Nocturnal Migration in the Tataka Area, Yushan National Park, Taiwan in Autumn 2014

Abstract

Detecting different bird species requires different and appropriate surveying methods. We tested a new detection method for the Tataka Area in Yushan National Park, Taiwan, which is an important alpine stopover site for migratory land-birds. Numerous migrant species have previously been reported from this area during bird counts and banding operations. However, these traditional survey methods are incapable of detecting nocturnal migrants. Therefore, we applied acoustic monitoring devices to survey the flight calls of nocturnal migrants in the Tataka Area in order to identify the species and estimate their detection rate. We set up acoustic recorders at five recording stations twice a month during September, October and November, and once in December 2014. We identified 18 nocturnal migrant taxa from 801 hours of recordings. The Black-crowned Night Heron Nycticorax nycticorax was the most frequently recorded species, followed by thrushes (Turdus spp.) and the Brown Shrike Lanius cristatus. Passages of nocturnal migrants occurred during every hour of the night, but with a significantly higher detection rate during the period from 2000 to 2300. Detection rates also varied significantly among months and recording stations. Significantly higher detection rates were recorded in September and October than in November and December. The recording station on a ridge detected significantly fewer birds than the other four recording stations situated in or near valleys. This suggests that nocturnal migrants use lower-lying stream valleys in order to pass over mountain ridges at the lowest possible point. This study provides the first evidence to demonstrate that, besides landbird migrants, many shorebird species and even kingfishers migrate through alpine areas at night when they pass over Taiwan Island during autumn migration.