mise à jour du
13 janvier 2008
J Field Ornithol
Head scratching and yawning in Black Skimmers
Robinson SR

Dep zoology. University Wisconsin.USA


black skimmers
Several hypothese have been advanced concerning the functions of avian head-scratching including preening of the head plumages, preading of uropygial oil on head feathers and relief of local irritations on the head (Burt & Hailman, Ibis 120:153-170, 1978).
A fourth hypothesis holds that head-scratching may help to alleviate pressure differences in the middle ear or eustachian tubes. This idea derives from Andrew's (Br. J. Anim. Behav. 4:85-91, 1956) observation that head-scratching often is directed at the external opening of the ear, and that it sometime is associated with yawning. However, since Andrew's study I have found no published data that confirm this relationship between head-scratching and yawning.
On 20 Mar. 1978, I watched 15 to 20 Black Skimmers( Rynchops niger) head-scratching (by bringing one foot directly up to the head, under the wing) and yawning (by opening the bill for 1-2 sec) as they stood on a beach by Lake Okeechobee Florida.
If one of the functions of head-scratching is to help clear the eustachian tubes ,as y awning presumably does, then one would expect yawning to be associated only with head-scratches that contact the head near the external ear opening; scratches that contact the head in other areas, such as near the bill or on the top or back of the head, would presumably be in response to other stimuli and should not be associated with yawning.
I observed 26 different bouts of head-scratching among these Skimmers:1 0 of 15 scratches (67%) that contacted the head near the ear were followed within a few seconds by yawning,but none of 11 scratches that contacted the head elsewhere were followed by yawning.
This relationship of ear directed scratches with yawning is significant ( x2 = 11.92, df = 1, P< 0.001), and although it does not prove the internal pressure hypothesis it is consisten with the hypothesis and Andrew's original observations and suggests that hidden internal changes may affect the occurrence of head-scratching.
bac en ciseau noir
Grattages de tête et bâillements chez l'oiseau Bec en ciseau noir (Rynchops niger)
Le comportement des oiseaux de se gratter la tête avec l'aile modifie les pressions dans l'oreille moyenne, en ouvrant l'orifice externe de l'oreille. Cela est souvent associé à des bâillements, qui sont connus pour ouvrir la trompe d'Eustache.
En mars 1978, SR. Robinson observa un groupe d'une quizaine d'oiseaux (Le bec en ciseau noir) Rynchops niger au bord d'un lac de Floride. Il nota 26 fois ce comportement de frottement de la tête avec l'aile. Dans 67% des cas ce mouvement était suivi d'un bâillement. Une coincidence parait bien peu probable.