SPAANS B, M BRUGGE, A DEKINGA, H HORN, L VAN KOOTEN & T PIERSMA (2009) Space use of Red Knots Calidris canutus in the utch Wadden Sea. LIMOSA 82 (3): 113-121.

Many bird species are site-faithful, not only to breeding sites but also to the areas used during migration and wintering. For Red Knots we already knew that they use very large home-ranges in the Wadden Sea (800 km2, equivalent to half the Dutch part of this area), whereas they have very small home-ranges (10-15 km2) in their wintering area on the Banc d'Arguin in Mauritania. Here, the main question is whether Red Knots restrict themselves to half the Dutch Wadden Sea or maybe also move between the western (West) and the eastern parts (East) of this area (Fig. 1) and if so, to which extent? We analysed resighting data from a long-term colour-ringing project on this species (Tab. 1), and applied radiotransmitters on 20 Red Knots in West and 20 in East after erecting 11 automatic receiving stations throughout the Wadden Sea (Fig. 1) to investigate the exchange between West and East within a period of two months. Many Knots caught in West ('West-Knots') were seen in East and vice versa, but the fraction of West-Knots seen in West was 2.8 times higher than the fraction of East- Knots resighted in West. In the same way, the fraction East-Knots resighted in East was 2.1 times larger than the fraction of West-Knots seen in East. So there was much exchange between the two areas but there is also site fidelity to the catching area in subsequent years. The fraction Knots resighted in important Red Knot areas abroad did not differ much between the two catching areas (Tab. 3).
      The telemetry experiment showed that East-Knots moved to West in the course of the autumn while West- Knots stayed within West, though they used a large area there (Fig. 2). Half of the East-Knots visited West more than once during a period of one month and one bird moved at least seven times between these areas. It is likely that this bird made use of tailwinds to make these flights (Tab. 5). The data presented support the known existence of large home-ranges in this species in the temperate zone and show that part of the individuals have even larger ranges than hitherto estimated. The main reason for this seems the unpredictable presence and/or availability of food resources (mainly small shellfish). It is suggested that the higher average temperatures in winter in West than in East and the smaller migration distance from West to alternative wintering areas in Britain could be the reasons why many East Knots move to West in the course of the autumn.

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