Nocturnal Migration in the Tataka Area, Yushan National Park, Taiwan in Autumn 2014
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Ornithol Sci 19: 135 – 144 (2020) ORIGINAL ARTICLE Nocturnal migration in the Tataka Area, Yushan National Park, Taiwan in autumn 2014 Chao-Chieh CHEN1,#, Jane-Chi WU2, Bruno Andreas WALTHER3 and Po-Jen CHIANG4 1 Department of Biomedical Science and Environmental Biology, Kaohsiung Medical University, 100, Shih- chuan 1st Rd., Sanmin District, Kaohsiung City, 807, Taiwan 2 Wild Bird Society of Pingtung County, 900, Taiwan 3 Department of Biological Sciences, National Sun Yat-sen University, Gushan District, Kaohsiung City, 804, Taiwan 4 Formosan Wild Sound Conservation Science Center Co., Ltd., 2F, 335, Yongmei Road, Yangmei District, Taoyuan City, 326, Taiwan ORNITHOLOGICAL Abstract Detecting different bird species requires different and appropriate sur- veying methods. We tested a new detection method for the Tataka Area in Yushan SCIENCE National Park, Taiwan, which is an important alpine stopover site for migratory land- © The Ornithological Society birds. Numerous migrant species have previously been reported from this area during of Japan 2020 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. Key words Acoustic monitoring, Nocturnal flight call, Stopover site, Transit migrants Nocturnal migrants are elusive and difficult to cohesion of migrating flocks of conspecifics because study. Although radar is a useful tool for detecting they usually migrate together in a widely dispersed migrating birds, it is usually unsatisfactory for iden- pattern at night (Hamilton 1962; Larkin & Szafoni tifying species (Farnsworth et al. 2004; Gagnon et al. 2008). Coordination of movements during migration 2010; Smith et al. 2014). However, some nocturnal might be another purpose of flight calls (Griffiths et migrants give flight calls while migrating at night al. 2016). Since these flight calls are species-spe- (Graber & Cochran 1959, 1960; Evans 1994). One cific, they can be used to identify nocturnal migrants presumed function of flight calls is to maintain the to species level (Graber 1968; Evans & Rosenberg 2000; Murray 2004, http://www.islandnet.com/~rpbo/ (Received 15 October 2019; Accepted 18 February 2020) acousticmonjjm.pdf; Evans 2005; Farnsworth & # Corresponding author, E-mail: [email protected] Lovette 2005). Graber and Cochran (1959, 1960) pio- 135 C.-C. CHEN et al. neered the study of flight calls of nocturnal migrants. important stopover site in Taiwan for autumn Later on, Evans (1994) used more advanced acousti- migrants from northern regions, such as Japan, cal devices to monitor the migration patterns of noc- Korea, northeastern China, and Siberia (Sar 1989; turnal migrants in North America. Nevertheless, it Hsieh 1995; Chen et al. 2009, 2010). Sar (1989) first was time consuming to transcribe the recorded data noticed that significant numbers of Grey-faced Buz- (Evans & Rosenberg 2000). Recently, the automatic zard-Eagle Butastur indicus, Chinese Sparrowhawk classification of flight calls for bioacoustics monitor- Accipiter soloensis, Brown Shrike Lanius cristatus, ing has been developed (Stowell & Plumbley 2014; and migratory warblers (especially Locustellidae) Salamon et al. 2016), and its application will promote passed through this alpine stopover site in autumn. the study of flight calls in the future. He also reported the spectacular nightly experience Since 2009, scientists have tried to compile a com- of a huge number of migrating Brown Shrikes fly- plete bird list for the Yushan National Park (YNP) ing into a lodge at Shihshan Station (Fig. 1). Later in central Taiwan. They showed that YNP contains on, Hsieh (1995) carried out banding operations all of Taiwan’s 29 endemic bird species as well as from 1992 to 1994 in nearby Zizhong (Fig. 1) and almost all resident bird species except those which captured more than 20 different species of transit occur exclusively in the lowland plains (Chen et migrants. In recent years, Chen et al. (2009, 2010) al. 2009, 2010, 2018; Chen & Liu 2011). However, and Chen and Liu (2011) conducted a 3-year survey it has been very difficult to determine the number of autumn migration and found 12 additional migrant of migrant species that actually appear in the park. species in the Tataka Area. Shorebirds