White-tailed Hawk Research Articles

Breeding ecology of White-tailed Hawks (Geranoaetus albicaudatus) on Texas barrier islands

Breeding ecology of White-tailed Hawks (Geranoaetus albicaudatus) on Texas barrier islands

Nest site selection of White-tailed Hawks (Geranoaetus albicaudatus) on Texas barrier islands

The distribution of the White-tailed Hawk (Geranoaetus albicaudatus) in the United States is restricted to the prairies and savannas of the Gulf Coastal Plain of Texas. Although listed as a state threatened species, it remains one of the least studied raptors in North America. It appears to reach high densities on some Texas barrier islands despite the island vegetation communities being structurally simple and providing few nesting substrates. We compared vegetation and landscape characteristics for sets of White-tailed Hawk nest sites and random sites on 3 Texas barrier islands (Matagorda, Mustang, and North Padre) representing a gradient of low to high human presence and impact. We constructed model sets consisting of vegetation and landscape features measured at a random subsample of nest sites and random sites, then assessed model sets with logistic regression. Our best constructed model correctly differentiated 83% of nest sites from random sites on Matagorda Island, 70% on Mustang Island, and 50% on North Padre Island. Overall, it appears that the structure of nest substrates was important to White-tailed Hawk nest-site selection: shrubs categorized as densely structured with or without thorns accounted for 78% of nest substrates compared to only 13% of paired, random potential substrates. The most frequently selected nest substrates overall were yaupon (Ilex vomitoria; 43%) and Macartney rose (Rosa bracteata; 24%). If White-tailed Hawks are to be conserved on the barrier islands, a balance will need to be found between continued anthropogenic development, maintenance of habitat patches, and availability of suitable nesting substrates.

Effects of Broadcasting Calls on Detection Probability in Occupancy Analyses of Multiple Raptor Species

For population studies that rely on aural or visual observations of individuals, methods that induce a detectable response can greatly improve sample sizes and reduce costs. Numerous authors have reported improved detections using broadcast surveys in forested areas for various species of raptors; however, to our knowledge, none have attempted to quantify the effects of broadcast surveys on the detection probability (p) in the context of an occupancy study for multiple species. Our objective was to determine whether broadcasting conspecific and heterospecific calls (broadcast surveys) would increase p of raptor species compared to passive surveys. This comparison was accomplished by estimating p during both types of surveys using a multiscale occupancy framework. We conducted 8400 surveys for Cooper's Hawk (Accipiter cooperii), Swainson's Hawk (Buteo swainsoni), White-tailed Hawk (Geranoaetus albicaudatus), Harris's Hawk (Parabuteo unicinctus), Red-tailed Hawk (Buteo jamaicensis), and Great Horned Owl (Bubo virginianus) in 2015 and 2016 in south Texas. We conducted 10-min passive surveys in both years, 10-min broadcast surveys in 2015 including calls from each of the target hawk species, and 10-min broadcast surveys in 2016 using calls from Great Horned Owls. Our results suggest that p is improved with multiple-hawk broadcast surveys (0.16, SE 0.04) over passive surveys (0.04, SE 0.02) for Harris's Hawks; p was not affected in broadcast surveys for the other hawk species considered. Great Horned Owls had a higher p during broadcast surveys using Great Horned Owl calls (0.35, SE 0.04) than during passive surveys (0.19, SE 0.02). Our results do not support the use of broadcast surveys to improve the detection probability of multiple species of hawks. However, our results do indicate that using broadcast surveys for occupancy studies focused on Harris's Hawks or Great Horned Owls should significantly reduce the effort required over passive surveys, resulting in improved power and reduced costs.

