Nest trees should be individually marked and numbers of nests recorded. This should be done after the young begin to hatch, both to help locate nests from the debris on the ground near the trees, and to reduce disturbance at the site. Because of their Endangered status, effort should be made to estimate rather precisely the number of nests in a colony. This can sometimes be done from fixed-wing aircraft, but usually ground censuses are needed. Simply returning to previously-used sites may result in a bias in trends.
Most heronries have several or more species.
Because the eggs of many species are indistinguishable, estimating exact numbers of nests can be difficult. For larger colonies, we recommend that several censusers enter the colony to flush birds, while 2 or more observers remain outside to estimate numbers by species. It may be necessary to divide up the species by observer. On average, we estimate one adult equals one nest for most wader species. If a state is so large that a complete inventory cannot be achieved in a given year, it is best to conduct a census of the large colonies at a minimum.