IdentificationPeregrine falcons, like all falcon species, are designed for speed. With long, pointed wings, a long, tapered tail and flat head, peregrines can attain rapid speeds in powered flight or stoops. Attaining dive speeds of up to 200 M.P.H., the peregrine falcon is the planet's fastest bird. Its wing beats are stiffer and deeper than those of other falcon species. In a soar, they exhibit a soft-angled silhouette resembling that of a cocked bow and arrow. Significant sexual size dimorphism is displayed by peregrine falcons, the females of which can be as much as one-third larger than males. In addition, the crow-sized males are considerably slighter and narrower winged than females. The peregrine falcon's call is a series of quick, loud, kee notes.Adult peregrines are blue-gray above with a dark head and flight feathers and a paler rump. From below, adults are whitish with dark barring on the chest and underwing. Like most falcon species, peregrines show a distinct sideburn or "moustache" mark each side of the face. The cere--the fleshy area behind the base of the bill that contains the nostrils--and legs are yellow, the bill is black, and the eyes are dark brown.Juvenile peregrine falcons are dark slate-brown on the upperside and often show a contrasting blonde crown. The underside is buff colored with dark brown checker-marked underwings and vertical streaks on the chest. The cere and legs are pale blue and the bill is black. Adult plumage is acquired the summer after fledging.

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Eggshell thickness after exposure to DDT was reduced by 21.7 percent in Alaskan tundra peregrines, by 16.8 percent in taiga peregrines, by 7.5 percent in Aleutian peregrines, by 3.3 percent in rough-legged hawks, and not at all in gyrfalcons. Tundra peregrine eggs contain an average of 889 parts of DDE per million (lipid basis); taiga peregrine eggs contain 673 parts per million; Aleutian peregrine eggs contain 167 parts per million; rough-legged hawk eggs contain 22.5 parts per million; and gyrfalcon eggs contain 3.88 parts per million. These changes in eggshell thickness and the pesticide residues reflect different degrees of exposure to contamination. There is a highly significant negative correlation between shell thickness and DDE content in peregrine eggs. Tundra and taiga peregrines have fledged progressively fewer young each year since 1966.

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