Here’s an alarming but little-known figure—stray cats and pet cats allowed outdoors kill 3.6 million birds every day on average in the United States, for a total of at least 1.3 billion birds per year. That’s most likely a sizable chunk out of the U.S. land-bird population, which the Smithsonian Migratory Bird Center estimates is around 10-20 billion....[snip] But some cat lovers are also bird lovers. Two of them, a birdwatcher named Nancy Brennan and a bird biologist named Susan Willson, have developed what they believe is a solution...