Understanding the Relationship Between Northern Bobwhite Mortality and Raptor Migration in South Texas (Poster Abstract)

The fall and spring migration routes of numerous raptor species converge in the Rio Grande Plains ecoregion of Texas resulting in a high seasonal diversity and abundance of raptors. Raptors are believed to be an important source of mortality for northern bobwhite (Colinus virginianus). Because of the economic importance of bobwhites and the high concentration of raptors in south Texas, we investigated the relationship between bobwhite mortality and raptor abundance. Our objectives were to document raptor diversity and abundance, correlate bobwhite mortality with raptor abundance, and correlate ambient temperature with raptor abundance.We monitored radiomarked bobwhites (n = 164) biweekly during September–February 2000–01 in Brooks County, Texas. We conducted raptor surveys bimonthly during October–February 2000–01 between 1100 and 1500 hours along a 24-km road. We documented a total of 96 bobwhite mortalities. Raptors accounted for 16 % of the mortalities, with 43% by mammals, 13% unknown predator, and 28% hunter. We observed a total of 310 raptors, representing 15 identified species. Red-tailed hawk (Buteo jamaicensis) and white-tailed hawk (Buteo albicaudatus) comprised a large percentage (38%) of the raptors observed. A weak correlation (r = - 0.11) existed between raptor abundance and total bobwhite mortality. A stronger correlation (r = 0.86) existed between Accipter abundance and raptor depredation of bobwhites. We detected a relatively strong negative correlation (r = -0.65) between raptor abundance and ambient temperature. Our limited data suggest that general raptor abundance may not be a strong indicator of actual bobwhite mortality, and that it may be erroneous to infer that a high abundance of raptors results in a high mortality of bobwhites. Understanding the relationship between bobwhite and raptors will involve determining species-specific migration timing and numbers.

First record of the Yellowish Pipit in Acre with notes on other grassland birds in southwestern Amazônia

This paper presents the first record of the Yellowish Pipit ( Anthus lutescens ) in the Brazilian state of Acre. This record represents the westernmost record of the species in Brazil and provides evidence of its expansion into the southwestern Amazon basin. We also present information on the occurrence of other bird species, typical of grasslands and other open habitats, e.g., the Burrowing Owl ( Athene cunicularia ), the White-tailed Hawk ( Geranoaetus albicaudatus ), the Southern Lapwing ( Vanellus chilensis ) and the Southern Caracara ( Caracara plancus ). These species have encroached southwestern Amazonia following environmental changes caused by human activities, such as the construction of highways and the conversion of the rainforest into cattle pasture. Keywords: Aves, Anthus lutescens , Motacillidae, open habitats, range extension.

Temporal Fluctuations in Raptor Abundances in Grasslands of Southeastern South America

Abstract We conducted 44 roadside surveys on grasslands landscapes of southern Brazil and Uruguay to study temporal changes in raptor abundance. Each route was surveyed twice in fall/winter and twice in spring/summer. Raptor abundance was higher during summer than winter, but did not differ between years. Thirteen of the 33 species recorded showed temporal changes in abundance, or are known to be migrants in the region. White-tailed Kite (Elanus leucurus), Yellow-headed Caracara (Milvago chimachima) and Southern Caracara (Caracara plancus) had higher abundance during fall/winter than spring/summer, which might be attributed to nomadic movements in agricultural landscapes. Changes in abundance of Savanna Hawk (Buteogallus meridionalis) and American Kestrel (Falco sparverius) suggest irruptive or nomadic movements. Turkey Vulture (Cathartes aura), Snail Kite (Rostrhamus sociabilis) and White-tailed Hawk (Geranoaetus albicaudatus) were more abundant in spring/summer than fall/winter, and our results suggest ...

Coyotes in the Crosswalks? Fuggedaboutit!

The article discusses the increasing adaptation of wildlife to urban environments. It is noted that a diverse range of species can been found in New York City, including white-tailed deer, red-tailed hawks, and beavers, attributing the change to pollution controls and increased green space. Particular focus is given to the growth of urban coyote populations in North America, which are found to have higher survival rates than those in rural areas.

