Michał Polakowski, Monika Broniszewska, Artur Goławski
Ornis Polonica 2014, 55: 279–289
https://doi.org/10.12657/ornis.2014.4.4
Abstract: We compared results of counts of non-breeding ducks (including mergansers) during their spring migration in the southern part of the Biebrza river valley conducted in 2013 and 2014. Birds were simultaneously counted with two methods: from the river bank and from the boat. There is a limited access to the valley of Biebrza River between Osowiec and Łoje Awissa villages, while between Łoje Awissa and the mouth of the river, the western bank is easily accessible. The observations from a boat between Osowiec and Łoje-Awissa revealed the presence of 4.5 times more birds compared to the river bank observations. Likewise, between Łoje Awissa and the river mouth the difference observed amounted to 1.7 times more birds in favour of counts from the boat. The number of species recorded with the two methods was comparable in both sections of the river. However, the percentage share of species differed considerably between the compared methods in the upper section, between Osowiec and Łoje-Awissa. On the other hand, between Łoje-Awissa and the river mouth, no differences were noticed in the domination structure of the bird groups counted using both techniques. In the case of large river valleys characterized by wide floodplains and hindered access from riverbanks, it is strongly recommended to use boat in order to estimate the number of small-sized waterbirds.
Keywords: Anatinae, Biebrza Valley, non-breeding ducks, spring migration
