There are many things in the world that we cannot see with our eyes, including the hundreds of millions of birds that migrate in the spring and fall under cover of darkness. I wrote about radar ornithology, a field of study that uses weather surveillance radar to track birds at night, and a group of scientists who are using artificial intelligence to try and interpret the data and glean the relationships between ecology, climate and migration for the goal of conservation. The piece is here at Nautilus magazine's issue on "Dark Matter."