Ardea
Official journal of the Netherlands Ornithologists' Union

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van Brederode N.E. & Roersma H.J. (2020) Turnover, passage population size and flight range of juvenile Ruddy Turnstones at a non-estuarine staging site in The Netherlands. ARDEA 108 (2): 213-222
For five consecutive years (2001–2005), during a one-month period in August–September, we studied the turnover of juvenile Ruddy Turnstones Arenaria interpres at a tidal area along the Dutch coast, by colour-marking cohorts of migrants. Taking turnover into account revealed that 1.8–2.4 times as many juvenile birds used the area during their southward migration, compared to the numbers based on maximum counts. This larger estimate amounts to 35% of the number at which the 1% criterion of the Ramsar Convention is met, whereupon a wetland is designated as internationally important, with significant implications for conservation commitments. Presuming adult birds had the same turnover factor, adult birds contributed almost 70% to the 1% criterion during the same period. Autumn migration of juvenile Ruddy Turnstones was rapid, with more than 50% of individuals leaving within 4 days (95%-CI: 3.4–4.6). The mean mass at departure, as derived from median staging duration and mean body mass gain from recaptured birds (1.1 g/d), was 104.3 g (±10.3 SD). The mean potential flight range as calculated using the aerodynamic approach by Pennycuick was 1981 km (±717 SD), which suggests that juvenile birds that leave the area can cover short to medium distances at most. The fuel loads are sufficient to reach one of the four key wintering sites along the coast of France, but not the Banc d’Arguin in Mauretania, which is the first key wintering site in West Africa. By early October, 80% of the birds had left the study area. Our study shows the importance of a small tidal area during autumn migration and raises the question of whether a considerable number of comparable small stopover sites along the coast of Western Europe and West Africa are needed. More attention to the designation and the protection of such sites and the achievement of a network would have the potential to greatly support juvenile birds on their first journey south.


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