MORPHOLOGICAL VARIABILITY OFCICONIA BOYCIANA(AVES: CICONIIDAE) TRACKS IN HOMOGENEOUS SEDIMENT

Abstract

ABSTRACTThe morphological variability of Ciconia boyciana (oriental white stork) tracks is documented in an actualistic ichnological experiment using wet potter's clay. Measurements were obtained from 54 tracks left by two individuals comprising area, length, width, depth, volume, and rotation for each track. The trackmakers were also filmed while walking. An anatomical feature unique to C. boyciana is that, unlike other wading birds, it does not leave metatarsophalangeal pad impressions. This feature can be used to distinguish C. boyciana tracks from those left by other birds of similar body weight and habitat. Track width varied by up to 30%, with wider tracks showing more splayed digits occurring in trackways with shorter stride length and larger trackway width. Conversely, narrow trackways with a large stride length were composed of tracks with a smaller digit divarication. Coefficient analysis of track geometry revealed that the widths and depths of tracks vary inversely to maintain a consistent volume. Sorting the C. boyciana tracks into morphological types (14 types for avians with four digits) demonstrates the result that most tracks are deeper between digits III and IV than between digits II and III. Combining track data with video footage shows that C. boyciana moves its hips from side to side while walking. Noting that the tracks within any given trackway are outwardly rotated, we interpret this track morphology as resulting from laterally directed pressure exerted primarily through digit IV.