Ducks change wintering patterns due to changing climate in the important wintering waters of the Odra River Estuary

Abstract

Some species of birds react to climate change by reducing the distance they travel during migration. The Odra River Estuary in the Baltic Sea is important for wintering waterfowl and is where we investigated how waterbirds respond to freezing surface waters. The most abundant birds here comprise two ecological groups: bottom-feeders and piscivores. Numbers of all bottom-feeders, but not piscivores, were negatively correlated with the presence of ice. With ongoing global warming, this area is increasing in importance for bottom-feeders and decreasing for piscivores. The maximum range of ice cover in the Baltic Sea has a weak and negative effect on both groups of birds. Five of the seven target species are bottom-feeders (Greater Scaup Aythya marila, Tufted Duck A. fuligula, Common Pochard A. ferina, Common Goldeneye Bucephala clangula and Eurasian Coot Fulica atra), and two are piscivores (Smew Mergellus albellus and Goosander Mergus merganser). Local changes at the level of particular species vary for different reasons. A local decline of the Common Pochard may simply be a consequence of its global decline. Climate change is responsible for some of the local changes in the study area, disproportionately favoring some duck species while being detrimental to others.

Long-term changes in the numbers of waterbirds at an important European wintering site

“…In north-western Poland, numbers of water birds as a group have increased over the last two decades. This situation can be explained by climate warming, because this phenomenon has been already demonstrated for some waterbird species wintering at these latitudes (Lehikoinen et al, 2013, Pavon-Jordan et al, 2015, Marchowski et al, 2017. The shifting boundaries of birds' ranges as a result of climate change may be variously manifested in the study area: numbers of some species are on the increase, others are decreasing.…”

“…with a maximum of 21,300. More advanced calculations, taking into account such predictors as the size of the entire flyway population and ice cover, showed a decreasing trend in 2002-2016(Marchowski et al, 2017. The probable decrease in abundance can be explained by the wintering grounds shifting farther east and north, where numbers have increased (Lehikoinen et al, 2013).…”

“…Looking at the individual species, the situation is much more complex than the overall pattern would suggest: the causes of changes in numbers can be quite different. Depending on the species, increases or decreases in number may have the same cause, or the same direction of change may have different causes (Marchowski et al, 2017).…”

“…The following way of listing species in the text (e.g. Marchowski et al, 2015Marchowski et al, , 2017, standard in ornithological publications, has been adopted: when the species name appears for the first time, the full English name is given along with the full scientific name (genus and species -in italics); whenever a species is referred to again in the text, the English name only is used.…”

“…The site monitored by ZTP is not accidental. The north-western part of Poland is one of the most important waterbird wintering areas in Europe (Skov et al, 2011), and the region is particularly important for species such as Greater Scaup Aythya marila (hereafter Scaup), Common Pochard Aythya ferina (hereafter Pochard), Goosander Mergus merganser and Smew Mergellus albellus (Marchowski et al, 2017. This article summarises the results of the monitoring of several key bird species and the changes in their numbers over a period of 17 years.…”