Spring Migration of Chinese Goshawks (Accipiter soloensis) in Taiwan

Abstract

Little is known about the abundance and distribution of Chinese Goshawks (Accipiter soloensis) during spring migration along the Western Pacific flyway around Taiwan. This species is the most numerous migratory raptor in East Asia. In April 2004, we employed weather radar at Kenting and Chiku to study the spatial and temporal distribution and flying behavior of migrants in the Taiwan area. Goshawk flocks migrating across Luzon Strait toward Taiwan (n = 193) averaged 3.1 km in length (SD = 3.41, range 1.0–27.5 km) and 0.7 km in width (SD = 0.30, range 0.3–2.5 km). Using a regression model relating bird numbers to the reflectivity of radar images, we estimated that at least 225 935 Chinese Goshawks passed through the study area during 5 d in the month of April. Flocks crossing the Luzon Strait approached the Hengchun Peninsula, at the southern tip of Taiwan, along several inland and offshore routes, making it difficult to obtain accurate and complete observations from the ground. Farther north at Chiku, we used radar imaging to estimate 150 619 northbound migrants, 67% of the number detected by the Kenting radar. Of these, 24% bypassed Taiwan and flew nonstop to mainland China via the Pescadores, located off the west coast of Taiwan. Another 55% flew over the southern end of Taiwan and then across the Taiwan Strait to the mainland. The remaining 21% continued north over Taiwan after spending up to 2 d in the central mountains of Taiwan. This likely explains why relatively small numbers of goshawks are observed in central and northern Taiwan. Chinese Goshawks flew more slowly and higher over land than over water, and their ground speed increased with favorable winds.