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Bird populations worldwide are increasingly threatened by anthropogenic alteration of their habitats. Collisions with power lines, poles, and wind energy structures can be a major
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source of bird mortality. Ventana Wildlife Society, working cooperatively with our funding partners, is committed to providing quality research that evaluates local risks and potential solutions for improving avian conservation and ensuring compliance with federal regulations. We are pleased to begin a study for the City of Soledad assessing avian and bat use of two proposed wind energy sites in the Salinas Valley. Recently completed projects include drafting an avian protection plan for the Camp Roberts Army National Guard training site and evaluating the effectiveness of flight diverters in reducing avian collisions with distribution lines at San Luis National Wildlife Refuge. A synopsis of the diverter study follows
Project: Evaluating diverter effectiveness in reducing avian collisions with distribution lines at San Luis National Wildlife Refuge Complex, Merced County, California, USA
Project Funded By: California Energy Commission, Pacific Gas & Electric Company, and Edison Electric Institute
We conducted flight observations and carcass searches at six sites at San Luis National Wildlife Refuge Complex, Merced County, California to evaluate the effectiveness of Bird-Flight Diverters (BFD) and Swan-Flight Diverters (SFD) at reducing avian collisions with power lines, and identify conditions associated with collisions.
In 791 hours of observation in three winter seasons from 2005 to 2008, we observed few actual collisions; but we documented many reactions to power lines, such as altitude changes (n=1,863) or more sudden changes in flight direction, called flutter/flares (n=316). Birds exhibited reactions at greater distances from power lines after diverters were installed, especially on SFD lines. Along with the presence or absence of diverters, wind conditions and site were the strongest predictors of a flutter/flare reaction.
Based on 403 carcass recoveries, adjusted to account for searcher and scavenger bias, 550 total collisions were estimated in two winter seasons from 2006 to 2008. Estimated total collisions were significantly higher for control lines than for BFD or SFD lines. The difference between control and diverter lines was even greater when the analysis excluded American Coot, a species accounting for approximately half of all carcasses found. Although conclusions regarding diverter effects are limited by the lack of carcass searches before diverter installation, the consistent pattern of more estimated collisions at control lines, along with the increase in reaction distances after diverters were installed, indicate that both diverter types had a positive effect on reducing the number of avian collisions at San Luis National Wildlife Refuge Complex.
Both diverter types, however, were apparently ineffective for American Coot, which flies at night. To improve protection for coots and other species with nocturnal flight habits, diverters that illuminate at night or in low-light conditions should be added at high-risk sites. Because a variety of factors, such as weather and location, can influence the risk of avian collisions, even with diverters on the line, managers should continue to monitor avian mortality after diverter installation and respond to local conditions warranting additional protection.