From the paper's abstract: "The treatment had the largest effect on reduction of raptor fatalities; no white-tailed eagle carcasses were recorded after painting. Applying contrast painting to the rotor blades significantly reduced the collision risk for a range of birds."
A cursory Internet search reveals that raptors (and bats) are particularly vulnerable to wind turbines[0], and many raptor populations have been threatened for a long time due to a variety of threats and biology (they take longer to reproduce and recover).
And if one were to describe all the threats to birds listed here, they are basically iterations under the "loss of habitat" super-category.
Yes, power lines are also a big threat to raptor and other threatened avian populations, but wind turbines (and the power lines they use) are still being built, so reducing avian deaths from both sources seems worth researching and implementing. Especially when the parent article notes how little it would cost to paint the blades during manufacture (vs. post-installation).
> Even if there were twenty times more wind turbines, enough to supply the US with electricity, the number of birds killed, assuming no improvement in wind turbine design, would be about 10 million--still far less than most other causes of bird deaths.
[1] https://www.sierraclub.org/michigan/wind-turbines-and-birds-...