Puna Hawk
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The variable hawk (''Geranoaetus polyosoma'') is a polymorphic species of
bird of prey Birds of prey or predatory birds, also known as (although not the same as) raptors, are hypercarnivorous bird species that actively predation, hunt and feed on other vertebrates (mainly mammals, reptiles and smaller birds). In addition to speed ...
in the family
Accipitridae The Accipitridae () is one of the four families within the order Accipitriformes, and is a family of small to large birds of prey with strongly hooked bills and variable morphology based on diet. They feed on a range of prey items from insects ...
. It is widespread and often common in open habitats in western and southern South America, including the
Falkland Islands The Falkland Islands (; ), commonly referred to as The Falklands, is an archipelago in the South Atlantic Ocean on the Patagonian Shelf. The principal islands are about east of South America's southern Patagonian coast and from Cape Dub ...
. Its
taxonomy image:Hierarchical clustering diagram.png, 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme o ...
is disputed, with some splitting it into the widespread red-backed hawk (''G. polyosoma'') and the Puna hawk or Gurney's hawk (''G. poecilochrous'') of the central and north
Andean The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long and wide (widest between 18°S ...
highlands, but the differences between the two are unclear. Most recent authorities have supported the lumping together of the two hawks although the issue still is controversial.South American Classification Committee (2007).
Merge Buteo poecilochrous into B. polyosoma.
'. Accessed 10-07-2009
South American Classification Committee (2009).

'. Accessed 10-07-2009
On the contrary, the rare
taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...
from the
Juan Fernández Islands The Juan Fernández Islands () are a sparsely inhabited series of islands in the South Pacific Ocean, reliant on tourism and fishing. Situated off the coast of Chile, they are composed of three main volcanic islands: Robinson Crusoe Island, R ...
is relatively distinctive, and possibly worthy of species recognition as the Juan Fernández hawk (''B. exsul'').Jaramillo, A. Burke, P., & Beadle, D. (2003). Birds of Chile. Christopher Helm. In this article and most current accounts, the three races are regarded as subspecies.


Description

The name variable hawk is fully deserved, as both sexes occur in several morphs. Adults of all have a white tail with a contrasting black subterminal band and grey wings barred dark (in flight from below, the
remiges Flight feathers (''Pennae volatus'') are the long, stiff, asymmetrically shaped, but symmetrically paired pennaceous feathers on the wings or tail of a bird; those on the wings are called remiges (), singular remex (), while those on the ta ...
appear whitish with fine barring and a broad black tip). The remaining
plumage Plumage () is a layer of feathers that covers a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage differ between species and subspecies and may vary with age classes. Within species, there can b ...
varies from very dark grey to whitish, and some individuals have reddish-brown to the underparts. Females usually have a reddish-brown back, which males usually lack, although at least some males also have this. The taxon ''exsul'' from the Juan Fernández Islands is far less variable, being whitish below and grey above in adults of both sexes. At least 27 distinct adult plumages are known in this species, possibly the most of any
raptor Raptor(s) or RAPTOR may refer to: Animals The word "raptor" refers to several groups of avian and non-avian dinosaurs which primarily capture and subdue/kill prey with their talons. * Raptor (bird) or bird of prey, a bird that primarily hunt ...
(although the widespread
red-tailed hawk The red-tailed hawk (''Buteo jamaicensis'') is a bird of prey that breeds throughout most of North America, from the interior of Alaska and northern Canada to as far south as Panama and the West Indies. It is one of the most common members of ...
& Eurasian buzzard have also been noted for a widespread but more uniform spectrum of plumage variations) with no relationship to
morphometric Morphometrics (from Greek μορΦή ''morphe'', "shape, form", and -μετρία ''metria'', "measurement") or morphometry refers to the quantitative analysis of ''form'', a concept that encompasses size and shape. Morphometric analyses are co ...
variables and only minor geographic variation.


Size

Size is also variable in this confusing species. Lengths can range from 45 to 62 cm (18–25 in) and wingspans from 113 to 151 cm (45–60 in). Weights can range from 800 to at least 1,800 grams (1.8-4 lbs). The Puna hawk subspecies is generally considered to be at the larger end of the size spectrum and the red-backed hawk at the smaller (Juan Hernandez hawk being intermediate), but these distinctions are difficult at best in the field. Overall, however, this species rates as a large ''Buteo''.


