The American Kestrel (Falco sparverius ) is the smallest, most colorful,
and common of the falcons that occur regularly in the Kittatinny-Shawangunk
raptor corridor. They are open-field-oriented falcons that typically are found
in agricultural and other old fields. The number of American Kestrel nest
territories sometimes can be high, and close to one another, as studies
demonstrated in the late 1950s and early 1960s on Charlex Farm in Albany
Township, Berks County, Pa. (see map). Natural tree cavities, old woodpecker
holes, openings in buildings, and nest boxes provide sites in which are
deposited 4 or 5 white to pinkish-white eggs covered with brownish blotches or
spots. Incubation ranges from 28 to 35 days, often 31 days. Approximately 78
percent of the eggs hatch, and cleaning nest boxes does not influence egg
hatchability rate.
In the raptor corridor, American Kestrels feed on small mammals such as
Microtus voles, Meadow Jumping Mice, and Short-tailed Shrews. Eastern
Meadowlarks, Common Grackles, Brown-headed Cowbirds, Cardinals, and Grasshopper
Sparrows also are eaten, as are grasshoppers, Periodical Cicadas (when these
insects are present), dragonflies, and beetles.
Utility poles and wires on high hills are important perches allowing
migrating kestrels to hunt, feed, and rest. When poles and wires are removed,
fewer falcons use the hilltops.
During autumn, migrating American Kestrels at Bake Oven Knob, Pa.
exhibit 10- to 12-year population cycles (see graph) which might be linked with
Microtus cycles.
Effective conservation programs for American Kestrels are relatively easy to
develop because these falcons readily accept nest boxes as nest sites if the
boxes are placed at suitable locations. That is why the Wildlife
Information Center,
and various other wildlife conservation organizations and private individuals
are placing nest boxes at selected locations along parts of the
Kittatinny-Shawangunk raptor corridor. Nest boxes can be purchased, or made by
local craftsmen from plans such as the one included in this bulletin.
Local bird watching clubs, scout troops, 4-H groups, and other interested
organizations can participate in establishing American Kestrel
nest box routes. In some cases, if human disturbance can be kept to a minimum,
kestrel nest boxes also can be placed on school grounds as part of schoolyard
wildlife refuges.
Suggested Reading
Heintzelman, Donald S.
1964 Spring and Summer Sparrow Hawk Food Habits.
Wilson Bulletin , 76: 232-330.
1966 Observations and Comments on the Aerial Capture of Prey
by the Sparrow Hawk. Linnaean News-Letter , 20
(6 & 7).
1971 Observations on the Role of Nest Box Sanitation in
Affecting Egg Hatchability of Wild Sparrow Hawks in Eastern Pennsylvania.
Raptor Research News , 5 (3): 100-103.
1975 Autumn Hawk Flights: The Migrations in Eastern North America.
Rutgers University
Press, New Brunswick, N. J.
1979 Hawks and Owls of North America.
Universe Books, New York, N. Y.
1986 The Migrations of Hawks. Indiana University Press, Bloomington, Ind.
1990 The 1957-1989 Bake Oven Knob Pa.,
Autumn Hawk Migration Field Study: A 30 Year Review and Summary. American Hawkwatcher , 17: 1-16.
1992 The Role of Perches in Limiting American Kestrel Uses of Hilltop Fields
Within the Kittatinny Raptor Migration Corridor Near Bake Oven Knob, Lehigh
County, Pa. American Hawkwatcher , 18: 2-4.
Heintzelman, Donald S. and A. C. Nagy
1968 Clutch Sizes, Hatchability Rates, and Sex Ratios of Sparrow Hawks in
Eastern Pennsylvania.Wilson Bulletin , 80: 306-311.
Nagy, Alexander C.
1962 Population Density of Sparrow Hawks in Eastern Pennsylvania.
Wilson Bulletin , 75: 93.