Drinking of the Pigeon (Columba Livia L.)

TLDR: The application of a comparator model for the description of the stereotypy of the pecking behaviour for the drinking behaviour showed that the drinking swallowing cycle and the three types of eating swallowing cycles were basically similar and a possible evolutionary scenario for the double-suction mechanism was discussed.

Abstract: 1. The consummatory part of the drinking behaviour of pigeons is studied by a frame-by-frame analysis of high-speed films and X-ray motion pictures. 2. A double-suction or vacuum-pump model is formulated for the mechanics of drinking. Consummatory drinking is a series of similar movement cycles, each transporting one dose of water into the oesophagus. The swallowing movement cycle shows five phases: 1, capillary action of the beak tips; 2, lingual suction; 3, pharyngeal preparation; 4, pharyngeal suction; and 5, oesophageal collection. A double build up of an area of low air pressure occurs. As a result of the retraction of the tongue in the mouth (acting as a piston in a cylinder) low air pressure develops in the buccal cavity and water is sucked into the mouth. Secondly, a lower air pressure area develops in the pharynx as a result of a depression of its floor, so that the water in the mouth is given a momentum caudad, by which it is forced over the larynx into the oesophagus. Neither peristaltic action, nor an alternative lower air pressure area is recorded in the oesophagus. The collection of the swallowed water at the lowest place occurs by gravity. 3. Using the mechanical requirements of the double-suction model the presence and distribution of glands was predicted. As predicted the following glands were found: the gl. lingualis superior et inferior, the gl. mandibularis anterior et posterior, the gl. palatina posterior externa, the gl. cricoarytenoidea and the gl. sphenopterygoidea. 4. The application of a comparator model for the description of the stereotypy of the pecking behaviour for the drinking behaviour showed that the drinking swallowing cycle and the three types of eating swallowing cycles were basically similar. The difference, apart from those of amplitude, was the coupling of the erection of the ventral pharyngeal valves to the pro- and retraction of the linguolaryngeal apparatus. The erection occurs during drinking at the very start of the protraction, but during pecking at the start of the retraction. Further, the consummatory act of drinking is composed of some smaller fixed elementary movement units. These units are fixed for mechanocybernetical reasons. The decision points between these units though masked under normal conditions, were found at the start of the capillary phase and during the preparatory phase by experimental manipulation. 5. A possible evolutionary scenario for the double-suction mechanism is discussed. It is suggested that: 1, the feeding system is maximized for food transport by using the slide-and-glue mechanism rather than using the ancestral catch-and-throw mechanism; that 2, the feeding system was maximized for water transport by using the double-suction mechanism rather than the ancestral tipping-up mechanism; that 3, high selection pressure on fast transport of seeds has occurred and that lack of selection pressure on fast drinking was probable. From this may be concluded that the slide-and-glue mechanism is the primar mechanism and the double-suction secondar. This secondary development is in itself a simple change of coupling of one of the subunits already developed as a pecking submechanism, the erection of the ventral pharyngeal valves. Although this recoupling falls completely within the mechanical boundary conditions of the slide-and-glue mechanism so that no reconstruction of the mechanical part of the system is required, nevertheless some strong selection pressure might be necessary for the evolution of a double-suction mechanism since valve erection was found to be part of different centrally coordinated fixed elementary units in swallowing both during eating and drinking. Such an external selection pressure could not be found. Finally, it was shown that for the explanation of the evolutionary scenario of suction drinking the "monistic adaptationist programme" was not sufficient, and a dualistic neodarwinian approach and a multifactor analysis were advocated.