Before migrating to Paonia, I spent time in the backwoods of southwestern Oregon, occasionally on the porch of a cabin with a colony of bats living under its shingles. Each afternoon, the walls began to creak and moan like old floorboards. Then the bats — hundreds of furry clamshell bodies — would slip out, unfurl, and fly off for their nightly dose of mosquitoes. They arrived in July, and left in November for warmer climes. This morning, as I walked to the HCN office in sub-20-degree weather, they probably were falling asleep in the dark thatching of a Mexican cabana.
They’ll be back in Oregon next summer, hopefully. But bats, like birds, face risks as they travel — one of which is the increasing number of wind turbines in the West (see our short article “Blades, birds, and bats”).
Bat migration is less common than bird migration, and little understood. Now, however, a study in the Journal of Mammalogy suggests that tree-roosting species, like the hoary bat and the silver-haired bat, fly along predictable routes with easy, leafy “stopovers”— even if that means they fly farther overall — and that locating wind farms accordingly will save their lives. These bats are especially likely to encounter mammoth blades along forested foothills. In grasslands, though, limbs and trunks are scarce, as are the landmarks bats use to navigate north and south. For bats at least, it would be best if future rotors sprouted in wide-open spaces.
The study also points out that, depending on the species, bats traveling the same corridor cruise at different altitudes. The silver-haired bat wings low to the ground, for example, while the hoary bat jounces along one hundred feet in the air, a difference attributed to their body types and hunting styles. So both location and tower size should be considered when siting new turbines. Those wind farms with tons of bat activity and tall towers typically cause the most fatalities, but perhaps that won’t hold true in all cases.
Of course, planting wind farms elsewhere, or adjusting their height, might negatively affect other creatures, like sage grouse. What’s needed are more impact studies that include bats, birds, and all beasts, including humans.
If you’re feeling especially batty today, also check out Emily Underwood’s excellent, albeit alarming, blog post from May 2009: “Fatal attraction?”
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