Summary
Bird
migration studies are sparse in the Caucasus region, but have received
more interest in recent years. To date, these studies have focused on
diurnal migration and no information about nocturnal bird migration is
available from this region. Therefore, nocturnal bird migration in the
Besh Barmag bottleneck (Azerbaijan) was acoustically analysed on the
basis of 1,464 h 44 min of sound recordings cost-efficiently obtained
with an autonomously operating recorder and an omnidirectional
microphone between sunset and sunrise on 63 nights in autumn 2011 and 67
nights in spring 2012. In total, 88,455 calls of 106 migrating species
were detected. Of these, 2,172 calls could not be identified due to
recording deficiencies or imperfect familiarity with some of the
vocalisations and may involve as many as 20 species. The calls and songs
of another 13 non-migratory species were not counted. Due to
organisational or technical constraints some nights in the study periods
could not be analysed and so the ensuing data gaps were repaired by
interpolation, resulting in an estimated total of 108,986 calls in
autumn 2011 and 33,348 calls in spring 2012. In both seasons the most
vocally productive and species-rich phase was civil morning twilight,
containing as it does the onset of diurnal migration. In autumn 2011,
54.7% of the recorded calls occurred in civil evening and morning
twilight and 68.8% in spring 2012. But species and call numbers were
also high in the darkest twilight and night phases. The interpretation
of the data is, however, partly conjectural and any future access to
truly reliable information on migration densities is conceivable only
through radar studies.
The supplementary materials are online free available.
Find the paper here: https://doi.org/10.1017/S0959270917000454
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