Miscellaneous ecological notes on Brazilian birds of prey and owls

Sixteen opportunistic field observations of eight species of Brazilian raptors (Falconiformes and Strigiformes) are reported here as a contribution to the knowledge of the natural history of these poorly studied birds in Brazil. The observations are related to the food habits (Buteo albicaudatus, Herpetotheres cachinnans, Milvago chimachima, Falco femoralis), reproduction (Asio stygius, Megascops choliba), mobbing behaviour elicited in other birds (Geranospiza caerulescens, H. cachinnans, F. femoralis, A. stygius, Athene cunicularia) and a rare case of leucism in owls (A. cunicularia).

Comparison of the Breeding Biology of Sympatric Red-Tailed Hawks, White-Tailed Hawks, and Crested Caracaras in South Texas

Abstract We compared the breeding biology of sympatric nesting Red-tailed Hawks (Buteo jamaicensis), White-tailed Hawks (Buteo albicaudatus), and Crested Caracaras (Caracara cheriway) in south Texas during 2003 and 2004. We monitored 46 breeding attempts by Red-tailed Hawks, 56 by White-tailed Hawks, and 27 by Crested Caracaras. Observed nesting success was similar for Red-tailed Hawks (62%) and Crested Caracaras (61%), but lower for White-tailed Hawks (51%). Daily survival rates (0.99) were the same for all three species. Red-tailed Hawks and White-tailed Hawks both fledged 1.13 young per nesting pair and Crested Caracaras fledged 1.39 young per nesting pair. All three species nested earlier in 2004 than in 2003; in addition, the overall nesting density of these three species almost doubled from 2003 (1.45 pairs/km2) to 2004 (2.71 pairs/km2). Estimated productivity of all three species was within the ranges reported from other studies. Given extensive and progressive habitat alteration in some areas of s...

Habitat use of raptors in response to anthropogenic land use on Bonaire and Curaçao, Netherlands Antilles

We conducted fieldwork on Bonaire and Curaçao, Netherlands Antilles, to assess the distribution and abundance of resident diurnal raptors. In total, seventy-three 1 km2 sample plots were selected following a stratified random method and three landscape types were distinguished, i.e. cultivated area, hills and terrace. The diurnal raptors observed were the Crested Caracara Caracara plancus (93 records), White-tailed Hawk Buteo albicaudatus (37), and the American Kestrel Falco sparverius (44 on Curaçao only). In the hills and on the terraces, all species were more abundant on Curaçao than on Bonaire. Caracaras were found significantly more in hills compared to terraces or cultivated land on both islands, as did White-tailed Hawks on Curaçao. The American Kestrel made more use of cultivated area and least of hills. As detection of the raptors did not seem to differ between the landscapes and between the islands, we infer that the observed differences in distribution are a true reflection of their habitat use. Our results suggest that the ongoing urbanization on Curaçao and Bonaire may lead to a decline in the Caracara and the White-tailed Hawk. For the American Kestrel, cultivated areas — including urbanized parts — apparently provide the open area the birds need for hunting.

The Status of the White-Tailed Hawk in Arizona and Sonora, Mexico

ABSTRACT The white-tailed hawk (Buteo albicaudatus) formerly nested in the American Southwest but no longer appears to do so. We hypothesize that the reason for the absence of this always-scarce species in Arizona and Sonora, Mexico, is the elimination of its grassland habitat caused by cessation of grass fires in the tropic-subtropic regions of these two states. Loss of subtropical grasslands in the Southwest was due to livestock grazing removing fine fuels for grassland fires. When grassland prey sources became scarce due to the reduction in grass cover, nutritional levels were no longer sufficient to allow the white-tailed hawk to successfully engage in nest-building, egg-laying and the rearing of young. These conditions, initiated in the 1880s, have continued through to the present day in both southern Arizona and Sonora.

