Spatial Organization of the Epithelial Structures in the Bill Tip Organ of Waterfowl (Anseriformes, Aves)

Abstract

The spatial organization of the bill tip organ in waterfowl is studied in 327 specimens from 35 species from the Anseriform order, including geese, swans, seaducks, shelducks, dabbling, and diving ducks. Two types of tactile epithelial formations, sensillar and asensillar, are revealed on the tips of the upper and lower jaws. The number of the mandibular formations always exceeds that of the maxillary. The combinations of these indicators differ significantly among the majority of the studied species. The studied species can be divided into three types based on combinations of the number of upper and lower tactile formations according to different foraging techniques: grazing (geese, swans, sheldgeese), pursuit diving (sea ducks), and dabbling (pochards, shelducks, dabbling ducks). The formation density per square mm correlates with the asymmetry of the bill tip organ (r = 0.55; p < 0.01; n = 327). The correlation is the greatest in dabbling species. The probable function of the bill tip organ, in addition to location and analyse of food particles, lies in the fact that dabbling species can communicate with each other via motions in the course of food intake. This helps them to save time and to optimize their individual distances when feeding in darkness.