Different migration strategies used by two inland wader species during autumn migration, case of Wood Sandpiper Tringa glareola and Common Snipe Gallinago gallinago

Abstract

Waders generally follow two alternative strategies. The "B-strategy" or "energy minimization" strategy is to initiate migration late in the season, start moulting at the breeding grounds and migrate slowly in small steps, whereas the "S-strategy" or "time minimization" is to migrate immediately after the end of the breeding period and moult on the wintering grounds after a migration with only a few stopover sites. We studied Wood Sandpipers Tringa glareola and Common Snipes Gallinago gallinago at the Polish Jeziorsko reservoir. Adult and juvenile Wood Sandpipers migrate during different periods, and showed no signs of moult. In contrast, both age groups of Common Snipe migrate during the same period, and up to 30% of ringed adult Common Snipes had started their post-breeding moult at the reservoir. Wood Sandpipers stayed 4-5 days at the reservoir, where they fattened at a rate of 1.15 g/day (which was positively correlated with their length of stay, r = 0.21), and left with 21% of fat (% of LBM), allowing them to cover distances exceeding 2,500 km (which enables them to reach the coast of the Mediterranean Sea). In contrast, Common Snipes stayed 11 days, fattening 0.3 g/day, and left the reservoir independently of their fat reserve. Common Snipes stored a significantly smaller fat reserve than Wood Sandpipers, and their reserve was predicted to allow maximally 1,500 km of constant flight. Our findings support the hypothesis that, under common feeding conditions at Jeziorsko reservoir, Common Snipes behave according to the energy minimization strategy whereas Wood Sandpipers use a time minimization strategy.