Golden Gate Audubon Society just put up an information page about how many birds are killed in collisions. The uncertainties are pretty high, but even the low-end estimates are huge: at least 100 million birds per year killed in collisions with windows, for example. A lot of these happen one collision at a time — a bird gets hit by a car, or runs into a window that it doesn’t realize is there. But sometimes there are horrific mass-kill incidents, when huge flocks of birds get confused by radio tower lights and fly in circles around them, with birds running into the guy wires at every circuit and falling to the ground with wings broken. There are known things that can be done to reduce all of these causes of mortality, if we can get people to care.