ABSTRACT
Starlings roost mainly on vegetation such as trees and reeds and sometimes on buildings and other man-made objects. It is difficult to estimate the size of feeding flocks, where individual distance is very variable, in contrast to flying, preroosting, or roosting flocks. Sophisticated equipment is needed for counting flying birds even during the daytime and for counting roosting birds at night. Individual distance between birds is relatively small, hence density is easily calculated and the area occupied by the birds may be measured. The total number of birds in a preroost is calculated by multiplying density by area. Counting flying birds can be done by determining their size flock and density by a technique that uses standard photogrammetric methods for determining the three coordinate positions of birds in flocks from stereoscopic pairs of simultaneously exposed photographs. The results enable the calculation of both density and size of the flocks and the number of birds in them.
