Black-headed Gull roost

I was observing Black-headed Gulls at roost that evening in Maribor (close to the city-centre). Gulls are sleeping not far away from the bank of the Drava river so counting them is not difficult. I could see 908 BHGs and only 1 Common Gull. It is good to know gulls are very numerous because I will try my luck at reading ringed birds.

                                          Black-headed Gulls