• Hutchinson, Alan
  University of Maine Graduate School
  

The cost, and reliability of visual estimates from ground level, visual estimates from aircraft, counts from photographs and direct nest counts, as techniques for estimating numbers of colonial nesting seabirds, were determined and compared. Disturbance to the nesting colony from inventorying and the seasonal turning of inventories were also investigated. Numbers of nesting double-crested cormorants (Phaloerocorau auritus), herring gulls (Laras argentatus and great black-backed gulls (farus marinus) were estimated, using each technique, on 14 coastal islands in Hancock county, Maine during the nesting season of 1978. Confidence intervals calculated for each technique showed that direct nest counts gave the most reliable estimate of nesting populations for both gulls and cormorants, followed by counts from photographs. Visual estimates from the ground or from aircraft were least reliable. Direct nest counts, however, were six times more costly than any other technique. Aerial estimates were least costly followed by photo counts and ground-level estimates.