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Different spatial distributions Of food abundance and predators may urge birds to make a trade-off between food intake and danger. Such a trade-off might be solved in different ways in migrant birds that either follow a time-minimizing or energy-minimizing strategy; these strategies have been assigned to two subspecies of Bar-tailed Godwits Limosa lapponica that use the European Wadden Sea during northward migration. At the study area on Terschelling, we recorded feeding site selection, time budgets and intake rates (prey/min) in the period that both lapponica (energy minimizer) and taymyrensis (time minimizer) subspecies were present (late April till the end of May 2007). Prey availability (number of prey/m(2)) was negatively correlated to the distance from cover. Based on resightings of colour-ringed Bar-tailed Godwits, taymyrensis was foraging closer to cover, and for a higher proportion of time than lapponica (67% vs. 33%). During the high tide period taymyrensis was also foraging on inland coastal meadows. Moreover, taymyrensis was more vigilant than lapponica, whereas lapponica showed more resting and preening behaviour. Lapponica had a higher instantaneous intake rate, but taymyrensis had a higher overall intake rate and the birds were more successful in taking larger prey items than lapponica. Supposedly, due to the increased foraging time and additional foraging on the inland meadows, the time-minimizing taymyrensis achieved a higher fuel deposition rate than lapponica. Taymyrensis shifted towards food-rich areas, apparently accepting higher predation risks, whereas energy-minimizing lapponica avoided predation danger by foraging further from cover.

In 1999 and 2000, 45 Bar-tailed Godwits Limosa lapponica were supplied with radio-transmitters during spring staging on the island Texel in the western Wadden Sea. With the use of Automatic Radio Tracking Stations (ARTS) on Texel and in south Sweden, and hand-held receivers on Texel, it was possible to follow the later part of the stopover period on Texel for 34 birds (76%) and the passage over south Sweden for 26 birds (58%). Thus, the method of automatic tracking of overflying migrating shorebirds works successfully where the migration corridor is narrow and predictable, as in the case with late spring shorebird migration from the Wadden Sea towards arctic Russia. The timing of departure from Texel and passage over south Sweden of radio-marked birds, with median dates of 30 May and 2 June respectively, were in agreement with published data on the spring migration of Siberian-breeding Bar-tailed Godwits L. l. taymyrensis. The individual variation in migration dates was larger than expected, with birds passing south Sweden between 25 May and 10 June, indicating that the time-window for departure might be broader than previously thought. There was no clear difference between males and females in timing of migration. The time difference between departure from Texel and passage over south Sweden (average 3.3 days) indicates that most Bar-tailed Godwits do not embark on the long flight towards Siberia directly from the western Wadden Sea, but are more likely to stop in the more easterly portion of the Wadden Sea before the final take-off. This pattern is similar to what has been found in other shorebirds and geese (e.g. Red Knots Calidris cantus and Dark-bellied Brent Geese Branta bernicla) migrating along the same route.

In 1999 and 2000, 45 Bar-tailed Godwits Limosa lapponica were supplied with radio-transmitters during spring staging on the island Texel in the western Wadden Sea. With the use of Automatic Radio Tracking Stations (ARTS) on Texel and in south Sweden, and hand-held receivers on Texel, it was possible to follow the later part of the stopover period on Texel for 34 birds (76%) and the passage over south Sweden for 26 birds (58%). Thus, the method of automatic tracking of overflying migrating shorebirds works successfully where the migration corridor is narrow and predictable, as in the case with late spring shorebird migration from the Wadden Sea towards arctic Russia. The timing of departure from Texel and passage over south Sweden of radio-marked birds, with median dates of 30 May and 2 June respectively, were in agreement with published data on the spring migration of Siberian-breeding Bar-tailed Godwits L. l. taymyrensis. The individual variation in migration dates was larger than expected, with birds passing south Sweden between 25 May and 10 June, indicating that the time-window for departure might be broader than previously thought. There was no clear difference between males and females in timing of migration. The time difference between departure from Texel and passage over south Sweden (average 3.3 days) indicates that most Bar-tailed Godwits do not embark on the long flight towards Siberia directly from the western Wadden Sea, but are more likely to stop in the more easterly portion of the Wadden Sea before the final take-off. This pattern is similar to what has been found in other shorebirds and geese (e.g. Red Knots Calidris cantus and Dark-bellied Brent Geese Branta bernicla) migrating along the same route.