Feeding ecology of the White-tailed Hawk (Buteo albicaudatus) in south-eastern Brazil

The feeding ecology of the White-tailed Hawk (Buteo albicaudatus albicaudatus) was studied in southeastern Brazil. The aims of this study were to: (1) quantify the diet of the White-tailed Hawk, including the number of prey species eaten and their biomass; (2) investigate the influence of season on diet; and (3) describe the breadth of the diet. Pellets found beneath seven White-tailed Hawk nests and several roosting sites around the nesting sites were collected from September 2000 to September 2001. The analysis of 259 pellets revealed 31 prey species or morphospecies, 3296 individuals and 7.2 kg of estimated consumed biomass. Five insect orders (Hymenoptera, Heteroptera, Odonata, Isoptera and Lepidoptera) and one vertebrate order (Chiroptera) were reported as prey for the first time for this species. By number, invertebrates made up 88% of all prey items, 63% of which belonged to a single orthopteran family (Acrididae). Among vertebrates, rodents were the group most consumed by number and represented 73% of all vertebrate prey items. However, in terms of estimated biomass consumed, the most represented groups were rodents (50%), orthopterans (21%), birds (11%) and lizards (7%). Vertebrates alone yielded 77% of the total biomass consumed. Whereas the White-tailed Hawk may be classified as insectivorous by number of prey, it is carnivorous with respect to biomass ingestion. According to the Levin's diet-breadth index, this raptor could be considered to be a specialist predator of grasshoppers (Acrididae) by prey number and of rodents by prey biomass. Food eaten was dependent on season, with more mammals taken during the dry (breeding) season and a broader range of prey during the wet season.

NESTING HABITAT RELATIONSHIPS OF SYMPATRIC CRESTED CARACARAS, RED-TAILED HAWKS, ANDWHITE-TAILED HAWKS IN SOUTH TEXAS

We quantified nesting-site habitats for sympatric White-tailed Hawks (Buteo albicaudatus) (n = 40), Red-tailed Hawks (B. jamaicensis) (n = 39), and Crested Caracaras (Caracara cheriway) (n = 24) in the Coastal Sand Plain of south Texas. White-tailed Hawks and Crested Caracara nest sites occurred in savannas, whereas Red-tailed Hawk nest sites occurred in woodlands on the edge of savannas. White-tailed Hawk nest sites were in shrubs and trees that were shorter (3.5 ± 1.0 m) and had smaller canopy diameters (5.5 ± 2.1 m) than those of Red-tailed Hawks (10.1 ± 2.0 m, 13.7 ± 5.8 m) and Crested Caracaras (5.6 ± 1.7 m, 8.5 ± 3.5 m). Red-tailed Hawk nest sites had higher woody densities (15.7 ± 9.6 plants) and more woody cover (84 ± 19%) than those of White-tailed Hawks (5.6 ± 5.8 plants, 20 ± 21%) and Crested Caracaras (9.9 ± 6.7 plants, 55 ± 34%). Crested Caracara nest sites were in dense, multi-branched shrubs composed of more living material (97 ± 3%) than those of White-tailed (88 ± 18%) and Red-tailed hawks (88 ± 18%). Nest sites of White-tailed Hawks, Red-tailed Hawks, and Crested Caracaras were similar to random samples from the surrounding habitat indicating that preferred nesting habitat was available for each of these species at least within 60 m of active nest sites. Nest tree height, along with woody plant and native grass cover best discriminated nest sites among the three raptor species. There was no overlap at Red-tailed and White-tailed hawk nest sites in vegetation structure, while Crested Caracara nests were in habitat intermediate between the two other species. Partitioning of nesting habitat may be how these raptor species co-exist at the broader landscape scale of our study area in the Coastal Sand Plain of Texas.

SMALL MAMMAL SELECTION BY THE WHITE-TAILED HAWK IN SOUTHEASTERN BRAZIL

Abstract We analyzed diet and prey selection of the relatively unknown albicaudatus subspecies of the White-tailed Hawk (Buteo albicaudatus). Our study was based on an analysis of 259 pellets collected from September 2000 to September 2001 in the municipality of Juiz de Fora in southeastern Brazil. We also assessed the abundance of small mammals with pitfall traps (2,160 trap-nights). Small mammals composed 52.5% of the estimated biomass consumed by the hawks, and selection appeared to be mediated by abundance. The Bonferroni confidence intervals procedure revealed that when abundance of small mammals was higher, the hawks were selective, preying on Calomys tener more than would be expected by chance (P < 0.05); other rodents were consumed less than expected. Oligoryzomys nigripes, Oxymycterus sp., and Gracilinanus spp. were taken in the same proportion as they were found in the field. During reduced prey abundance (October–March), White-tailed Hawks preyed opportunistically on small mammals. Differences ...

