Spatial Disorientation in Birds

T HE aircraft was on final approach through the rain and fog. At approximately 500 feet it went into a spiral dive to starboard, striking the right wing against the approach lights. The aircraft was destroyed. Blackburnian Warblers were migrating on a night of a low ceiling and the visibility restricted in moderate rain. On reaching a floodlighted area, some fifty birds crashed into a hangar and were killed. Initially there does not seem to be much in common, except the weather, in these two unfortunate occurrences. Yet, under analysis, there may be a great deal of similarity. In both cases the fliers were attempting to fly through deteriorating weather conditions, pickin g their way through a maze of light and shadow, of reflected and refracted light shining through rain, an opaque obstructing medium. It is suggested that the cause of both the crashes was exactly the same. The fliers became confused by the abruptness of intense lighting, and, using the primary sense of orientation (sight) in conjunction with erroneous sensory stimuli, suffered a complete loss of spatial orientation. Birds, particularly the nocturnal migrants when flying at low level are susceptible to, and suffer from vertigo and spatial disorientation the same as man. For the purpose of this discourse it is assumed that: (a) the aerodynamic forces acting on the wings of a bird are the same as those acting on the wings of an aircraft; (b) only nocturnal migrants are under consideration; (c) the sense organs are used for the same basic purposes in both birds and man; and (d) while the senses of the bird may be more acute, the psychophysiological reactions to the stimuli are similar in birds and man. Although the aerial environment is applicable to both birds and man, each has its own peculiar environment in which it flies and this is not readily examinable by direct observation. This environment is made up of stimuli appreciated by sensory organs and perceived by the brain. The reactions to the stimuli are based upon knowledge, and each reaction must be correct in the proper place at the proper time. Because the human pilot is sensitive to similar stimuli, man can visualize the aerial world of other fliers. It is only through a comparison of the bird with man’ s knowledge of flying that we can deduce how a bird flies. As spatial disorientation is extremely common (90 per cent incidence) amongst all-weather pilots, the most expedient way of determining the happenings and causes of spatial disorientation in birds is to consider first the human pilot.