Reports of a goshawk's top speed do not agree. One source says a goshawk chasing prey can keep flying level at up to 40 miles per hour. Another says it flies through the trees at up to 40 kilometers per hour. Neither says how the speed was measured, so the two figures do not agree. Two measured dives by a goshawk at another bird reached 23.9 and 24.2 meters per second, according to a 1987 study cited in the Birds of North America account. One wildlife education page says a goshawk may chase prey for up to 30 minutes. Still, accipiters often give up a chase after a short distance if the prey is not caught quickly.
A goshawk's wings are short and broad and not really suited for high speed, writes a Montana naturalist. The wing design and the long tail are about maneuvering through dense woods. A goshawk will fold its wings back to fly through very tight spaces between branches. Folding the wings back reduces its lift, and the bird makes up for this by fanning out its large tail. Goshawks may avoid areas of very dense forest. Young accipiters weigh less than their parents and have slightly longer flight feathers, so their wing loading is lower, which means that they fly slower and more buoyantly than adults.
A magazine column by a Montana Audubon naturalist says goshawks have more than one million light-sensing cells per square millimeter in the retina, while humans have about 200,000. An open understory helps a goshawk spot prey, and it hunts from low perches, usually under 3 feet (1 meter), in bent-over trees or saplings. It scans the lower parts of the forest, the ground and the lower canopy. Good goshawk hunting forest has space under the canopy for flight, many tree perches, and prey that can be found. Scientists learn what a goshawk eats from the pellets and prey remains found near its favorite perches.
Females are reported as weighing 860 to 1,264 grams in the Forest Service fire effects review. The Birds of North America account gives 860 to 1,364 grams, so the sources differ at the top of the range. Goshawk nesting pairs are spread thin: in the western United States there are about 3.6 to 10.7 pairs per 100 square kilometers. In the Targhee National Forest in Idaho, goshawk territory occupancy fell from 64% to 31% between 1990-1994 and 1998-2002. In the UK, goshawks were all but gone as a breeding bird by the end of the 19th century, and the breeding population has since come back. In a study, goshawks chose forest nest stands with high canopy cover, large, tall trees and an open understory.
Words to know
- retina: eye's light layer
- pellets: coughed-up leftovers
- buoyantly: lightly floating
