Common european frogs (Pelophylax kl. esculentus) the hybrid of the Pool frog (Pelophylax lessonae) and the Marsh frog (Pelophylax ridibundus) on tree trunk submersed in water, near Muilovcica village, Lonjsko Polje Nature Park, Ramsar Site, Sisack-Moslavina county, Slavonia region, Posavina area, Croatia, June 2009