Gray buzzard
| Gray buzzard | ||||||||||||
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Adult gray buzzard |
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| Scientific name | ||||||||||||
| Buteo plagiatus | ||||||||||||
| ( Schlegel , 1862) |
The gray buzzard ( Buteo plagiatus ) is a small to medium-sized, hawk-like buzzard, whose distribution area is mainly in Mexico and northern to central Central America . After many taxonomic revaluations and re-evaluations, as of the end of 2019 it will be placed in the genus Buzzard ( Buteo ), which in turn belongs to the hawk family (Accipitridae). The American common names are Gray Hawk and Mexican Goshawk. The latter reflects the resemblance of the gray buzzard to the goshawk ( Accipiter gentilis ).
The gender of the gray on the top and gray-white on the bottom gesperberten bird differ in color only imperceptibly, but the females are larger and not insignificantly heavier. He is an inhabitant of mostly river-accompanying woodlands, mainly the hill country and submontane altitude level . The gray buzzards feed mainly on reptiles , predominantly on lizards . In the greater part of its range, the species is resident , only some of the northernmost populations are short-range migrants .
The sister species of the gray buzzard is the two- banded buzzard ( Buteo nitidus ), the range of which, after a gap in Costa Rica that is uninhabited by both species, adjoins that of the gray buzzard and extends to northern Argentina . Buteo plagiatus was considered a subspecies of B. nitidus for a long time and was only recognized as an independent species in 2012 . The type epithet of the buzzard, first described by Hermann Schlegel in 1862 using a bellows from Veracruz as Asturina plagiata , relates to the banded chest and belly side (Latin plaga = stripes). According to the IUCN , the population of this monotypical species is not endangered (LC = Least Concern).
The vast majority of biological information relates to populations in the United States. Comparatively little is known about this species from the rest of the distribution area.
Appearance
Large females of the gray buzzard reach the size and weight of a small male hawk, which is similar in color and body shape to B. plagiatus . In the field, the upper side appears uniformly dark gray, the underside with intense black and white bands. Gray buzzards have short, broad, rounded wings and fly with a sequence of rapid wingbeats, which is followed by a gliding phase. When sliding, which often takes place relatively close to the ground, the wings are held horizontally and the control springs spread. The frequent twisting and twisting of the tail is noticeable.
Adult male gray buzzards weigh on average 429 grams, adult females 628 grams. The average size of the males is 41 centimeters, that of the females 44 centimeters. According to Bergmann's rule , the buzzards of the northernmost populations are the largest and heaviest.
Adult plumage
The upper side is indistinct and faded blackish banded on a uniformly dark gray background. On the head, which is also colored, the sparrow mark is often more indistinct or completely absent, so that it can appear a little lighter. In the sister species B. nitidus , the sparrows on the top and the head are much more accentuated. A dark stripe above the eye is almost always clearly visible. The entire underside is evenly and finely black and white longitudinally sparred. The bright yellow feet are feathered up to the intertarsal joint and, like the rest of the underside plumage, are finely pinned. The rump and the base of the tail on the underside are white; the control springs have a wide, deep black band on the upper side, which, in addition to the terminal band, usually also includes two somewhat narrower bands. On the underside, only the terminal strip is black, the other strips are medium gray. The under wing-coverts are slightly finer than the body plumage, as are the wings - but indistinctly and irregularly - whose inner lugs are light gray, creating a gray-white gradation. The last third of the five outer, not very long hand wings are dark gray, the other wings are slightly lighter. The iris is dark brown, the beak horn-colored and covered with a yellow wax skin at the base. Females are colored the same, but mostly a little darker.
Youth plumage
The juvenile plumage differs very clearly from the adult plumage; Above all, all gray color elements are missing and the characteristic sparrows are only formed on the feathered areas of the legs.
The top is matt dark brown. Most back, mantle and flank feathers have a lighter edge, creating a speckled, piebald impression. The head and neck are clearly streaked and spotted with a matt dark brown color on a yellowish-white background. A light stripe over the eyes and creamy beige cheeks are striking . The underside is on a creamy white or yellowish background, mostly over a large area, darkly dashed and spotted in longitudinal lines. The control springs are slightly longer than those of adults. They are matt brown on the upper side and have indistinct dark banding, on the underside they are cream-brown and clearly several times darker banded, with the terminal band being the darkest and widest. The under wing-coverts are darkly spotted and noticeably darker than the wings, whose bright inner plumes they clearly brighten. The color of the featherless parts of the body largely corresponds to that of the adult plumage.
