Behavioral Accommodation of Nesting Hawks to Wind Turbines

• Published in: The Journal of wildlife management Vol. 82; no. 8; pp. 1784 - 1793
• Main Authors: WATSON, JAMES W., KEREN, ILAI N., DAVIES, ROBERT W.
• Format: Journal Article
• Language: English
• Published: Bethesda Wiley 01-11-2018; Blackwell Publishing Ltd
• Subjects: Avoidance; Avoidance behavior; Birds; Buteo jamaicensis; Buteo regalis; Buteo swainsoni; collision fatality; Collision mortality; Foraging behavior; Hunting; Nesting; Nesting behavior; Nests; Risk; Rotor blades; Rotor blades (turbomachinery); Rotor speed; Rotors; Satellite tracking; Shutdowns; Telemetry; Territory; Turbines; Wildlife; Wind effects; Wind power; wind power development; wind turbine; Wind turbines
• ISSN: 0022-541X; 1937-2817
• DOI: 10.1002/jwmg.21532

The most direct effects of wind energy development on birds are rotor blade strikes and collisions with wind turbines. Probability of a blade strike is affected by the rates at which a bird visits the rotor swept zone (RSZ), and mitigated by the behaviors it uses to avoid being struck. Between 2011 and 2013, we studied the occurrence and nature of avoidance responses of 3 nesting ferruginous hawks (Buteo regalis), 5 Swainson’s hawks (B. swainsoni), and 2 red-tailed hawks (B. jamaicensis) to turbines built within their territories. Two of 10 breeding males we tracked with satellite telemetry were turbine-collision fatalities, one during the study and the other in the following year. Collectively, nesting hawks displayed no macro-avoidance of turbine projects and flew adjacent to or within RSZs at high rates (x̄ = 0.8 visits/hr, 1.3 min/visit; n = 387 visits during 434 hr of observation) synchronized with morning and afternoon peaks in foraging activity. Passes through rotors accounted for 9.8% of responses. The turbine that hawks approached most closely from collective encounters on each territory accounted for an average of 29% of all visits to RSZs and visitation was greater than expected at turbines <0.8 km from nests (P < 0.001). As rotor speed increased, the frequency that hawks in RSZs flew between turbine rows increased relative to other avoidance behaviors and hawks that were potentially distracted (i.e., hunting or aggressive chasing) increased avoidance flights over and between turbines. The ability of hawks to employ evasive behaviors mitigated blade collision but allowed for close, hourly interaction with turbines that increased risk of collision. Where nesting populations of hawks are at risk, particularly ferruginous hawks, pre-construction siting of wind turbines needs to account for nest locations and expected high rates of hawk visitation to turbines <800 m from nests. On existing projects collision risk can be reduced through operational shutdown of turbines in this zone during 2 daily peaks in hawk foraging in the vicinity where hawks nest, but a greater effectiveness can be achieved by shutdown of specific turbines associated with highest regular use.