were occa- After conducting ground surveys and banding opera- sionally heard calling overhead during the night, but tions, we realized that these traditional methods were have never been caught in mist nets (see Chen et al. applicable only for diurnal landbird migrants, but 2009, 2010). The aim of this study was to identify were ineffective for nocturnal migrants. Therefore, nocturnal migrants through acoustic monitoring and we applied acoustic monitoring to identify nocturnal to quantify their relative abundance during autumn migrants by their flight calls in 2014. migration in the Tataka Area. This is the first acoustic The Tataka Area (Fig. 1) is well known as an monitoring study designed for migrants in Taiwan, Fig. 1. Map of the Tataka Area and the location of our five recording stations. The double black line indicates the only major road in the area, while the thin black line represents the county border (which for most of the map traces the highest part of the east-west ridge). Yushan National Park is indicated in green. The insert shows the location of our study site within Taiwan. 136 Nocturnal migrants in Taiwan and is possibly the first of its kind in eastern Asia. net websites such as Macaulay Library (2014, https:// www.macaulaylibrary.org/) and Xeno-canto (2014, https://www.xeno-canto.org/). After all the recorded MATERIALS AND METHODS files had been transcribed into an EXCEL worksheet, The study area is located along the New Central we tallied the number of species recorded per hour Cross-Island Highway between Zizhong (23°29′02″N, for all sampling periods. The number of migrant 120°49′49″E, 2310 m, a.s.l.) and the Tataka Saddle species (or species richness) detected per hour was (23°28′32″N, 120°54′00″E, 2600 m, a.s.l; Fig. 1). then defined as the detection rate. For later statistical The Tataka Area is located on the west flank of the analysis (see ANOVA below), we further categorized highest peak in Taiwan, Yushan (or Mount Jade, 3,952 the night into four periods: early night (1700–2000); m a.s.l.) and is the logistical base (2,620 m a.s.l.) for late night (2000–2300); midnight (2300–0200); and climbing its peak. We selected five recording stations before dawn (0200–0600). The local times for sunset along the east-west highway at approximately equi- and sunrise were 1806–1715 and 0543–0633 dur- distant locations (mean straight line distance=1,988 ing the study period (11 September to 16 Decem- m) within the Tataka Area. This array was chosen ber; Central Weather Bureau of Taiwan 2014, https:// in the hope of avoiding double counting of migrants www.cwb.gov.tw/V8/C/K/astronomy_day.html). that mainly pass over in a north-south direction. We tested three hypotheses concerning the spa- Four out of the five recording stations were “near- tiotemporal distribution of nocturnal migrants, with saddle” locations, associated with a nearby saddle; detection rate as the response variable. The first null the remaining station was near a ridge at a “non- hypothesis was that the detection rate would be the saddle” location (Fig. 1). Migrants are more likely to same for the four different months of autumn migra- pass over saddle locations, thus we considered such tion. The second null hypothesis was that the detec- locations as “treatment sites.” In contrast, mountain tion rate would be the same for the four different ridges are more likely to present barriers to migrants, nighttime periods. The third null hypothesis was that therefore we considered the non-saddle location to be the detection rate would be the same for the five a “control site” (see further details in Discussion). different recording stations. To test these hypothe- We conducted seven field trips during the autumn ses together, we conducted a Three-way Repeated migration of 2014, two per month during Septem- Measures ANOVA with “hour” as the sampling unit ber, October and November, and one in the middle (SAS software, version 9.4; SAS Institute Inc., Cary, of December. At each station, we set up one digital North Carolina). recorder (Sony, M10) before dusk and operated it throughout the night (recordings usually lasted from RESULTS 1700 until 0600). Each recorder was attached to a tree trunk or a roadside facility (e.g., traffic sign- We examined recordings from 14 nights at five post) at approximately 1.5 m in height.