Seasonal trends in summer diet of the lapland longspur near Barrow Alaska USA

Contents of lapland longspur [Calcarius lapponicus] stomachs and esophagi were sampled near Barrow, Alaska [USA], from May-Aug. in 1969, 1971, 1972 and 1973. Data from stomach contents were corrected for differential digestion of prey items. Longspurs shifted seasonally from larval to adult arthropods and back to larvae, responding to changes in the abundance of these prey items. Seeds were a vital supplementary food in late May and Aug., when arthropods were scarce or inaccessible. One species of crane fly was the major dietary component for longspurs during June and July. Its high abundance and substantial dry weight per individual may contribute to the success of longspurs at Barrow. The diets of longspurs and 4 common shorebirds (Calidris spp.) at Barrow were similar in the range of prey items taken except for seeds and tenthredinid larvae. Their diets overlapped closely when feeding sites were restricted because of snow and surface water (chiefly at the beginning of the season) and when prey was abundant in early to mid-July. Competition is possible early in the season but unlikely in July when surface insects are very abundant. Habitat separation and the advantages of fringillid form apparently contribute to the success of longspors in a tundra community of insectivores dominated by shorebirds.