PERIPHERAL DEPARTMENT OF THE HEARING SYSTEM OF MARINE BIRDS (ALCIDAE). 1. MORPHOMETRIC FEATURES OF THE EXTERNAL EAR WITH AN EAR PTERYLA AND THEIR FUNCTIONAL CAPACITIES

摘要

A morphometric description and metric measurements of the external ear and the feathers of an ear pteryla are presented for three species of the family Alcidae. Their dimensions are given, together with characteristics of the angular and linear data of their mutual arrangement. A small external auditory aperture is surrounded by a narrow skin apterium. In auk birds, the auditory canal behind the ear canal widens sharply into a broad subcutaneous chamber, which cross-section exceeds 4.5-5.0 times the size of the external auditory aperture on the surface of the skin. The topographic and dimensional parameters of the canal of the external ear exclude its walls and it itself to be closed underwater by external water pressure. Ear pens form a dense wall with a low feather arch around and an air chamber above the auditory opening. The structure and arrangement of the beards on the feathers of the ear and contour feathers are such that they create a thin external water-repellent layer which does not allow the feathers to rapidly get wet and stick together. Under the arch of an ear pteryla and in the ear canal of the external ear, air is retained underwater in the form of an air plug. The air plug in the canal of the bird's outer ear can serve underwater as an air channel for transmitting sound from the aquatic environment to the eardrum and the auditory column of the middle ear. In general, the structure of the external ear with an ear pteryla in auk birds reflects the specificity of morphological adaptations to the aquatic environment.