Factors in the design of an urban microbat flyway

Bat surveys were conducted during 2006 and 2007 in the Willoughby Local Government Area (LGA) in the northern suburbs of Sydney to determine the occurrence and movement of microbats. Based on the frequency of bat detections and the direction of bat movements, two major and five minor bat flyways were identified in the study area. The two major flyways were north-south movement corridors that occurred on the eastern and western margins of the LGA; each major flyway had minor flyways branching from them. The two major flyways were separated from each other by the Pacific Highway rise that runs north-south through the centre of the study area. The rise acts as an effective flyway barrier as tree corridors are completely disrupted by an exposed, noisy, night-illuminated residential and commercial strip. Minor bat flyways approach the Pacific Highway rise from the east and west and are only separated by a relatively short distance. Extending these flyways to create an east-west passage across the study area would greatly extend the foraging range of bats on either side of it. In order to link the major flyways, the eastern and western minor flyways need to be extended by the creation of a continuous tree canopy through residential areas to the Pacific Highway rise. Controlled street planting and supported private plantings of trees along strategic routes, together with modified street lighting could achieve this result. The crossing of the Pacific Highway would require the construction of a lightweight “flyover bridge” that commenced and ended in the extended tree canopies. This would provide a wind and light shielded crossing point for bats attempting to fly east-west across the Willoughby LGA. The components of the “flyover bridge” are discussed along with other considerations in achieving an effective extended flyway through a densely populated residential area.