In order to check the validity of the “functional units” previously described from visual observations, sixteen teals were equipped with radio-tracking equipment. The movements of each bird were followed for about one month, giving rise to a total of 384 day-time and 374 night-time contacts. Eighty to 90 % of contacts demonstrate the validity of the functional unit concept : the winter quarter is divided into separate geographical sectors (the F.U.) exploited by distincts groups. Individuals of a group use the same diurnal roost, fly out at night to exploit feeding grounds which are exclusive to the group and return to the same roost the following day at dawn. Exceptional changes of roost (2 %) are accompanied by a change in feeding grounds. In addition, several new aspects of teal behaviour are described : birds are remarquably immobile during the night ; individuals transferred artificially to another roost return rapidly (0.5 to 5 days) to their original roost ; the precise position of each individual within the roost is very constant, in 84 % of cases within a radius of 500 m of the center of the roost ; each individual regularly uses the same feeding grounds (to within about 200 m) ; and finally, the position of the individual in the roost usually faces the direction of the feeding grounds. Thus the strong social organisation of teal leads to the division of the population into several groups, each one exploiting exclusively a distinct sector (the F.U.) within which new detailed patterns of spatial distribution appear. This telemetric demonstration on teal can probably be applied to those species of ducks where the same kind of social organisation and spatial distribution have already been observed, and which are probably characteristic of the majority of ducks in winter.
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Tamisier et al. (1981) studied this question.