Trends in wader populations in the East Atlantic flyway as shown by numbers of autumn migrants in W Denmark, 1964–2003

Many wader populations are estimated to be declining. These estimates are mainly based on mid-winter counts, where much bias may occur in the form of varying geographical coverage, varying methods, birds changing wintering sites from year to year or over longer time, and counting error. Other trend estimates derive from breeding area data, which often are very uncertain due to the extreme geographical dispersal of most breeding distributions. Here we present data on 17 wader species passing Blåvandshuk in W Denmark on autumn migration during a 40-year period. Visible migration of birds including waders is highly sensitive to differing weather conditions from year to year, but the data are unaffected by the biases mentioned for mid-winter counts. The populations involved mainly originate from north boreal and arctic breeding sites from Greenland/Canada in the west to central Siberia in the east. One species stands out showing significantly decreasing trends, namely Eurasian Oystercatcher Haematopus ostralegus. The Eurasian Oystercatchers passing Blåvandshuk mainly originate from Norwegian breeding grounds, and the decrease corresponds to decreases on the wintering  grounds associated with overexploitation of bivalve stocks. Most other species showed relatively stable, fluctuating or increasing trends, and according to our data, most north boreal and arctic wader populations on the East Atlantic flyway seem to have been doing well during the last 40 years.