Wind turbines killing birds and bats - some perspective

That old chestnut, much beloved by a certain Donald Trump, is in the news again, thanks to a British study from the University of Exeter which claims that millions of bats (which is what this particular study focussed on) are possibly being killed each year by wind turbines.

I say "possibly" because the study is a little vague. It used sniffer dogs to hunt for bat carcasses around British wind farms, and then bulked up the results by an unknown factor on the assumption that many carcasses would have been spirited away by predators and scavengers, which does not sound very scientific to me. The study concluded that 194 bats a month were being killed at the 29 windfarms studied. Bulked up for potentially missing dead animals and extrapolated across the rest of the country, they arrived at an alarming figure of 80,000 bats a year that COULD be dying due to wind turbines.

Estimates of bat deaths from wind turbines in North America are in the region of 500,000 a year, particularly migratory tree bats like hoary bats, so this is clearly a significant problem. They can die from collisions with turbine blades or just from approaching too close and dying from barotrauma from the rapid pressure change.

Now, there does seem to be a dearth of research on the effects of windfarms on bats, and there are many unknowns still to be investigated, e.g. do they turn off their echo location when high in the air away from predators? (that sounds very unlikely to me as that is how they hunt insects), would ultrasound warnings at the top of turbines deter them? (that is just my own suggestion off the top of my head, although I have since found out that this is already a thing), changing blade speeds during low wind speed conditions and migration periods, etc. New research in Scandinavia also suggests that a solution as simple as painting one turbine blade black could save many thousands of birds and possibly bats.

But the notion of birds and bats throwing themselves at wind turbines in some kind of mass suicide pact has been studied to death (so to speak), and the common claims are overstated, especially when compared to some other major causes of death.

A good summary of these arguments can be found at TreeHugger.com, an admittedly partisan source, but a bit of perspective when taken together with some of the more alarmist claims out there. Pulling together data from over 100 other studies in the USA and Canada, seems that between 214,000 and 368,000 birds annually are killed by collisions with wind turbines across the whole of North America, which sounds like a lot until you compare it to the 6.8 million birds killed by collisions with cell and radio towers, and between 1.4 billion and 3.7 billion killed each year by cats.
One particularly illuminating image (below), taken from the North American Bird Conservation Inititative's State of North American Birds 2014 report, shows graphically the causes of deaths of birds, starting with cats (far and away the biggest culprit at an estimated 2.4 billion in the USA alone), followed by building windows (599 million), then automobiles (200 million), then power line collisions (25 million), then communication towers (6.6 million), then power line electrocutions (5.6 million), then agricultural chemicals (figures not available), and finally almost as an after-thought, wind turbine collisions (234,000).

The article also points out that hundreds of species of birds are threatened by climate change over the next decades, and those wind turbines are helping to reduce the impact of climate change, and thus actually saving thousands of birds.
Still concerned about windfarms?