While adult gray buzzards are almost unmistakable, juvenile strongly juvenile broad-winged buzzards and juvenile red-shouldered buzzards are similar .
Mauser
When hatching, the chicks have whitish-gray downy plumage that gradually fades. The first control springs break after about 10 days , followed by the hand swing . By the 20th day, all body feathers are molten , only the head is still covered . When they fly out, the young birds have largely molted into their juvenile plumage, but the control feathers and some wings have not yet reached their final length. Young gray buzzards carry this youthful plumage until next spring. Between April and August, young gray buzzards switch to adult plumage.
Vocalizations
Gray buzzards are acoustically active all year round, but they are only acoustically noticeable in the pre-breeding season. The most frequent call during this period is a long drawn-out whistle that begins explosively and rises and then ends slightly nasally at a falling pitch. As the excitement increases, the second half of the call takes on a neighing character. This call serves to delimit the territory, as a partnership contact call and as an alarm call. During the breeding season, a sequence of calls can often be heard in the vicinity of the nest, which consists of different numbers of quickly arranged elements. It mainly serves the communication between the partners and the area delimitation. These main calls are often combined and adapted to the situation. Both sexes call; the female's pitch is lower and the voice characteristics less sharp.
distribution
Breeding area
The gray buzzard is a breeding bird of the southernmost USA with about 100 breeding pairs. The main deposits are in Arizona between the river systems of the San Pedro and Santa Cruz , both left tributaries of the Gila River . Further, smaller breeding occurrences exist on the lower Rio Grande and other places in Texas and sporadically in New Mexico . In Mexico, the coastal areas and the adjoining hinterland are populated both on the Pacific coast and on the coast of the Gulf of Mexico approximately up to the level of Tehuacán , where the eastern and western breeding areas meet. Further south-east, Mexico is extensively populated in suitable habitats and then also the Central American states as far as central Costa Rica. The breeding area of the gray buzzard ends in the province of San José . After a gap of about 50 km width, the breeding area of the closely related two-banded buzzard , which until recently was regarded as conspecific , follows, which extends over large parts of northern and central South America to northern Argentina.
habitat
Vertically, the gray buzzard is particularly widespread at heights between sea level and around 800 meters above sea level . In particularly suitable habitats, it can also be found as a breeding bird at heights of up to 1400 meters. Most of the breeding sites show a certain preference for water, but can even be located on the edge of arid zones.
In the USA, it breeds mainly in woody trees that accompany rivers , which in turn are connected to mequite populations , and in canyons with corresponding bush and tree vegetation. In addition to various types of hackberry trees , willows , ash trees and American plane trees are important components of suitable tree vegetation. However, marginal areas of tropical forest areas, loose oak and pine forests, palm groves, even thorn steppes are populated, provided that watercourses are nearby and lizards are available in sufficient numbers as the main prey. Further to the south-east, the species also breeds in savannahs that are criss-crossed by rivers and covered with islets of wood or individual trees .
Space requirements
The species' footprint is possibly the smallest of any buzzards living in North America. In Arizona district sizes between 59.2 and 90.3 hectares were surveyed. This comparatively small area is vigorously defended against conspecifics, regardless of whether it is juvenile or adult gray buzzards. The smallest nest distance to a nest of a conspecific was 1.18 kilometers, to a nest of another bird of prey ( round-tailed cattle ) only 50 meters. This noticeable tolerance of other birds of prey within the area, even in the immediate vicinity of the nest, can be explained by the high food specialization of B. plagiatus . It is not known whether the territories will remain upright in the winter months and what the size and type of territoriality outside the USA are.
migration
Some populations in the southern United States and northern Mexico are short-range migrants. The boundary between migrating and resident populations is between 28 ° and 29 ° north. Gray buzzards leave the breeding area late, not until late September / early October. Most of them return at the end of February at the earliest, but especially in March.
