Trends in the Autumn Passage Numbers of Arctic and Boreal Waders in W Denmark 1964–2017 as a Contribution to East Atlantic Flyway Population Trends

Abstract

On the East Atlantic Flyway, where mid-winter counts of waterbirds have taken place for half a century, there is still uncertainty about trends in the sizes of several wader populations. For example, extensive breeding bird monitoring in boreal Fennoscandia, long term monitoring of actively migrating (i.e. passing) birds, and mid-winter counts give conflicting results for a good number of species. In this paper we contribute with the results of 54 years of monitoring of actively migrating birds passing Blavandshuk on the west coast of Denmark and just north of the Wadden Sea each year during 30 June – 27 September. The dataset comprises 14,678 observation hours, and 14 wader species with a total of almost 1.5 million individuals migrating south that were selected for analysis. The vast majority of the birds recorded are adults, i.e. without the large annual fluctuations in juvenile numbers caused by year-to-year variations in breeding success. By combining monitoring results from mid-winter counts, the Fennoscandian breeding grounds and monitoring of passing birds in Denmark and Sweden, the overall picture is that most Arctic and boreal wader populations on the East Atlantic Flyway are thriving. Hence, 24–26 populations appear to have been stable, fluctuating or have shown long-term increases; however, one of these populations has shown a decline in recent years. In contrast, 8–10 populations show declines with one of these indicating some degree of recent recovery. Furthermore, two populations have unknown status.