Excerpt from Bird Hazard to Aircraft

Much remains to be learned about the altitudes at which birds fly under various weather conditions at different seasons of the year. The following is a general summary of bird flight information as known at present. Although primary emphasis is given here to coastal areas and major water courses, heavy concentrations of waterfowl and other large birds also occur over a number of wildlife refuges in various parts of the United States. Persons interested in potential hazard areas in specific States should contact the Bureau of Sport Fisheries and Wildlife and State conservation departments for details relating to local bird concentration areas.

Songbirds generally fly within 5, 000 feet of the ground. At night these small birds commonly fly as widely scattered individuals rather than in dense flocks; at times, however, concentrations may build up at night over shorelines when prevailing winds have a tendency to drift the birds toward the ocean or the Great Lakes. During daylight hours some Species of song birds fly in dense flocks.

Concentrations of large-sized birds are more frequent in coastal than in inland localities. Unfortunately, many major airports have been constructed in tidal locations even on reclaimed land partially sur rounded by tidewater. This automatically creates serious and complex problems because of the variety of birds and the heavy transient populations that pass through coastal areas even when the airport itself offers no particular attraction.

From what is known of the geography of bird abundance in the United States, the Atlantic, Pacific, and gulf coasts and adjacent marshes would be potential hazard areas below 6, 000 feet, day and night, from late August through late April. The hazard would continue locally through the summer on the coasts of Maine, New Hampshire, and Massachusetts (gulls up to about 4, 000 feet); Connecticut to North Carolina (terns, chiefly below 500 feet; gulls in some areas up to 4, 000 feet); South Carolina to and including Texas (pelicans, terns, and herons, chiefly below 500 feet; gulls in some areas up to about 4, 000 feet); and on the Pacific coast and offshore islands (gulls and cormorants up to about 4, 000 feet). The majority of coastal birds are within 5 miles of shore, but tens of thousands of large, low-flying shearwaters (mostly below 500 feet) may be present, especially off the central and southern California coast, June through August.

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