The Download: AI tracking birds, and a pig kidney transplant

In a warming world, migratory birds face many existential threats. Scientists rely on a combination of methods to track the timing and location of their migrations, but each has shortcomings. And there's another problem: Most birds migrate at night, when it's more difficult to identify them visually and while most birders are in bed. For over a century, acoustic monitoring has hovered tantalizingly out of reach as a method that would solve ornithologists' woes. Now, finally, machine-learning tools are unlocking a treasure trove of acoustic data for ecologists.