Peregrine Falcon Habitat Model
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Draft Date:
May 2001

Species:
Peregrine Falcon, Falco peregrinus

Use of Study Area Resources:
Reproduction, rarely winters as far north as eastern Massachusetts. Peregrine falcons were once widely distributed, but have been largely extirpated. Western populations breed in Alaska and Canada, southwards to Mexico on the Pacific coast. They have been reintroduced in the Northeast from captive bred birds.  Peregrine falcons now nest within the study area in Massachusetts, New Hampshire and Maine on cliff habitats and some high-rise urban structures that functionally mimic cliffs (Corser et al. 1999). Winter habitats consist of coastal regions from the mid-Atlantic through Central and South America (National Geographic Society 1987).

Habitat Requirements:
Nesting. Optimal nesting habitat consists of a cliff face over 200 ft (61m) high, and 500 ft (150m) or more in length, with more than one good nesting ledge, a wooded slope or open land below, and isolated from roads or other human disturbance (Hagar 1969). Nesting cliffs often have a southern exposure (Stokes and Stokes 1989). Characteristics of a good nesting ledge include substrate into which an indentation can be scratched to contain eggs, with a rocky overhang to protect eggs and young from direct sun or rain (Rice 1969). Preferred nest sites are typically midway up or down the cliff face, and offer multiple ledges for nesting, roosting, and feeding (Stokes 1989). In rare cases when other sites are unavailable, peregrines have been documented nesting in trees, using old eagle or hawk nests, or on broken snags, but they are not nest builders (Hickey 1969; Terres 1995). During the breeding season, male and female peregrines roost in separate spots along the nesting cliff (Stokes 1989), or structure (Cade and Bird 1990). Use of man-made structures for nesting is well documented on urban roof-tops, bridges (Cade and Bird 1990), smokestacks (Cade et al. 1994), and power generation stations (Septon 1994).

Foraging. Peregrines hunt on the wing and are well known for taking pigeons, as well as a variety of shorebirds, seabirds, ducks, and other small to medium sized birds that include kestrels, kingbirds, flickers, jays, crows and blackbirds. They also occasionally take insects, small mammals (especially bats) and fish (Cade and Bird 1990, Terres 1995, Amies 1997). Peregrines may travel up to 28 km to favorite foraging areas (FWIE/ESIS).

Sensitivity to Disturbance. Peregrine falcons are among the most strident of nest defenders. Tolerance of disturbance varies among individuals, and with seasonality and timing of the breeding cycle, but peregrines will actively defend an area around the nest and that ranges outward from 300 m to as much as 1.6 km (FWIE/ESIS). Historic causes of mortality and extirpation have included pesticide contamination (Peakall 1976, Peakall et al. 1990), disturbance by road construction, blasting, recreational activities too close to nest sites, removal of young from nests for falconry, and removal of eggs from nests by collectors (Herbert and Herbert 1969).

Habitat Mapping:
Habitats were mapped using a model and available occurrence information.  Peregrine nest site locations were obtained from the New Hampshire and Maine Natural Heritage Programs, and from Brad Blodgett, Massachusetts Division of Fisheries and Wildlife. Of the 75 locations, 5 were in artificial habitats (bridges, buildings).  The balance were used to examine associations with available environmental data layers which might be used to model nesting locations.  

In order to see whether nesting cliffs could be identified, we overlaid occurrence data on a map of slopes.  Taking into account the relative abundance of each class of slope (e.g., 0 to10 degrees, 11 to 20 degrees, etc.) throughout the study area, we found the occurrences were strongly associated with the steepest slopes.  We scored slopes of 11 to 30 degrees as suitable (0.5) and slopes > 30  degrees as preferred (0.7 - reserving a score of 1.0 for known nest sites).

We similarly examined the association of occurrences with aspect and found that more than would be expected faced east, through southeast, south, southwest, and west.  These directions were scored 1.0. 

Modeled nest habitat was the product of slope and aspect suitabilities.  We retained habitat patches 2 acres or larger.  This corresponded with 53 of the 58 natural occurrences, and 1 artificial (high bridge) site. The 5 natural sites missed were on the coast of Maine; resolution of our elevation data may not have been adequate to distinguish aspect and slope of coastal bluffs.  These coastal, and all other sites, were mapped by buffering them at a 0.25 mi radius, and scoring these areas 1.0.

Sources:
Amies, P. 1997. Peregrine falcon apparently catching and eating insects in flight. British Birds 90(9):358-359.

Cade, T.J. and D.M. Bird. 1990. Peregrine Falcons, Falco peregrinus, nesting in an urban environment: a review. Can. Field-Nat. 104(2):209-218.

Cade, T., M. Martell, P. Redig and H. Tordoff 1994. Peregrine falcons in urban North America. J. Raptor Res. 28(1):44-45 (abstract only).

Corser, J.D., M. Amaral, C.J. Martin and C.C. Rimmer. 1999. Recovery of a cliff-nesting peregrine falcon, Falco peregrinus, population in northern New York and New England, 1984-1996. Can. Field-Nat. 113(3):472-480.

FWIE/ESIS webpage: http://fwie.fw.vt.edu/WWW/esis/lists/e109002.htm downloaded 9/21/99. Fish & Wildlife Information Exchange, Virginia Polytechnic Institute & State University.

Hagar, J.A. 1969. History of the Massachusetts Peregrine Falcon Population 1935-1957. Pp. 123-132 in J.J Hickey (ed.) Peregrine Falcon Populations: their biology and decline. University of Wisconsin Press, Madison, WI. 596 p.

Herbert, R.A. and K.G.S. Herbert. 1969. The extirpation of the Hudson River peregrine falcon population. Pp 133-154 in J. J. Hickey (ed.) Peregrine Falcon Populations: Their Biology and Decline. University of Wisconsin Press, Madison, WI. 596 p.

Hickey, J.J. 1969. Peregrine Falcon Populations: Their Biology and Decline. University of Wisconsin Press, Madison, WI. 596 p.

National Geographic Society. 1987. Field Guide to Birds of North America, 2nd edition. National Geographic Society, Washington, DC, p 204.

Peakall, D.B. 1976. The peregrine falcon and pesticides. Can.Field-Nat. 90:301-307.

Peakall, D.B., D. Noble, J.E. Elliott, J.D. Somers and G. Erickson. 1990. Environmental contaminants in Canadian peregrine falcons, Falco peregrinus: a toxicological assessment. Can. Field-Nat. 104(2):244-254.

Rice, J.N. 1969. The decline of the peregrine falcon population in Pennsylvania. Pp. 155-164 in J.J. Hickey (ed.) Peregrine Falcon Populations: Their Biology and Decline. University of Wisconsin Press, Madison, WI. 596 p.

Septon, G. 1994. Peregrines, power plants and migration routes. J. Raptor Res. 28(1):50.

Stokes, D. and L. Stokes. 1989. A Guide to Bird Behavior. Little, Brown and Co. Pages 173-189.

Terres, J.K. 1995. The Audubon Society Encyclopedia of North American Birds. Wings Books, Avenel, NJ.