Birds and Aircraft on Midway Islands, 1959-63 Investigations

Abstract

At Midway Naval Station, 1.100 miles west-northwest of Honolulu, military aircraft collide with flying albatrosses at the rate of about 300 to 400 per year. One aircraft out of every five that hits an albatross on takeoff either aborts (stops before it is airborne), or dumps fuel and returns for appraisal of damage. About 70,000 pairs of Laysan albatrosses and 7,000 pairs of blackfooted albatrosses nest at Midway in any given year. The population is declining. Two-thirds or more of the birds of breeding age nest each year. The minimum breeding age recorded is 5 years (each species), but many individuals do not nest until at least 7 years of age. Young birds begin to return to Midway at 3 years of age and are found more frequently as breeding age approaches. They come ashore more frequently in March and April (the high bird strike months) than in midwinter. Even in midwinter the number of 'walkers' (birds not on nests) may comprise more than 40 percent of the albatrosses present on Sand Island, Midway. Maximum longevity of the Laysan albatross is believed to exceed 40 years; 6 out of 99 birds banded as breeding adults (7+ years old) were still alive 24 years after banding. Control methods tested experimentally include disturbance, gunfire, other sounds, radar beams, smoke, odors, destruction of nests, eggs, chicks, and adults, moving of birds, eggs, and chicks, erection of obstacles to flight, and habitat management. Habitat management (leveling and hardsurfacing of shoulders of runways) has been the most effective. Albatrosses were counted over the runways at 10 locations in 1957, 1958, and 1960 to determine the effects of wind direction, wind speed, and topography on the numbers of flying birds. Birds were most concentrated in areas where rising air currents were created as winds blew against dunes or tall trees. Soaring and strike rate both increased with greater wind speeds. There was a highly significant correlation between strike frequency and wind direction. Soaring and strike rate were greatest over runway 6-24 when winds were from a northerly quadrant, and greatest over runway 15-33 when winds were east to southeast. Counts (nearly 7,000 observations) before and after the leveling of dunes along part of the south side of the principal runway, 6-24, showed a 61 percent decrease in soaring over the principal runway as compared with a 4 percent increase over runway 15-33 where no major habitat management had been done. Studies of population dynamics of Laysan and black-footed albatrosses in 4 study plots (totaling 14 1/2 acres) are yielding information on nesting density, changes in nesting population from year to year, frequency of nesting of individual birds, closeness of return, reproductive success, rate of nest loss, age at which young birds begin nesting, age composition of the population, and life expectancy of adults. Recommendations are made for reducing the bird hazard and for protecting birds that are not involved in the hazard.