Bird and bat behavior and mortality at a northern Iowa windfarm

• Main Author: Jain, Aaftab Ashok
• Format: Text
• Language: English
• Published: Iowa State University Digital Repository 2005
• Subjects: Natural resource ecology and management; Ecology and evolutionary biology; Canada; Branta canadensis; Canada Goose
• Online Access: https://lib.dr.iastate.edu/rtd/19562; https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=20561&context=rtd

We examined bird and bat collision mortality and activity at an 89-tower wind resource area (WRA) in north-central Iowa, from April 15, 2003 to December 15, 2003 and March 15, 2004 to December 15, 2004. We also examined Canada goose (Branta canadensis) foraging and vigilance in the fall of both years. We found 2 birds and 30 bats in 2003 and 5 birds and 45 bats in 2004, in search transects and gravel access areas under towers. We applied search correction factors and estimated total bird mortality at 39.47 [plus or minus] 4.60 (95% CI) in 2003 and 85.38 [plus or minus] 7.78 (95% CI) in 2004. We estimated total bat mortality at 587.78 [plus or minus] 28.95 (95% CI) in 2003 and 785.87 [plus or minus] 40.00 (95% CI) in 2004. We found a considerable proportion of non-migratory little brown bats (Myotis lucifugus). Bird abundance did not differ significantly between tower and non-tower sites. Bird flight close to the tower at rotor height was rare. Across species birds tended to avoid the 0-30m zone closest to towers. These behaviors possibly reduce the risk of collision mortality. We found no significant difference between ultrasonic bat calls detected at tower ([− over x] - 34.88 calls/detector-night) and ([− over x] = 36.57 calls/detector-night) non-tower sites. Most calls were of little brown bats. The fall migratory period had the highest bat activity and collision mortality. The WRA has wetland management areas in close proximity and overlaps an area closed to Canada goose hunting. We created a model to estimate the effect of the presence of a wind tower in a field on the use of that field by goose flocks. In 2003 and 2004, our models found no evidence that the towers affected goose field choices. We also estimated whether vigilance behavior differed between flocks foraging in WRA fields and non-WRA fields within the area closed to Canada Goose hunting, and found no significant difference (F = 0.01, df = 1, 59, P = 0.92). The WRA had minimal impact on birds in the region, but more research is needed on the behavior of bats while engaged in collision-prone flight at rotor heights.