NYBC Taiwan is a citizen science project which aim to monitor the status and trends of wintering birds of Taiwan and surrounding islands. It was launched by CWBF, Wild Bird Society of Taipei (WBST), Kaohsiung Wild Bird Society (KWBS) and ESRI in December 2013 (Lin et al., 2015a; Lin et al., 2015b; Lin et al., 2017a; Lin et al., 2017b).

The monitoring methods of NYBC Taiwan are followed the fundamental rules of Christmas Bird Count. During the 23 days from mid-December to early January (the middle date is January 1st), a volunteer team chose a consecutive 24 hours to count the birds within a circle sample area which radius is three kilometers. Bird species, abundance, location of route or observation, date, start time, end time, party size, survey methods and weather were recorded. The bird survey methods including line transect (Burnham et al., 1980), counting flocks (Bibby et al., 1992), area search (Ambroses 1989) and additional records. The number of circle sampling areas, volunteers, species recorded and individuals counted of NYBC Taiwan from 2014 to 2018 are listed on the Table 2. We analyzed the five-year trend of the migratory waterbeds by rtrim package of R 3.5.1 (R Core Team 2012).

The population of Common Teal (Anas crecca, p < 0.01), Ruddy Turnstone (Arenaria interpres, p < 0.01), Sanderling (Calidris alba, p < 0.05), and Dunlin (Calidris alpina, p < 0.05) decreased significantly (Fig 3). Our datasets are opened on the open database of the Environment Protection Administration of Taiwan and published as an annual report every year (e.g. Lin et al., 2017b). They provide valuable information about the distribution and community composition of the avifauna in the winter of Taiwan. These data have been share with national and international organizations, such as the Ministry of Interior and the Wetland International for International Waterbird Census