A. Distribution.
1. Representatives of Falconidae, Accipitridae, and Pandionidae can be found on every continent worldwide, except Antarctica. Some species, like the osprey and peregrine falcon, are global. Others, like the Seychelles kestrel (Falco araea) of the Seychelles islands, are restricted to certain regions.
2. The secretary bird is endemic (restricted) to sub-Saharan Africa.
3. New World vultures are found in the Western Hemisphere, specifically North and South America.
4. Old World vultures are found in the Eastern Hemisphere, including Europe, Asia, and Africa.
B. Habitat.
1. A diurnal bird of prey species can be found in almost every type of habitat, from the Arctic tundra to the desert.
a. Populations of peregrine falcons and gyrfalcons (Falco rusticolus) breed in the Arctic. Peregrines prefer tundra, while gyrfalcons prefer the northern edges of boreal forests.
b. Species found in desert habitats include prairie falcons (Falco mexicanus) in the U.S. and Mexico, and lappetfaced vultures (Torgos tracheliotus) in Africa.
c. Ospreys and bald eagles occupy areas near lakes, rivers, and coasts.
d. Many species prefer forest habitats.
(1) Sharp-shinned hawks (Accipiter striatus) and northern goshawks (Accipiter gentilis) are generally found in or around coniferous forests.
(2) Cooper's hawks and red-shouldered hawks (Buteo lineatus) prefer deciduous forests.
(3) Harpy eagles (Harpia harpyia) live in South American rain forests.
e. A number of species can be found in grassland habitats, including the Swainson's hawk (Buteo swainsoni). Savannas, which are tropical and subtropical grasslands with scattered trees, support a variety of species including whiteheaded vultures (Trigonoceps occipitalis) and bateleur eagles (Terathopius ecaudatus).
2. Some species can exploit a variety of habitats while others are restricted to one type of habitat.
a. American kestrels (Falco sparverius) are widely distributed and ecologically versatile. They can be found in alpine areas down to deserts, grasslands, forests, and human suburbs.
b. Habitat specialists include the snail kite (Rostrhamus sociabilis), which is restricted to freshwater marshes by its diet of apple snails.
3. Migratory species occupy both breeding and nonbreeding habitats.
C. Migration.
1. True migration in birds involves a seasonal movement (usually fall and spring) between a breeding region and a nonbreeding or "wintering" region.
a. Migration enhances survival for birds whose breeding grounds have harsh winters.
b. Conversely, migration allows birds to return to breeding areas that have abundant food supplies for raising young.
c. The majority of migration routes have a north and south direction. About 95% of all land birds breeding between 40o and 50o North latitude fly south for the winter (Welty, 1982).
d. Migrating birds are thought to have an "internal calendar" which determines the correct time to start migration. The internal calendar is fine-tuned by prevailing environmental factors, such as photoperiod (day length).
e. Birds are believed to navigate by using an inherited internal map as well as the position of the moon, stars, and sun; the earth's magnetism; landscape features; and/or past experience.
f. To supply the considerable energy needed for migration, birds accumulate extra body fat two to three weeks before departure.
2. Patterns and distances of migrations vary between species.
a. Long-distance migrants include the Swainson's hawk and the tundra-breeding peregrine falcon (Falco p. tundrius). A banded Swainson's hawk traveled 11,500 km (7,146 mi.) from Saskatchewan to Argentina in 126 days. A peregrine falcon flew from Canada's Northwest Territories to Argentina in 174 days, covering 15,000 km (9,321 mi.) (Johnsgard, 1990). Eastern red-footed falcons (Falco amurensis) migrate between eastern Siberia and southern Africa (Pickford and Tarboton, 1989).
b. A relatively short-distance migrator is the resident black kite (Milvus migrans) of Africa, which migrates from the southern Sahara Desert to the Cape of Africa (Pickford and Tarboton, 1989).
3. Some diurnal birds of prey migrate singly while others migrate in flocks.
a. The rough legged hawk (Buteo lagopus) usually migrates singly or in pairs.
b. Honey buzzards (Pernis apivorus) have been sighted migrating in flocks of over 200,000 individuals (Pickford and Tarboton, 1989).
4. The majority of diurnal bird of prey species are not true migrators.
a. Some species, such as the snail kite of Florida, are residents of an area year-round.
b. Other species are partial migrants.
(1) In partial migrant species, some individuals of a population are residents year-round, while others are migratory. Bald eagles are considered to be partial migrants (Kerlinger, 1989).
(2) In many partial migrant populations, one sex is more likely to reside in the breeding region all year, while the other migrates.
(a) In North American peregrine falcons and gyrfalcons, the males remain in the breeding region more often than the females (Johnsgard, 1990).
(b) The opposite is true for male and female goshawks and common buzzards (Buteo buteo) in Sweden (Kjellen, 1994).
c. A few species are nomadic. Brown snake eagles (Circaetus cinereus) move about the African savanna stopping where food is plentiful and moving on when conditions decline.
D. Home range.
1. Home range size during the breeding season depends largely on food availability. In general, if prey is abundant near the nest, home range size is small. If prey is scarce or far away, home range size is large. Differences in home range size not only exist between species, but within the same species.
a. In some regions of Africa where prey is abundant, black eagles (Aquila verreauxii) have an average home range size of 10.5 square km (4 square mi.) (Newton, 1979).
b. In other areas where prey is harder to come by, black eagle home ranges can be as large as 260 square km (100 square mi.) (Newton, 1979).
2. Generally, the larger the species the larger the home range. Golden eagles (Aquila chrysaetos) in Wyoming have breeding home range sizes as large as 251 square km (97 square mi.). In comparison, American kestrels in Utah have breeding home ranges as small as 0.7 square km (0.3 square mi.) (Johnsgard, 1990).
3. Birds will defend all or part of the breeding home range if food and nest sites are scarce, and defense from intruders is physically possible. The area actively defended is a bird's territory.
a. Some species, like the red-tailed hawk, defend their entire home range, which varies from 1.3 to 24.9 square km (0.5-9.6 square mi.) per breeding pair (Johnsgard, 1990).
b. Other species defend just the nest site, or a limited area around the nest site, and have overlapping home ranges. Prairie falcons (Falco mexicanus), which have been recorded with breeding home ranges of about 26 square km (10 square mi.), fall in this category (Johnsgard, 1990).
c. European kestrels (Falco tinnunculus) defend their entire home range of about 3 square km (1 square mi.) at the start of the breeding season, but have overlapping home ranges by the end of the season (Newton, 1979).
d. In nonmigratory species, breeding territories may be defended all year. In migratory species, breeding territories are reestablished each year.
4. Migratory species may also establish winter home ranges. Some species, like American kestrels, even hold winter territories if food availability is low.
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