We surveyed a heronry for 16 years to study nest site selection in relation to bird species presence and vegetation structure. Black-crowned Night Heron (Nycticorax nycticorax) was the most abundant species, while Little Egret (Egretta garzetta) and Grey Heron (Ardea cinerea) increased only in the last years. In a first phase, Black-crowned Night Herons selected tall Black Locusts (Robinia pseudoacacia) for nesting. Later they moved into the understory, selecting Hawthorn (Crataegus monogyna) and Black Elderberry (Sambucus nigra), while the higher canopy was used by Grey Herons. The result was a stratification of nests of different species. Considering the succession in use of different forest strata by the medium-sized heron species and years of Grey Heron arrival, it is likely that the forest structure more than competition between species influenced nest site selection in this heronry.