We are doing research on a number of colonies of the Dalmatian and the Great White pelican trying to understand why some areas, apparantly suitable for nesting, lying adjacent to nesting units remain unoccupied. Is this due to some physical features of the habitat thjat we cannot directly perceive? is it because of some obscure social reasons? are there socially unacceptable sub-areas of the colony space? all this is dirctly related to our need to say whether a particular colony is limited by availability of nesting sites or not, which is a crucial question to answer for contributing ot our understanding of the ecology and the conservation fo the species.