Studies on the Behavior of Wintering Geese

I.Numbers of Geese wintering at Lake Izunuma

Abstract

(1) The authors studied the population size and change of wild geese wintering and roosting at Lake Izunuma (Fig.1), Miyagi Pref., northern Honshu, for seven years from 1971 to 1977.Monthly counts of bird number were made at daybreak when flocks of geese fly out of Lake Izunuma to feeding places. In addition, the numbers of geese roosting at the lake or feeding at paddy fields were counted during the daytime 3 to 4 times a month.
(2) The wintering geese at Lake Izunuma consist chiefly of the White-fronted Goose (Anser albifrons) and the Bean Goose (A. fabalis). The Lesser White-fronted Goose (A. erythropus), Lesser Snow Goose (A. caerulescens), Aleutian Canada Goose (Branta canadensis leucopareia) and Brent Goose (Branta bernicla) are rare or accidental visitors. In 1972 there were about 3, 000 White-fronted Geese and 200 Bean Geese. In spite of deterioration of the natural environment surrounding Lake Izunuma, they increased to 5, 600 and 1, 400 respectively in the following five years (Fig.4). The reason for the increase of the population of geese may be attributed to the prohibition of hunting of wild geese in Japan in 1971.
(3) Seasonal changes of numbers of the wild geese wintering at Lake Izunuma were shown in Figs.3, 5 and 8. In these monthly-peak-number graphs, there are 'cap' and 'two-peak' types (Fig.3). The graph of cap type shows an ordinary pattern of population change of wild geese at Lake Izunuma during one wintering period, i.e., wintering geese arrive in a small number in late September, increase to a large number in October, reach to a peak number in November or December, begin to decrease in late January, and then depart in February or March. The graph of two-peak type indicates that wintering geese take a temporary refuge in the south when paddy fields are covered with thick snow for a period of 30 days or more. They returned to roost at Lake Izunuma when the snow in paddy fields melted.
(4) The monthly-peak-number graphs of the White-fronted Goose resemble that of total wintering geese, because the number of White-fronted Geese is 60-80 % of the total goose number.On the contrary, the numbers of Bean Geese increases to a peak in October and then reaches at maximum in December. Against snow, Bean Geese also take refuge in the south but they seem to be more resistant to snow and the extent of movements during the snowy periods is smaller.
(5) The wintering geese depart from Lake Izunuma in February or March regularly.In the year when there is not much snow, they usually leave in February and the monthly-peak-number graph becomes a cap type. When there is much snow, they leave in March and the monthly-peak-number graph resulted in a two-peak curve.