Food and subsistence
In the well-studied breeding populations of the southern USA, the gray buzzard feeds primarily on reptiles, with lizards being the main prey animals and making up the majority of the ingested biomass. Up to 79% of the prey animals are reptiles; small mammals make up 11% and birds 10% of the animals captured. Amphibians and large insects are regularly eaten and also fed to the chicks, but they do not play a role in terms of number or in terms of the ingested biomass.
Outside of the United States, diet preferences for the species are likely to be similar or the same, but the species composition is unknown.
Among the lizards, genera from the Phrynosomatidae family dominate , mainly spiny guans , as well as various species of rail lizards . More rarely, but regularly, the gray buzzards prey on snakes , often the common coachman whip snake and various garter snakes . Small rodents ( American bush rats , white-footed mice ) are the most common mammals, but occasionally B. plagiatus also beats animals up to the size of a cottontail rabbit .
Small and medium-sized songbirds, mainly New World chambers and some species from the family Tyrannidae , especially the tyrant almost in the entire distribution area , form the main mass of the captured birds; the most representative among them are the Gambel's quail and various species of pigeons, such as the white-winged dove and mourning dove .
Preferred hunting grounds are mesquite populations and other light forest areas with little undergrowth, as well as adjacent open areas. The gray buzzards are primarily hunters who observe the surroundings from an elevated position and strike a prey they spotted on the ground after a short glide flight. Occasionally he reads tree-dwelling lizards from the trunk or branches as they fly by. When the prey is carried to the nest, the head is often removed beforehand. If the first attack is unsuccessful, there will be no further pursuit. The seats are changed frequently. The gray buzzard usually catches birds in flight or surprises them in the nest. In addition to high-seat hunting, low, systematic search flight hunting is an often used hunting strategy. You can also often see the gray buzzards hunt for fleeing reptiles and mammals along the edges of the fire.
Breeding biology
Pair formation and courtship
When the first brood, the gray buzzards are fully moulted into adult plumage, i.e. at least two years old. Females are often expected to breed for the first time at this age, but the majority of males only in their third year of life. The pair bond is monogamous and often lasts into the winter months during the breeding season, so that last year's breeding partners often mate again in the following year. The species breeds once a year, replacement broods were found when the clutch was lost very early.
The pairs form in the United States and northern Mexico in early spring, usually between late March and early April; in central and southern Mexico up to a month earlier. In Costa Rica nest building was already detected at the end of December. Nest building begins very soon after arrival in the breeding area or at the same time as it is set up and is an essential part of pair bonding.
The courtship ritual corresponds to that of other buzzards. Essentially, it consists of common sightseeing or sightseeing tours of the male, during which the female is present. These expressive flights often take place just above the canopy and also serve to delimit the territory. Sometimes, however, the partners rise higher and fly with strongly accentuated wing beats, jiggle and fall steeply, only to gain altitude again afterwards; sometimes the male knocks down on the lower flying female, which only moves to the side just before touching it; Occasionally the partners also clasp each other with their claws and tumble spiraling down almost to the treetops before they loosen again. Frequent series of shouts accompany these courtship rituals. During this time, the buzzards often copulate, usually alongside on a strong branch and sit and rest in close proximity, but without physical contact.
Nest location and nest
In the USA and northern Mexico, the majority of nests are built in woody trees along the river, especially on different poplars and willows, as well as in walnut trees Juglans major , in various ash species, and occasionally in oaks . Mesquite populations, which were described as the most common nest carriers in older literature, are currently selected less often. Further south, too, poplars and walnut trees predominate, and to an increasing extent in central and southern Mexico and Central America, Mexican bald cypresses , various oak species and pines . The nest is 6 - 32 meters high, well hidden, mostly in the fork of a strong branch.
The nest is built by both partners. The male brings most of the material, the female does most of the work on the very compact and stable construction. Above all, green twigs, which the male breaks off from outer branches, are used. The nest cavity is lined with several layers of leaves, which are also renewed during the brood and the nestling period. With an average size of 51 centimeters in diameter and 26 centimeters in height, the nest is relatively small, and with a bowl depth of only a few centimeters, it is very shallow. The nests are often used twice, less often three times.
