Christmas Bird Count

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American Kestrel © Marty DeAngelo

The decade-interval map illustrates low numbers of American Kestrels on CBC's in 1958, with a steady increase in numbers found per party-hour until 1988, then a notable drop to 1997. The low numbers in the '50's, increasing until the '90's, may well represent a comeback in numbers of kestrels following the banning of the use of the pesticide DDT in the 1960's. To view larger version of animated map, click on map image.

The fluctuation in numbers of kestrels on Christmas Bird Counts in the 1990's, detailed in the second map, perhaps shows how this small falcon fares after harsh winters, or at least how far the migratory birds have moved by early winter. In addition, the conversion of much agricultural land to urban areas could adversely affect American Kestrels; nesting cavities, fields and thickets, and the American Kestrel's prey base itself may be in decline over many areas of North America. To view larger version of animated map, click on map image.

This species' Breeding Bird Survey trend map available at the Patuxent Wildlife Research Center's website documents a patchwork quilt across North America, with nesting kestrels increasing some regions and decreasing in others.

Formerly called "Sparrow-hawk," the American Kestrel (Falco sparverius) is a lovely, small, widespread falcon of the Western Hemisphere. Possessing an amazing breadth of both latitudinal range (from the edge of the Arctic tundra to Tierra del Fuego) and selected habitat (found in virtually all terrestrial habitats except dense forest), kestrels are familiar to city dwellers and field birders alike. Extreme northern and southern populations are migratory, with some birds heading to warmer climes in their respective winters. Kestrels are sexually dimorphic; females are larger with rusty wings, while males are smaller with bluish-gray wings. They feed primarily on small mammals and insects, but will take other food items including small birds.

Though remaining fairly common, as illustrated by the Christmas Bird Count-based species abundance maps below American Kestrels have gone through several population cycles in the past decades. This is not surprising for several reasons. Kestrels wintering in North America are at one extreme of their geographic range, and they are probably more susceptible to hardships of winter weather. Also, they are primarily carnivorous, and much of their diet consists of what humans consider as pests—insects and mice. Therefore, American Kestrels could well suffer directly from pesticide applications used to control their prey items. In addition, North American populations of the American Kestrel move considerable distances in the winter, and face more potential survival threats over a greater geographic area than resident or short-distant migrant species.

The maps below show several cycles of ebb and flow of American Kestrel numbers on Christmas Bird Counts over the past half century. The most recent years show a decline in numbers, as has been often reported in the Regional Editors’ comments in the printed Christmas Bird Count results. It is important to note that the abundance maps displayed below are generated based upon birds reported per party-hour on Counts, and not raw numbers of kestrels reported. Since kestrels are common and conspicuous birds, more observers in the field for more time on any given count will sight more birds. When data are presented based on birds per party-hour, changes in numbers of birds can be seen, not confused by variance in observer effort.