SEEN - SE European Bird Migration Network
The stopover durations of the Sedge Warbler (Acrocephalus schoenobaenus) during the autumn migration in the reedbeds of the western part of Ukraine

Oksana Zakala
Western-Ukrainian Ornithological Station, Zoological Museum of Ivan Franko National University in Lviv, Hrushevsky str. 4, Lviv 79005, Ukraine

The main elements of migration organization are length of flight bout, stopover duration and fuel deposition rate. On the way to the wintering areas birds interrupt their flight to add to fat reserves. At good stopover sites birds replenish energy reserves and use them during the next flight step. Many longdistance migrants seem to be under selective pressure to minimize time spent migrating (Schaub and Jenni 2001). The stopover duration is a very important factor determining speed of migration. Very little is known about stopover durations of small migrant birds. The research was carried out in the Western-Ukrainian Ornithological Station in the ?Cholgyni? reserve during August 1999-2002. The territory of reserve is 820 ha. Birds were caught in mist-nets in the reedbeds (totally 2147 birds) of the artificial pond every year in the same place. We used the capturerecapture analysis to estimate stopover duration of the most common species in reedbeds - the Sedge Warbler. There were 85 Sedge Warblers caught more than one time. In all four years only young birds were found in the recaptures, except 1999 where adult birds were also recaptured (0.55% of all caught birds), but only in the end of the July to the beginning of the August. The rates of the recaptured Sedge Warblers were 1.8-4.5 % in different years. The recapture rate is higher 6.4 % for 1999 when the catching started on 11th, July. In 1999 one adult bird stayed for 32 days: from the middle July to the middle August, and it dropped in body weight and fat reserves. Thus we suppose it must have been a breeding bird. The birds stayed on the reedbed territory for 1-15 days, most frequently for 1 day ? 28.8%, for 2 days ? 17.3%, for 3 ? 14.4%, for 4 ? 12.5%, for 5 ? 7.7%, for 6 ? 7.7%, for 7 ? 2.9%, 8 and more days ? 0.96% respectively. In the first two days after the first catching Sedge Warblers dropped in their weight and fat loads, during 3-8 days ? they were both increasing and decreasing in weight and fat loads. After 9 and more days Sedge Warblers gained to weight and the fat loads. The largest weight gain was 1 g per day, but there were some retraps in the same day that showed the maximum gain up to 0.33 g per one hour. Therefore we suppose that the research territory is an important stopover place for migrating Sedge Wablers.

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