Habitat use and flight paths of geese and swans at Lake Jusan a spring migration stopover site, in Northern Japan before construction of a wind farm

Abstract

Lake Jusan, Northern Honshu, is a major stopover site for geese and swans during spring migration; however, a wind farm is scheduled to be construct in rice fields southeast of the lake. To understand both the habitat use and flight paths of geese and swans in the area before construction of the wind farm, we investigated the number of migratory waterfowl, their migration period, flight direction, flight path and altitude. Our four-year study found that 36, 726–115, 233 geese and 3,415–6,743 swans migrated via the lake every year. The geese began migrating before dawn and most of them flew to the north or northeast; intensive flight paths were observed above the rice fields and the river southeast of the lake. The swans migrated after dawn and most of them flew northeastwards along the river. Migratory geese and swans frequently flew at altitudes corresponding to the heights of wind turbine blades, while birds flying between roosting and foraging sites flew at the same height or lower. Research results suggest that there are three areas of concern: 1) collision risk (the huge number of migrant waterfowl using the area and correspondence between their flight heights and the blades of the wind turbines are cause for great concern after construction of the wind farm); 2) habitat loss and displacement (the wind farm is going to be constructed over rice fields that currently serve as an important foraging site for waterfowl); 3) increased flight costs (the large number of wind turbines to be placed southeast of Lake Jusan will likely lead to increased flight costs for waterfowl while they move between roosting and foraging sites and when migrating as they divert to avoid the turbines). To mitigate these concerns, future study is indispensable after the construction of the wind farm.