http://www1.eere.energy.gov/windandhydro/pdfs/birds_and_bats_fact_sheet.pdf…
Early turbines were mounted on towers 60–80 feet in height and had rotors 50–60 feet in diameter that turned 60–80 revolutions per minute (rpm). Today's land-based wind turbines are mounted on towers 200–260 feet in height with rotors 150–260 feet in diameter, resulting in blade tips that can reach over 425 feet above ground level. Rotor swept areas now exceed 1 acre and are expected to reach nearly 1.5 acres within the next several years. Even though the speed of rotor revolution has significantly decreased to 11–28 rpm, blade tip speeds have remained about the same; under normal operating conditions, blade tip speeds range from 138–182 mph. Wider and longer blades produce greater vortices and turbulence in their wake as they rotate, posing a potential problem for bats. Because large turbines are more efficient, most modern wind developments for a given number of megawatts (MW; 1 MW equals 1 million watts) have fewer machines with wider spacing. Still, larger turbines are being developed.
…
Studies have indicated that relatively low raptor (e.g., hawks, eagles) fatality rates exist at most wind energy developments with the exception of some facilities in parts of California (Figure 1, page 3). All developments studied have reported fewer than 14 bird (all species combined) fatalities per nameplate MW per year, and most have reported less than 4 fatalities per MW per year (Figure 2, page 3). Although several developments have reported relatively numerous bat fatalities, most studies have reported low rates of such bat fatalities (Figure 3, page 3). However, much uncertainty exists on the geographic distribution and causes of bat fatalities (see discussion under direct mortality).
Two general types of local impacts to birds have been demonstrated at existing wind facilities: (1) direct mortality from collisions and (2) indirect impacts from avoidance of an area, habitat disruption, reduced nesting/breeding density, habitat abandonment, loss of refugia, habitat unsuitability, and behavioral effects (Stewart et al. 2004, 2007). For bats, only direct mortality resulting from collisions and barotrauma (i.e., experiencing rapid pressure changes that cause severe internal organ damage; Baerwald et al. 2008) has been demonstrated.
…
The estimated cumulative impact of collisions with wind turbines is several orders of magnitude lower than the estimated impacts from the leading anthropogenic causes of songbird mortality.
Although only general estimates are available, the number of birds killed in wind developments is substantially lower relative to estimated annual bird casualty rates from a variety of other anthropogenic factors including vehicles, buildings and windows, power transmission lines, communication towers, toxic chemicals including pesticides, and feral and domestic cats (Erickson et al. 2001; NAS 2007; Manville 2009). Collisions with wind facility structures will likely increase relative to other anthropogenic structures as the number of wind power facilities increases.
…
Printer-friendly format
Email this thread to a friend
Bookmark this thread
(1000+ posts)
Send PM |
Profile |
Ignore
