Ardea
Official journal of the Netherlands Ornithologists' Union

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van Rhijn J.G. (1977) Processes in feathers caused by bathing in water. ARDEA 65 (3-4): 126-147
This paper describes how bathing may influence the water content and the quality of a bird's plumage in particular of some Anatidae and the Herring Gull. The water absorption by a feather depends on the intensity of the water contact (Fig. 1 A), the movement of the feather in the water (Fig. 1 B), and the duration of the water contact (Fig. 1 C). It is accelerated by high temperatures of the water (Fig. 1 D) and by a low surface tension of the water (Fig. 1 E and Table 1). Preenoil seemed to playa minor role in the protection against water absorption (Table I). Only the feathers from the ventral side and from the surroundings of the oil gland absorbed slightly more water after removal of oil. Water absorption seems to be a function of the size of the feather's surface (Table 1). Drying of a feather is strongly accelerated by shaking movements (Fig. 1 F). Apart from the direct removal of water, shaking may playa role in the dispersion of tiny water droplets over the feather, resulting in an acceleration of the evaporation of water (Fig. 2). Water absorption of a feather is higher after wetting with an interruption of a few minutes, than after the same amount of wetting without interruption (Fig. 3). This phenomenon is probably due to the fact that the water slowly penetrates into the feather as long as some water adheres to the feather's surface. Wetting results in a decrease of the stiffness of the shaft of a feather (Fig. 4). This decrease is probably a function of the amount of water penetrated into the feather. Feathers become pervious to water if they are wet on both sides. Shapes of wet feathers can be changed by means of pressure (Fig. 5). The original shape can be restored by wetting. It is likely that wetting results in a partial removal of dirt. At the end of this paper I have drawn some connections between the results on simulated bathing, and on data of real bathing of a Herring Gull. Firstly, some comments have been made to explain the large water absorption by the experimental feathers. Secondly, the effects and the patterning (Table 2 and Fig. 6) of the separate bathing movements have been discussed. The most common wetting movement (head-dipping) causes a rather poor wetting 'of the outer plumage. The movement 'wing-flapping' is probably not primarily serving the wetting of the plumage. It is mostly followed by 'wing-beating' (Fig. 7), a drying movement. 'Wing-flapping' may playa role in the removal of dirt from the wings. The movement 'plunging' causes an intensive wetting of the plumage. It is not clearly associated with drying movements.' Bill movements during bathing play a minor role in the wetting of the plumage. 'Head-scratching' may indirectly (via head-dipping) cause an intensive wetting of the head. 'Rubbing' may be performed in order to carry water from the head towards other parts of the plumage. The bathing methods of the Herring Gull seem to be rather well comparable with those of other water birds. A comparison has been made with the bathing of land birds.


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