Clutch and nestling time
Laying begins in Central America mostly in February, in southern Mexico in March. The Central Mexican gray buzzards begin to lay eggs in early April, the northern Mexican and southern US buzzards begin to lay eggs in late April and early May. The clutches of the gray buzzard comprise 2–3 (1–4) mostly unmarked, matt white or bluish white eggs with an average size of 50.4 × 40.3 millimeters. The clutch size seems to increase with latitude, in Arizona it averaged 2.6 eggs. Nothing is known about the laying distance and the start of breeding. It only breeds the female.
When hatching, the chicks are covered with gray-white dunes . The wings and control springs break through after about 12 days, during which time the first body and cover springs are visible. At 20 days there are only remains of the chick down on the head. Gray buzzards finally leave the nest from the 42nd day after they had often been in the branches in the immediate vicinity of the nest a few days earlier. By this time, the wings and control springs have approached, but not always, their final length, and the young are the weight of adult individuals.
During the breeding season and in the first two to three weeks of the nestling season, the male alone cares for the female and later for the females and chicks. When the young are largely able to cut up prey, both parents bring food; the young then often stay alone for a long time and are only huddled in bad weather or shaded when the sun is too intense.
Dismigration, Breeding Success, and Life Expectancy
All available studies on these parameters only include small samples and come from the US breeding areas.
After a guided tour with an unknown average duration, the young birds leave the immediate vicinity of the nest, but do not move too far from the place of birth. The gray buzzard seems to be very faithful to the breeding site. When they reach sexual maturity, young birds try to establish their own breeding territory in the wider vicinity of their place of growth. Two buzzards ringed when they were young were found after 5 years as breeding birds 13.6 km and 59 km respectively
Breeding success and departure rate seem to be low. Between 1995 and 1997, 27 nesting sites were closely monitored in Arizona. In these 3 years 33% of the breeding pairs brought at least one young to fly each year and 26% were successful twice or once. 15% of the broods failed each year. This study found 1.32 cubs as the average annual number of reproductions.
There is no information about the average life expectancy.
Systematics
In 1854 Martin Hinrich Carl Lichtenstein recorded two specimens with the binomial Buteo plagiatus in his catalog of the birds contained in the zoological collection of the Royal University of Berlin ; he roughly states Mexico as origin. He also catalogs 5 bellows of Asturina nitida from Brazil and Cayenne . B. plagiatus was clearly separated from A. nitida by Lichtenstein . It is not known whether the taxonomic assignment stems from Lichtenstein himself or was already in use before. In a detailed note on Asturina nitida , Hermann Schlegel describes these two bellows under the name Asturina plagiata in 1862 ; he goes into the differences to A. nitida , but does not explain the switch from Buteo to Asturina . He gives Vera Cruz as the place where the bellows are collected . It also clearly distinguishes between A. plagiata and A. nitida . Schlegel is the first to describe the species.
As a result, on the one hand the allocation of the gray buzzard between the genera Asturina and Buteo changes several times, on the other hand the view as to whether Asturina / Buteo plagiata / us should be considered as a species or a subspecies. Although the most authoritative authorities continued to regard the gray buzzard as a subspecies, the differences between plagiatus and nitidus were often pointed out, and the striking distribution gap in Costa Rica was mentioned.
The consequences of the first extensive molecular genetic investigation were, among other things, that the genus Asturina was dissolved and all species that had previously belonged to Asturina were placed in Buteo . However, Buteo n. Plagiatus was still considered a subspecies of B. nitidus . It was not until the work of Brian A. Millsap et al ., In which the authors pointed out the color differences and differences in the vocal repertoire, that the two species were separated and the currently valid taxonomic relationships were established.
Buteo plagiatus is monotypical. B. nitidus is considered a sister species. Buteo ridgwayi and Buteo lineatus are closely related.
Persistence and Threat
Studies on population and population development are only available from the US American part of the distribution area. The main occurrences are in Arizona with about 80 breeding pairs; 10-20 pairs breed in Texas and a few in New Mexico. These brood populations are stable or even increasing slightly.
