Meteorologists use Doppler radar to track precipitation across the country. It provides not only information about falling rain and snow, but also a sense of the direction of the winds, which can help provide information about potential severe weather such as tornadoes. But Doppler radar can also track other things in the sky, such as bats, insects and birds.
AgWeb had an interesting article with accompanying video earlier this week on a novel use for Doppler radar in tracking waterfowl that could be carrying avian flu. This devastating disease has killed millions of birds and is a grave risk for poultry farmers, so any information about the path of avian flu-infected wild birds is going to be very useful to the farmers. You can read the story here.