Height Distribution of Birds Recorded by Collisions with Civil Aircraft

The National Wildlife Strike Database for Civil Aviation in the United States contained 38,961 reports of aircraft collisions with birds (bird strikes) from 1990––2004 in which the report indicated the height above ground level (AGL). I analyzed these strike reports to determine the distribution of all strikes and those strikes causing substantial damage to aircraft by height. For the 26%% of strikes above 500 feet (152 m) AGL (n == 10,143), a simple negative exponential model, with height as the independent variable, explained 99%% of the variation in number of bird strikes per 1,000-foot (305-m) interval. Strikes declined consistently by 32%% every 1,000 feet from 501––20,500 feet (153––6,248 m). For strikes at ≤≤500 feet, passerines, gulls and terns, pigeons and doves, and raptors were the identified species groups most frequently struck. For strikes at >500 feet, waterfowl, gulls and terns, passerines, and vultures were the species groups most frequently struck. For strikes that resulted in substantial damage to the aircraft, 66%% occurred at ≤≤500 feet, 29%% between 501––3,500 feet (153––1,067 m), and 5%% above 3,500 feet. A higher (P < 0.001) proportion of strikes between 501––3,500 feet caused substantial damage to the aircraft (6.0%%) than did strikes at ≤≤500 feet (3.6%%) or at >3,500 feet (3.2%%). For strikes at ≤≤500 feet, July––October were the months with the greatest proportion of strikes relative to aircraft movements. For strikes at >500 feet, September––November and April––May had more strikes than expected. About 61%% of the reported strikes above 500 feet occurred at night, compared to only 18%% of civil aircraft movements. Thus, about 7 times more strikes occurred per aircraft movement at night compared to day above 500 feet. This analysis confirmed that management programs to reduce strikes should focus on the airport environment because 74%% of all strikes and 66%% of strikes causing substantial damage occur at ≤≤500 feet. To minimize significant strike events occurring outside the airport (>500 feet), efforts to predict or monitor bird movements using bird avoidance models and bird-detecting radar need to focus on heights between 500 and 3,500 feet AGL, with special emphasis on night movements of birds during April––May and September––November.