of population expansion was detected, possibly altered by recent declines. While genetic data suggests recent gene-flow across regions, apparent differences between the CV and GBGP in traits with potential fitness consequences (migratory behavior and morphology) along with marked decline in numbers in California call for careful conservation, management, and monitoring of Swainson’s Hawks in the CV.

First Detection of Bacillus anthracis in Feces of Free-ranging Raptors from Central Argentina

Prevalence of anthrax spores in feces of raptors was determined from samples collected in November-December 2000 and April-May 2001 in an agricultural region of Santa Fé province, Argentina. Feces were tested from 48 birds of six raptor species. One of 14 chimango caracaras (Milvago chimango) and one of eight road-side hawks (Buteo magnirostris) tested positive. The prevalence of Bacillus anthracis spores in feces for the six species was 4% (n=48). The prevalence was 7% (n=14) for chimango caracaras, 13% for road-side hawks (n=8), and 0% for the remaining species (Burrowing owl [Speotyto cunicularia] [n=17], Swainson's hawk [Buteo swainsoni] [n=3], Aplomado falcon [Falco femoralis] [n=2], and American kestrel [Falco sparverius] [n=4]). Grouped by their feeding habits, prevalence for scavenger species was not significantly different than for predators (7% vs. 3%, P>0.999). This study provides evidence that in central Argentina scavenger and non-scavenger raptors may have a role in the epidemiology of anthrax. Long-term studies to determine the extent of this potential involvement in the epidemiology of anthrax in central Argentina are required.

Development of 19 microsatellite loci for Swainson's hawks (Buteo swainsoni) and other buteos

AbstractWe developed 26 Swainson's hawk (Buteo swainsoni) microsatellite primers from CA, AAT, CATC and GAGAA enriched genomic libraries. Primers were tested in 357 Swainson's hawks from western North America as well as seven other Buteo species. These markers will have broad application in investigations of Buteo population structure and genetic diversity.

A re-evaluation of evidence raises questions about the fasting migration hypothesis for Swainson’s Hawk (Buteo swainsoni)

We examined the fasting migration hypothesis for Swainson’s Hawks (Buteo swainsoni) by estimating the length, duration, and speed of the migration between North and South America and measuring changes in their body masses at various times throughout the year. We instrumented 34 adult Swainson’s Hawks with satellite radios on their breeding grounds in western North America to determine the duration, length, and speed of the migration. Migrating south at 188 km/day, it took Swainson’s Hawks 51 days to complete their 13504 km migration to their austral summer grounds. Averaging only 150 km/day on their return migration, it took them 60 days to complete the shorter 11952 km migration back to North America. Adult male and female Swainson’s Hawks had average body masses of 872 g and 1131 g, respectively, when they departed from North America in September and their body masses upon arrival in Argentina averaged 759 g for adult males and 933 g for adult females, indicating they lost only an average of 18% of their body masses during migration. Adult male and female Swainson’s Hawks had body masses of 792 g and 1013 g, respectively, in February prior to their departure from Argentina and they returned to the breeding grounds in North America weighing 802 g and 1087 g in April. Our results indicate that the fasting migration model does not predict the actual body masses of Swainson’s Hawks during the migration season and it should be modified to account for either lower energy expenditures during migration or the possibility that the birds use a stopover strategy during migration, feeding and regaining, or maintaining, fat stores along the migration route.

ECOLOGY AND GENETICS OF AN ISOLATED POPULATION OF SWAINSON'S HAWKS IN ILLINOIS

ABSTRACT Swainson's Hawks (Buteo swainsoni) are listed as state-endangered in Illinois but virtually nothing is known about the small population persisting in the northeastern corner of the state. This population is separated from the nearest western populations by about 355 km. We estimated the size of the Illinois population at 10–16 adults in 2003 and conducted a preliminary study of the genetic relationship between the Illinois population and birds from Idaho near the western edge of their geographic range. We found slight but significant differentiation between the two populations. Band-sharing was high within (80–85%) and between (81%) populations suggesting fairly recent (within 150 yrs) isolation of the Illinois population.

Demography of Swainson's Hawks Breeding in Western Canada

Abstract Our objective was to estimate demographic parameters and population trends for Swainson's hawks (Buteo swainsoni) breeding in southeast Alberta and southwest Saskatchewan, Canada, from 1972 to 2003. We assembled mark–resighting–recovery histories of 6,606 banded Swainson's hawks for a joint analysis of survival and resighting probability, including band-reporting rate and fidelity of animals, following Burnham's joint resighting–recovery model provided in program MARK. Our best-fitting survival model specified age-related variation in survival, resighting probability, and fidelity, and it specified age-by-temporal variation in nestling survival and adult resighting probability. From estimated survival rates and previously published data on reproduction, for the period 1973–1996 we estimated the population's finite rate of increase, λ, to be 0.996 (95% CI: 0.945–1.057). We believe that population limitation of Swainson's hawks is primarily related to the influence of prey availability on brood siz...

