Ardea
Official journal of the Netherlands Ornithologists' Union

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Verheijen F.J. (1981) Bird kills at tall lighted structures in the USA in the period 1935-1973 and kills at a Dutch lighthouse in the period 1924-1928 show similar lunar periodicity. ARDEA 69 (2): 199-203
Two samples of nights on which bird kills at tall lighted obstacles were reported in the periods 1935-1973 (USA) and 1924-1928 (Netherlands) respectively, are considered as if they were circular distributions of nights in a lunar month. Both distributions prove to be non-uniform. None of the 229 reported nights falls close to the full moon. The significant mean vector of each distribution points close to the new moon. The two populations of nights from which the two samples were obtained have identical distribution functions. The obvious lunar periodicity of the kills is in accordance with the theory that an artificial light source destroys the natural angular light distribution as an orientational requirement to such a degree that birds can no longer cope with it (trapping effect as a result of photopollution). Moonlight whether or not weakened and scattered by clouds - can restore the natural spatial properties of the light field around an artificial light source to such an extent that birds can withdraw from this source. Thus it is a fallacy to argue, as is frequently done, that the moon is irrelevant to bird kills because it is invisible under the weather conditions in which most kills occur. It is concluded that reports on nocturnal bird kills at lights - objects equipped with lights include aircraft - should present relevant data about the moon.


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