Estimating the size of breeding populations of colonial nesting wading birds is a priority for waterbird management but locating colonies can be difficult. Existing methodologies to locate wading bird colonies require use of airplanes and/or a systematic search of likely colony locations on the landscape. This study describes the use of vanishing bearings of Great Blue Herons (Ardea herodias) as they depart coastal foraging sites to determine the number and location of associated breeding colonies. In 2002, frequency analysis of the vanishing bearings identified 23 modes at ten sites while in 2003, 29 modes at 15 sites were identified. Of these modes, about one-half (twelve in 2002 and 15 in 2003) were associated with a known colony. Groupings of vanishing bearings unassociated with known colonies prompted searches for unknown colonies. Searches in 2002 and 2003 found three colonies missed during routine colony inventories using information from the public. Intensive searches in 2004 and 2005 at foraging sites where large colonies had previously abandoned located four previously unknown colonies. These results give confidence that all colonies associated with known foraging sites can be located using this method.
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Vol. 29 • No. 2