Question

making towers bird-friendly
the lights on tall communication towers warn pilots to avoid the towers when flying at night. unfortunately, the steady red lights often used on towers have the opposite effect on birds: the bright beams attract and confuse them. instead of avoiding the lights, the birds fly directly toward them, crashing into the towers or becoming entangled in power lines. millions of birds have died this way. however, there is a solution. unlike steady lights, flashing or blinking lights dont attract birds. in response to demands from conservation groups, the federal aviation administration in 2016 began requiring communication towers in the u.s. to use blinking lights instead of steady ones.
what is the main, or central, idea of the passage?
to save birds, communication towers have begun using blinking lights.
birds are attracted to the steady red lights on communication towers.

Explanation:

The passage first explains that steady red lights on communication towers harm birds (attract and confuse them, leading to deaths). Then it introduces that blinking lights don't attract birds and that the FAA now requires towers to use blinking lights to address this issue. The first option captures the overall solution (using blinking lights to save birds) while the second is just a detail about the problem.

Answer:

To save birds, communication towers have begun using blinking lights.