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