Outside of this range the species is sometimes described as not rare , but elsewhere as rare . Reliable quantitative assessments are not possible. Likewise, no specific causes of danger can currently be identified. Accordingly, the IUCN assesses the inventory situation as least concern .
literature
- BD Bibles, RL Glinski, and RR Johnson: Gray Hawk (Buteo plagiatus) . Version 2.0. (2019) In: AF Poole and FB Gill (Eds.) The Birds of North America . Cornell Lab of Ornithology, Ithaca, NY, USA. 2019 https://doi.org/10.2173/bna.652
- J. del Hoyo, N. Collar, and JS Marks: Gray Hawk (Buteo plagiatus) . In: J. del Hoyo, A. Elliott, J. Sargatal, DAChristie, DA and E. de Juana (eds.): Handbook of the Birds of the World Alive . Lynx Edicions, Barcelona 2019 (downloaded from https://www.hbw.com/node/467355 on November 19, 2019).
- James Ferguson-Lees , David A. Christie : Raptors of the World . Houghton Mifflin, Boston 2001, ISBN 0-618-12762-3 .
- Gary Stiles and Alexander Skutch: A Guide to the Birds of Costa Rica. Comstock Publishing Associate, Ithaka (NY) 1989; ISBN 978-0-8014-9600-4
Web links
Individual evidence
- ↑ a b c d e f g h i J. del Hoyo, N. Collar and JS Marks: Gray Hawk (Buteo plagiatus) . In: J. del Hoyo, A. Elliott, J. Sargatal, DA Christie, DA and E. de Juana (eds.): Handbook of the Birds of the World Alive . Lynx Edicions, Barcelona 2019 (downloaded from https://www.hbw.com/node/467355 on November 19, 2019).
- ^ R. Terry Chesser: Fifty-Third Supplement to the American Ornithologists Union Check-List of North American Birds . In: The Auk. Volume 129, 3rd edition 2012 doi: 10.1525 / auk.2012.129.3.573 (PDF, engl.)
- ↑ James A. Jobling: The Helm Dictionary of scientific Bird Names . Christopher Helm, London 2010. ISBN 978-1-4081-2501-4 p. 309
- ↑ a b Buteo plagiatus in the IUCN 2016-3 Red List of Threatened Species . Listed by: BirdLife International, 2016. Retrieved November 19, 2019.
- ↑ a b c d e f g h i j k l m n o p q r s B. D. Bibles, RL Glinski, and RR Johnson: Gray Hawk (Buteo plagiatus) . Version 2.0. (2019) In: AF Poole and FB Gill (Eds.) The Birds of North America . Cornell Lab of Ornithology, Ithaca, NY, USA. 2019 https://doi.org/10.2173/bna.652
- ↑ a b c d e James Ferguson-Lees, David A. Christie: Raptors of the World . Houghton Mifflin, Boston 2001, ISBN 0-618-12762-3 . P. 647
- ↑ a b James Ferguson-Lees, David A. Christie: Raptors of the World . Houghton Mifflin, Boston 2001, ISBN 0-618-12762-3 . Pp. 208-209 and 647
- ↑ Voice example: Revierruf
- ↑ Voice example: series of calls
- ^ Gary Stiles and Alexander Skutch: A Guide to the Birds of Costa Rica. Comstock Publishing Associate, Ithaka (NY) 1989; ISBN 978-0-8014-9600-4 p. 107
- ^ Nomenclator Avium Musei Zoologici Berolinensis. Berlin 1854 Biodiversity Heritage Library
- ^ Hermann Schlegel: Revue méthodique et critique des collections déposées dans cet établissement . Leyden, Rijksmuseum van Natuurlijke Historie 1862. Biodiversity Heritage Library
- ↑ Martin J. Riesing, Luise Kruckenhauser, Anita Gamauf (†) and Elisabeth Haring: Molecular phylogeny of the genus Buteo (Aves: Accipitridae) based on mitochondrial marker sequences . In: Molecular Phylogenetics and Evolution 27 (2003) pp. 328-342. doi: 10.1016 / S1055-7903 (02) 00450-5 Kruckenhauser & Gamauf et al.
- ^ Brian A. Millsap, Sergio H. Seipke and William S. Clark: The Gray Hawk (Buteo nitidus) is Two Species . In: The Condor, Volume 113, Issue 2, May 1, 2011, pages 326-339. doi: 10.1525 / cond.2011.100089 (PDF)