Habitat

Variable hawks occupy open habitats at all elevations. The red-backed race inhabits the widest range of areas of the variable hawk races, including above
tree line The tree line is the edge of a habitat at which trees are capable of growing and beyond which they are not. It is found at high elevations and high latitudes. Beyond the tree line, trees cannot tolerate the environmental conditions (usually low ...
in mountains, Pacific coastal foothills, Patagonian
steppe In physical geography, a steppe () is an ecoregion characterized by grassland plains without closed forests except near rivers and lakes. Steppe biomes may include: * the montane grasslands and shrublands biome * the tropical and subtropica ...
s,
agricultural Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created f ...
areas and edges of river galleries,
beech Beech (genus ''Fagus'') is a genus of deciduous trees in the family Fagaceae, native to subtropical (accessory forest element) and temperate (as dominant element of Mesophyte, mesophytic forests) Eurasia and North America. There are 14 accepted ...
woods and humid premontane and lowland forests. Though often the most likely race to be found in lowlands, even the red-backed is less than common below an elevation of 500 m (up to 3,000 m). The Juan Fernandez race is found on the islands' volcanic slopes and barren grazed grasslands at all elevations. The Puna race are often a common element above
tree line The tree line is the edge of a habitat at which trees are capable of growing and beyond which they are not. It is found at high elevations and high latitudes. Beyond the tree line, trees cannot tolerate the environmental conditions (usually low ...
in
páramo Páramo () may refer to a variety of alpine tundra ecosystems located in the Andes Mountain Range, South America. Some ecologists describe the páramo broadly as "all high, tropical, montane vegetation above the continuous timberline". A narrower ...
and puna habitat, at higher elevations (5,000+ m) than almost any other raptor. Smaller numbers of the latter race may visit mountain scrub and stunted ''
Polylepis ''Polylepis'' is a genus comprising 28 recognised shrub and tree species, that are endemic to the mid- and high-elevation regions of the tropical Andes, up to above sea level. It is distributed from Venezuela to Patagonia. In Peru, plants in the ...
'' woodland at as low 900 m (but rarely below 2,900 m).


Behavior

They are most often seen soaring on warm thermals but may be seen on almost any type of raised perch (from sign posts to large trees). They prey on almost any small to medium-sized animals that can be caught, but smallish mammals comprise more than 90% of prey in some studies. The most commonly recorded prey includes
cavies Caviidae, the cavy family, is composed of rodents native to South America and includes the domestic guinea pig, wild cavies, and the largest living rodent, the capybara. They are found across South America in open areas from moist savanna to th ...
,
tuco-tuco A tuco-tuco is a neotropical rodent in the family Ctenomyidae. Tuco-tucos belong to the only living genus of the family Ctenomyidae, ''Ctenomys'', but they include approximately 60 different species. The common name, "tuco-tuco", comes from the " ...
s,
rabbit Rabbits are small mammals in the family Leporidae (which also includes the hares), which is in the order Lagomorpha (which also includes pikas). They are familiar throughout the world as a small herbivore, a prey animal, a domesticated ...
s,
mice A mouse (: mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...
and páramo rats.
Earthworm An earthworm is a soil-dwelling terrestrial invertebrate that belongs to the phylum Annelida. The term is the common name for the largest members of the class (or subclass, depending on the author) Oligochaeta. In classical systems, they we ...
s,
weevil Weevils are beetles belonging to the superfamily Curculionoidea, known for their elongated snouts. They are usually small – less than in length – and herbivorous. Approximately 97,000 species of weevils are known. They belong to several fa ...
s,
orthopteran Orthoptera () is an order of insects that comprises the grasshoppers, locusts, and crickets, including closely related insects, such as the bush crickets or katydids and wētā. The order is subdivided into two suborders: Caelifera – grasshopp ...
s and other
invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...
s are often taken. Birds are sometimes taken, including tired
petrel Petrels are tube-nosed seabirds in the phylogenetic order Procellariiformes. Description Petrels are a monophyletic group of marine seabirds, sharing a characteristic of a nostril arrangement that results in the name "tubenoses". Petrels enco ...
s around
Juan Fernández Islands The Juan Fernández Islands () are a sparsely inhabited series of islands in the South Pacific Ocean, reliant on tourism and fishing. Situated off the coast of Chile, they are composed of three main volcanic islands: Robinson Crusoe Island, R ...
. Other prey include other
rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...
s &
lagomorph The lagomorphs () are the members of the taxonomic order Lagomorpha, of which there are two living families: the Leporidae (rabbits and hares) and the Ochotonidae ( pikas). There are 110 recent species of lagomorph, of which 109 species in t ...
s,
frog A frog is any member of a diverse and largely semiaquatic group of short-bodied, tailless amphibian vertebrates composing the order (biology), order Anura (coming from the Ancient Greek , literally 'without tail'). Frog species with rough ski ...
s,
lizard Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...
s,
snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...
s, and
fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...
. The variable hawk hunts with prey being spotted while soaring from the air and pinned on the ground. Breeding is at various seasons and may be variable for all races. They build large stick nests on any elevated structure available, and sometimes breed cooperatively. One to three eggs are laid. The incubation period is 26 to 36 days. The nestlings fledge anywhere from 40 to 74 days. The larger-bodied, high-elevation hawks take longer to incubate and much longer to fledge than lower elevation hawks.


References

*"Raptors of the World" by Ferguson-Lees, Christie, Franklin, Mead & Burton. Houghton Mifflin (2001), . * * {{Taxonbar, from=Q1576679 variable hawk Birds of South America Birds of Chile Birds of Argentina Birds of Ecuador Birds of Peru Birds of Patagonia Birds of the Falkland Islands Páramo fauna variable hawk