The wintering ducks at the Shinobazu Pond in Ueno Park were observed from September 1974 to April 1977. The Shinobazu Pond was divided by the stroll ways into three parts, the Zoo part, Hasu Pond part and Boat Pond part where hired boats were floated between 9:00 to 17:00. In the Zoo part, the daily feeding for wild ducks has been continued since 1954. The routine observations were carried out at 7:30 - 8:30 in the morning.
The results obtained were as follows:
1. An annual increasing of the wintering ducks was continually noticed as shown in Fig. 1. The main reason for this fact was seems to be in fanciers' feeding at early morning in Boat Pond and in the daily feeding in the Zoo part.
2. Throughout the observation periods, 14 species including two rare species in Japan, the American Wigeon and the Ring-necked Duck (the first record in Japan; FUKUDA, 1977) were observed (Table 1). In their population, the Pochard and the Tufted Duck increased greatly, the Mandarin Duck decreased gradually and the others did not change generally.
3. On the sex ratio, the males were usually predominent over the females in most species (Pintal, Mallard, Teal, Wigeon, Shoveler and Pochard) except the Tufted Duck (Table 2).
4. On the distribution of the ducks in the Shinobazu Pond, the Pintail and Wigeon increased in Boat Pond. Nevertheless of the remarkable increase of the Pochard and Tufted Duck, their numbers in Boat Pond decreased gradually (Fig. 4).
5. The movement of the ducks in the three parts of the Shinobazu Pond might depend on the feeding time (at 9:30 - 10:00 and 15:30 - 16:00). And it seems to be their daily repeated behaviour that they moved to the Zoo part in the daytime and returned to the floating area by the next morning.
6. From the annual observations, the constituent members of the wintering flock were accepted as inconstant members to some extent, and they had a tendency to lose their regular habitual situation in the Shinobazu Pond.