I photographed this bird few days ago in central Croatia and I instantly called it "Siberian Chiffchaff". I tried to induce the voice with the playback, but there was too much noise of water and I couldn't hear any call. Now it came up that it might be the first Siberian Chiffchaff ever for Croatia. I know that without the call is almost impossible to tell for sure, but is there anybody that doesn't agree this is most likely a tristis??