Individual and Intersexual Variation in Alarm Calls of the White-Tailed Hawk

Although variation in bird vocalizations is well-studied (Marler 1960, Beer 1970, Jellis 1977, Falls 1982, Brown and Farabaugh 1991), few falconiforms have been intensively examined. The White-tailed Hawk (Buteo albicaudatus), however, exhibits remarkable patterns of intersexual as well as individual variation (Farquhar 1986) not previously identified in this species (Brandt in Bent 1937, Stevenson and Meitzen 1946, Slud 1964, Snyder and Snyder 1991). Hereafter referred to as alarm calls in White-tailed Hawks, these loud vocalizations are given in the context of potential danger such as when their territory has been intruded by mate or food competitors, nest predators, or humans. In Falconiformes, alarm calls (also known as territorial calls) gen-

Notes on Nesting Raptors in the Llanos of Venezuela

Observations on 13 species of hawks and owls in savanna-forest habitat of Venezuela suggest that at least some species breed principally in either the dry season or the wet season but usually not both. Nesting sites varied from stick nests in palms and trees to tree cavities; most species laid one to two eggs per clutch. Young White-tailed Hawks and Great Black Hawks appear to receive prolonged post-fledging care.

Predation by a White-Tailed Hawk and a Harris Hawk on a Wild Turkey Poult

On 6 May 1970, I observed a White-tailed Hawk (Buteo albicaudatus) and a Harris Hawk (Parabuteo unicinctus) attack and kill a six-day-old wild Turkey poult (Meleagris gallopavo intermedia). The incident occurred at 11:35 CDT on King Ranch, Inc., Kleberg County, Texas. The events prior to and after the incident are as follows. While observing a Turkey hen with poults, I noticed a White-tailed Hawk diving for the ground. It spread its wings and extended its feet just before landing on the Turkey poult. Two or three seconds after the White-tailed Hawk hit the poult, a Harris Hawk also landed on the poult. The hawks were facing each other on the ground with their feet grasping the young bird. The Turkey hen left her hiding place, some 25 m away, and flew directly toward the two hawks. As she approached, the hawks released the poult and took to the air with the Turkey hen in close pursuit. After chasing the hawks for some 20 m and flying to a height of approximately 45 m, at one time almost straight up, the hen glided to the ground and promptly returned to her previous hiding place. I believe this incident is of scientific interest for the following reasons: (1) it increases our knowledge of the White-tailed Hawk, a relatively unstudied species; (2) it illustrates an instance of direct competition between two species of raptors; and (3) it adds to the knowledge of predation on very young wild Turkeys.

Three Additional Specimens of the Eared Poor-Will from the State of Guerrero, México

Journal Article Predation by a White-Tailed Hawk and a Harris Hawk on a Wild Turkey Poult Get access Harry H. Haucke Harry H. Haucke Caesar Kleberg Research Program in Wildlife Ecology Texas A & M University College Station, Texas 77843 Search for other works by this author on: Oxford Academic Google Scholar The Condor, Volume 73, Issue 4, 1 October 1971, Page 475, https://doi.org/10.2307/1366673 Published: 01 October 1971 Article history Accepted: 01 December 1970 Published: 01 October 1971

