Spring arrivals of migrant waders in Iceland in the 20th century

Abstract

Records of first sightings of Icelandic‐breeding waders and high‐Arctic passage migrants have been made in most parts of Iceland since 1902. Two sets of records of first sightings are used here to analyse temporal changes in arrival dates during the 20th century and the effects of weather conditions. First sightings became earlier in the first half of the 20th century, as local spring temperatures increased. They ceased to do so after 1960, when temperatures were decreasing slightly, though the associations between arrival dates and annual temperatures were weak. In years with more than five records for a species, the earliest sightings were 5–9 days before the median dates of all first sightings. Though earliest sightings were delayed in cool Icelandic springs, those median dates showed little correlation with local spring temperatures. Six species arrived later when the winter or spring values of the North Atlantic Oscillation (NAO) were high, but seven species showed no significant associations with the winter NAO. Sightings tended to be later in springs in which westerly or cyclonic systems were prevalent over Ireland and Scotland. First sightings in Iceland were substantially later than in the Outer Hebrides, though in closer synchrony with the peaks of passage there than with arrival and passage dates in Shetland and north Norway. Sustained observations at a few key sites should be useful in tracking the responses of waders to variations in climate and other environmental changes.