Detection of Bald Eagles during aerial surveys in Prince William Sound, Alaska

Bald Eagles (Haliaeetus leucocephalus) are often counted by aerial surveys but, because some birds are not detected, this approach provides only an in dex to population size. We estimated detection rates for Bald Eagles during fixed-wing aerial surveys in Prince William Sound, Alaska to extrapolate t he index to an estimate of the total population of Bald Eagles in Prince Wi lliam Sound. Using a modified Petersen estimate and independent front and b ack seat observers, we estimated that we detected 79% and 51% of observable adult and immature eagles, respectively. Using data from a radiotelemetry study, we also estimated that 21% of adult eagles were unavailable for dete ction because they were in locations not visible to airborne observers foll owing the shoreline at tree-top level. Combining both perception and availa bility biases, 62% of adult eagles was seen (visibility, correction factor of 1.6). Detection rates were similar between a Cessna 185 and a turbine De Havilland Beaver aircraft. We believe these detection rates are generally a pplicable to Bald Eagles in the coniferous coastal forests from Washington to Alaska, but encourage collection of similar data in future surveys to en able estimates of site-specific detection rates.