Wesołowski T., Głażewska E., Głażewski L., Hejnowicz E., Nawrocka B., Nawrocki P., Okońska K. 1985. Size, habitat distribution and site turnover of gull and tern colonies on the middle Vistula. Acta Ornithologica 21: 46-67.

The study was carried out in the years 1981-83 in an unchannelled segment, almost 400 km long, of the Vistula. Parts of the river stretch under study were checked during one to three seasons. In the stretch there occur the largest relic „river\" populations of Sterna hirundo and S. albifrons in central Europe. The breeding of gulls on the Vistula is relatively new, dating from the 60s. The data analysed relate to both tern species, as well as to Larus canus and L. ridibundus. The largest Sterna albifrons colony consisted of 46 pairs, that of S. hirundo - 140 pairs, Larus canus - about 500 pairs and L. ridibundus - 1500 pairs. In all the species small colonies predominated, but most of the population nested in larger colonies. In Larus canus and Sterna hirundo the frequency of occurence of each of the colony size classes varied between habitats and river portions. Sterna albifrons nested almost exclusively on bare sand, whereas Larus canus was a species occupying the widest spectrum of habitats. The largest proportion (70%) of structurally suitable islands was used for nesting by Sterna hirundo, and the smallest (15%) by Larus ridibundus. In all the species, except Sterna albifrons, a higher turnover rate was found for small then for large colonies. The tendency to nest near the colony of another species was most marked in Sterna albifrons, over 90% of the colonies of this species was in the immediate vicinity of S. hirundo colonies.