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Radar Investigations of the Bat Hazard to High Performance Aircraft at Randolph AFB, Texas

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Technical Report

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Air Force Civil Engineering Center Kirtland AFB United States

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During the months of April through October, Mexican free-tailed bats Tadarida brasiliensis mexicana are a major cause of T-38 engines failures at Randolph AFB, Texas. The airborne behavior of T.b mexicana emerging from and returning to the Bracken cave, near Randolph AFB, was observed with both search and height-finding radars. Radar echoes from dense groups of bats covered areas as large as 500 sq km and rose to altitudes of over 3,000 m. Evening bat flights appeared to have three distinct phases of development exit from the roost and ascent, transition to level flight, and dispersal. In the dispersal phase, the bats usually traveled directly toward Randolph AFB. Bat flights may be grouped into three types on the basis of their vertical distribution. One type, characterized by flight at low altitude, was usually observed on nights when T-38s were damaged. A bat avoidance program, based on real time radar observations, was initiated at Randolph AFB during the summer of 1971 and continued thru 1974. Since the start of the program, the frequency of strikes has decreased. It appears possible to predict nights when bat strikes are most likely to occur 24 hours in advance. Strobe lights were found to be an ineffective bat deterrent.

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