The Relationship of Grazing Cattle to Foraging Rates in Anis

MANY species of birds regularly forage on organisms that have been flushed by a source other than the birds themselves. This source may be nonliving; Stevenson and Meitzen (1946) report White-tailed Hawks (Buteo albicaudatus) coming from as far as 10 miles to follow grass fires in Texas. Similarly, raptors often follow trains to feed on animals they flush; see, for example, Kenyon's (1942) work on Pigeon Hawks (Falco columbarius). More commonly, the source is living. A large complex of neotropical birds depends for their food upon arthropods flushed by swarms of army ants (Willis, 1967, 1968). Certain old world hornbills, drongos, and leafbirds follow troops of monkeys to obtain the insects they disturb (Chapin, 1939; Stott, 1947). Many of these feeding associations involve large ungulates. The Brown-headed Cowbird (Molothrus ater) originally fed in close association with bison; in modern times this association has shifted to cattle. Many species of herons also feed with cattle; probably the best known of these is the Cattle Egret (Bubulcus ibis). Finally two tropical American cuckoos, the Groove-billed Ani (Crotophaga sulcirostris) and the Smooth-billed Ani (Crotophaga ani), regularly forage with domestic cattle wherever cattle have been introduced into their normal range. Heatwole (1965) showed that Cattle Egrets in Puerto Rico are benefited in both time and energy by their association with cattle. Rand (1953) showed that the association between Groove-billed Anis and cattle in El Salvador was correlated with a greater feeding rate by the anis at any time of year, but the benefit was greater in the dry season than in the wet season. Very little other work has been done to determine the amount of benefit the foraging birds gain by this practice. The present study was conducted from this point of view on both species of ani in Costa Rica during the wet season of 1969. Each species of ani was watched both foraging with cattle and foraging alone to determine whether or not these birds derive any measurable benefit from their association with cattle. The foraging habits of the two ani species, as described in detail by Bent (1940), are remarkably similar: both regularly forage in small groups of 6 to 10 birds; both are ground feeders; and both are primarily insectivorous, grasshoppers and other orthopterans making up large proportions of the diet of each. Anis of both species, when foraging with grazing cattle, stay very close to the head or front legs of the

North American Migrants in the State of Veracruz, Mexico: A Summary

PRIOR to the appearance of a comprehensive report, now in preparation, on the more than 700 forms of birds known from Veracruz, it seems desirable to summarize the present status there of migrants from the north. It is hoped that this summary may prove useful to students of North American and Mexican birds, and at the same time by revealing gaps in our knowledge of migratory birds in Veracruz, that it may stimulate further work in this interesting, readily accessible, region. Scope.-Essentially, this paper is limited to birds of the A.O.U. Check-List (4th ed., 1931, and nineteenth through twenty-eighth supplements) which have been found in Veracruz but are not known to breed there. All but two, Wilson's Petrel (Oceanites oceanicus) and the Black-headed Gull (Larus ridibundus), nest in North America. For completeness, I have included the following migratory forms whose breeding status in Veracruz remains to be determined: Eastern Least Bittern (Ixobrychus exilis exilis), Florida Common Gallinule (Gallinula chloropus cachinnans), Wilson's Thick-billed Plover (Charadrius wilsonia wilsonia), Northern Black Skimmer (Rynchops nigra nigra), and American Barn Swallow (Hirundo rustica erythrogaster). Certain other species, for example the Rough-winged Swallow (Stelgidopteryx ruficollis), have one or more migratory northern races and another form nesting in Veracruz. In such cases, I have listed the northern race(s) when represented by critically determined Veracruz specimens. Among the migratory or partially migratory North American forms omitted from this summary for the reason that their breeding in Veracruz is established or quite probable are the Pied-billed Grebe (Podilymbus podiceps subspecies?), Eastern Green Heron (Butorides virescens virescens), Black-crowned Night Heron (Nycticorax nycticorax hoactli), Yellow-crowned Night Heron (Nyctanassa violacea violacea), Masked Duck (Oxyura dominica), White-tailed Hawk (Buteo albicaudatus hypospodius), American Coot (Fulica americana americana), Black-necked Stilt (Himantopus mexicanus), Western Burrowing Owl (Speotyto cunicularia hypugaea), and Eastern Varied Bunting (Passerina versicolor versicolor). I have tried to indicate each bird's relative abundance in Veracruz, and, where sufficient data exist, its altitudinal preference and season(s)