Evaluation of aerial surveys of ptarmigan Lagopus species.
A study was conducted during 1990-96 to evaluate the reliability of aerial surveys to monitor trends in the breeding population density of ptarmigan Lagopus spp. over large areas (>30 km2) in south-western Yukon, Canada. The area studied was boreal forest in the subalpine region of Kluane, and Salix spp., Betula glandulosa and Picea glauca provided the most cover for the birds. Aerial surveys provided repeatable indices of density, and aerial indices of density were positively and linearly related to density between areas within the same year. However, aerial indices of density were not positively related to density between years because the aerial index was lower in 1996 than in 1995, while in fact the density of ptarmigan increased. It is suggested that this may be due to a reduction in the flushing response of ptarmigan in 1996. It is concluded that wildlife managers against a possible inter-year variation in the number of animals that can be seen from the air when conducting aerial surveys.