 The call is mostly uttered in flight and is a harsh " tsak tsak tsuk " . The same sound , but softer , is made more conversationally when individuals gather in trees . When angry or alarmed they emit various warning sounds reminiscent of the mistle thrush ( Turdus viscivorous ) . The male has a rather feeble song that he sings in the breeding season . It is a mixture of a few phrases like those of the common blackbird ( Turdus merula ) interspersed with whistles , guttural squeaks and call notes . This is sung on the wing and also from a tree and a subdued version of this song with more warbling notes is sung by a group of birds at communal roosts . 
