Buteo galapagoensisGalapagos hawk

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Geographic Range

Galapagos Hawks Buteo galapagoensis are indigenous to a group of islands called the Galapagos Islands. The islands are located 600 miles west of Peru and Ecuador and just south of the equator, covering a 200 square mile range. Currently, this species can be found on the islands of Charles, Chatham, Duncan and Indefatigable. Previously, they were also found on Baltra and Tower islands (Thornton 1971).

Habitat

This bird can be found throughout all the geographical biomes on the Galapagos Islands. These regions include the shoreline, lava fields, deciduous forest and mountaintops (Thornton 1971, del Hoyo, J., et al. 1994).

Physical Description

Galapagos Hawks are similar in size and shape to the Red-Tailed Hawk Buteo jamaicensis and the Swainson's Hawk Buteo swainsoni of North America. The hawks are about 55 cm (21.5 in) long and have a wingspan of 120 cm (47 in). The iris of the eye is brown, and the legs, cere and the soft skin at the base of the beak are yellow. The tail is buffy white with lightly barred tail feathers. Females are noticeably larger than the males (sexually dimorphic). Unlike the adults, juvenile hawks are spotted with dark brown specks and pale breasted. Like other members of the Buteo species, these hawks have superior eyesight (Thornton 1971, del Hoyo, J., et al.1994, Wheeler, et al. 1995).

Reproduction

The Galapagos Islands are tropical and do not have seasons; therefore, the breeding patterns of the Galapagos Hawk tend to revolve around the island's local weather conditions as opposed to its seasons. The nest is quite large ranging from 80-100 cm (31- 39 in) wide and up to three meters (10 ft) tall. The female will lay one to three eggs and the incubation period lasts for 37-38 days. The young hawks fledge at about 50- 60 days. Both the incubation and fledging periods are longer than other Buteo species. Juveniles will not enter territorial breeding areas until sexual maturity is reached at the age of three (Thornton 1971, del Hoyo, J., et al. 1994).

Behavior

Galapagos Hawks show little fear of man, probably due to the fact that they have no natural predators on the islands. There have been documented incidents of field researchers being allowed to pet the wild hawks in their natural habitat. However, when young are present, adults demonstrate a strong territorial defense attempting to drive of percieved threats to their young.

The hawks live, roost and hunt in family groups of two or three. When hunting, the groups keep in sight of each other while soaring at a height of 50-200 meters (150- 650 ft). The members of the group will signal to one another when a carcass or prey has been found. During feeding, one hawk will dominate the food source and prevent the other family members from eating the carcass until satisfied. Apparently, the submissive hawks never challenge for dominance, preferring to wait until the dominant hawk is finished eating.

Mating begins in flight where the males make mock attacks on the female from above and slightly behind. Males follow the female as she descends to the trees below, where copulation occurs. Peculiar clucking noises are often heard during copulation. After copulation the males' flight patterns are slow and low to the ground.

The male hawks tend to be monogamous, while the females will mate with up to seven different males in a breeding season. Throughout the nesting period, the female and her males take turns incubating the eggs, feeding the young and defending the nest, while the others are away (Thornton 1971, del Hoyo, J., et al. 1994).

Communication and Perception

Food Habits

Galapagos Hawks are carnivorous and are skilled hunters. Their diet consists of lizards, rats, doves, centipedes, Audubon's Shearwaters Puffinus iherminieri iherminieri, both land and marine iguanas, small goats, boobies, and grasshoppers. They will also scavenge on almost any form of carrion with the exception of marine iguanas, seals and sea lions, the latter maybe due to the hide on the seals and sea lions being too thick to rip open. Galapagos Hawks will occasionally obtain a free meal by following fishing boats and goat hunters who toss out scraps (De Vries, in litt., Thornton 1971, del Hoyo. J., et al.1994, Howard, et al. 1994).

Economic Importance for Humans: Positive

Settlers introduced rats to the Galapagos Islands. Galapagos Hawks now include the rats in their diet, which helps control the rat population. (Thornton 1971).

Economic Importance for Humans: Negative

Galapagos Hawks have posed a problem for the settlers of the islands by preying upon their poultry and livestock (Thornton 1971).

Conservation Status

Status: Rare (del Hoyo, J., et al. 1994)

Other Comments

Humans have hunted the Galapagos Hawk almost to extinction for destroying their poultry and other small livestock. As of 1971, reportedly there were only 200 pairs of the Galapagos Hawks remaining in the islands. If lower levels are reached, the IUCN may need to intervene to prevent extinction (Thornton 1971, del Hoyo, J., et al. 1994).

Contributors

Daniel Licon (author), Fresno City College, Carl Johansson (editor), Fresno City College.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scrub forest

scrub forests develop in areas that experience dry seasons.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

References

1996. "Terra Quest" (On-line). Accessed July 06, 2000 at http://www.terraquest.com/galapagos/wildlife/island/hawk.html.

Arnold, D. 1997. "Red-Tailed Hawk" (On-line). Accessed July 06, 2000 at http://www.animaldiversity.ummz.umich.edu/accounts/buteo/b._jamaicensis$narrative.html.

Howard, R., A. Moore. 1994. A Complete Checklist of Birds of the World. New York: Academic Press.

Thornton, I. 1971. Darwin's Islands: A Natural History of the Galapagos. New York: The Natural History Press.

Wheeler, B., W. Clark. 1995. A Photographic Guide to North American Raptors. New York: Academic Press.

del Hoyo, J., A. Elliot, J. Sargatal eds.. 1994. Handbook of the Birds of the world Vol. 2 New World Vultures. Guineafowl.. Barcelona: Lynx Edicions.