Evaluation of Aerial Transect Surveys of Mottled Ducks

Abstract

Aerial counts of mottled ducks (Anas fulvlgula maculosil) along random transects were used to establish population Indices In Louisiana and southeastern Texas. Samples were stratified by habitat type, and replicated flights were made In February 1985, August 1985, and February 1986 to count mottled duck, occurring In strips on both sides of the air· craft. The August 1985 population Index was 173% greater than the Index of February 1985 and consistent with a post-breedlng season Increase In mottled duck numbers. The August survey also had a higher coefficient of variation, that probably resulted from the presence of large flocks of mottled ducks at that time of the year. The population Index Increased from 16,793 in February 1985 to 34,022 in February 1986. Other species of ducks were abundant In February, and observers had to differentiate between those species and mottled ducks. The mottled duck Index was greater in 100-m strips than 200-m strips, but the coefficients of variation were similar. The 100-m strip Is recommended for surveys made In February, because of the difficulty of differentiating mottled duck from other species at distances >100m.