Flight behaivour and collision mortality of waterbirds flying across electricity transmission lines adjacent to the Shortland Wetlands, Newcastle, NSW

Bird flight behaviour and collision mortality of waterbird species flying across 330kV electricity transmission lines situated adjacent to the Shortland Wetlands were investigated. The study was conducted over two breeding seasons (1990-91 and 1991-92) during the period of peak flight intensity, when large numbers of four egret species breed and large numbers of ibis roost within the Shortland Wetlands. The study involved observations of flight behaviour of birds flying in the vicinity of, or crossing the transmission lines, and ground searches for dead birds. A total of 77 collisions with the transimission lines were observed during the study. The mean observed collision rate was 0.53 per 1000 flights. The mean mortality rate from observed collisions was low, 0.004 per 1000 flights. The mortality rate that was inferred from the number of dead or injured waterbirds located during ground searches was an order of magnitude higher, 0.04 mortalities per 1000 flights. Factors contributing to collisions are discussed, and the two sampling approaches are compared.