Role of exotic tree stands on the current distribution and social behaviour of Swainson's hawk, Buteo swainsoni in the Argentine Pampas

AbstractAim The Argentine Pampas was extensively and abruptly altered by European colonization. Between 1880 and 1885 the indigenous human inhabitants were completely displaced, and native grasslands were replaced by exotic pasture plants and crops. One of the most important ecological changes in the Pampas landscape, the introduction of tall exotic tree species, has received little attention, and its effect on wildlife has never been assessed. We have made an intensive survey of habitat use of Swainson's hawk, Buteo swainsoni in its most important non‐breeding quarters, the Pampas of Argentina, aiming to characterize the sites used by hawks for communal roosting.Location Pampas grasslands, Argentina.Methods We surveyed 30,000 km of roads by car during the austral summer from 2001 to 2004, covering the main non‐breeding area occupied by Swainson's hawks. Their roost sites were located by direct observation of birds roosting in tree stands close to the roads, by surveying potential roost sites around places where groups of pre‐ and post‐roosting hawks were recorded, and by gathering information from local farmers.Results Swainson's hawks exclusively used stands of exotic tree species for roosting. Eucalyptus viminalis was present in all 34 roosts surveyed, and in 59% of them it was the only species present. The remaining exotic tree species were the Siberian elm, Ulmus pumila, pines (Pinus spp.) and cypress (Cupressus spp.). Flock sizes at roost sites were unusually high for a raptor, with an average of 658 individuals (range 8–5000 hawks, n = 27 flocks).Main conclusions The introduction of exotic trees may have resulted in the expansion of the suitable habitat for Swainson's hawks, permitting a recent colonization of the Argentine Pampas. Tree stands may have also changed the communal roosting behaviour of this raptor, by virtue of their providing new structural elements in a region that almost completely lacked trees prior to European occupation.

FIRST KNOWN SPECIMEN OF A HYBRID BUTEO: SWAINSON'S HAWK (BUTEO SWAINSONI) × ROUGH-LEGGED HAWK (B. LAGOPUS) FROM LOUISIANA

Abstract We report a specimen that appears to be a hybrid between Swainson's Hawk (Buteo swainsoni) and Rough-legged Hawk (B. lagopus), which, to our knowledge, is the first hybrid specimen for the genus. There are few reports of hybridization between Buteo species, most of which have been observations of interspecific nesting pairs. The specimen described herein was collected in Louisiana and initially identified as a Rough-legged Hawk because of its feathered tarsi and the dark bellyband and carpals. A DNA sequence from the maternally inherited mitochondrial ND6 gene was identical to a published sequence for Swainson's Hawk. Nuclear DNA sequences from two introns contained only five variable sites among a panel of five potential parental taxa, but the hybrid sequence was most consistent with parentage by Rough-legged and Swainson's hawks. The feathered tarsi of the hybrid strongly suggested that the father was either a Rough-legged or Ferruginous hawk (B. regalis), the only North American raptors other ...

Hunting success of wintering Swainson's hawks: environmental effects on timing and choice of foraging method

We examined the predatory behavior of Swainson's hawks (Buteo swainsoni Bonaparte, 1838) wintering in the Argentine pampas. Aerial and ground foraging were the main hunting methods employed by hawks in this region. The overall hunting success of hawks preying on insects was 50% and age-related differences in hunting success were not significant. The Swainson's hawks, however, hunted more successfully in the air (65% of prey capture attempts) than on the ground (42%). Aerial hunting while soaring was the most successful hunting method based on the number of prey captured per energy unit. Based on the analysis of prey consumed by hawks during the study period, grasshopper species with poor flight capabilities were available in the air as a consequence of the vertical air motion. With regards to daily activity patterns, the time that a hawk spent using each hunting method was not proportional to the cost ratio associated with each method. Hawks foraged in the air only during midday hours when weather conditions permitted the formation of thermals. Thus, the use of soaring flights and the availability of prey in the air were constrained by the physical environment, and hawks could only exploit airborne food sources during limited periods of the day.

Hailstorms as a Cause of Mass Mortality of Swainson's Hawks in Their Wintering Grounds

We describe a mass mortality event of wintering Swainson's hawks (SH, Buteo swainsoni) in central Argentina during November 2003. One hundred thirteen SH were found dead as a consequence of a single hailstorm. In addition, 14 hawks with severe injuries were recovered alive, but only 10 of these survived 1 wk later. Another 45 dead birds of 11 species were collected in the area. Interviews with local land-owners conducted in other areas of the SH wintering grounds provided further evidence of past hailstorm-related mortality involving SH, suggesting that such events commonly occur in the Argentine Pampas. This potential cause of mass mortality of SH wintering in agricultural areas of Argentina may be significant when added to the increased mortality associated with poisoning events during the last decade.

KNEMIDOKOPTES IN A SWAINSON'S HAWK, BUTEO SWAINSONI

A male Swainson's hawk (Buteo swainsoni) at a rehabilitation facility in Colorado was presented with severe crusting of the skin on the medial thighs and caudal ventral body. Male and female Knemidokoptes mites were found on a cellophane tape preparation of the affected area. The hawk's clinical signs resolved with treatment with ivermectin administered at 200 microg/kg, i.m., every 10 days for three treatments.