Mihaela Ilieva, Pavel Zehtindjiev
Institute of Zoology, Bulgarian Academy of Sciences, Bulgaria
michaela_ilieva@yahoo.com
Realization of bird migration is known to depend on weather situation
as well as physiological condition of the individuals. Using two types of cages,
Emlen funnels and Busse cages, three species of trans-Saharan migrants: the
Sedge Warbler (Acrocephalus schoenobaenus), Great Reed Warbler (A.
arundinaceus) and Willow Warbler (Phylloscopus trochilus) were tested in order
to reveal the influence of meteorological factors and physiological condition on
their orientation. During the autumns of 2001 - 2004, we performed daytime
and night orientation experiments at Kalimok Field Station (41o00?N 26o26?E, NE
Bulgaria) with 1074 birds of these species. For the three analyzed factors ?
cloudiness, fat level and breast muscle size, clear tendencies, typical for the all
species studied were not registered. For the Sedge Warbler and Willow Warbler
testing under clear sky during the day leads to increase of NW direction. Birds
from the same species with high fat reserves show more southern orientation.
Increase in NW direction was registered for great reed warblers with increase of
fat level and muscle size. In night tests decrease of seasonal inappropriate
directions for willow warblers and increase of southern directions for sedge
warblers was observed under clear sky. Sedge warblers with high fat and muscle
score showed more southern directions. The results obtained indicate difference
in the factors? influence, depending on the species and testing time ? day or
night.




