The best estimate is that 100 million to a billion birds in North America die this way each year.
Many people - citizen scientists as well as researchers - are doing what they to learn what can be done. The American Bird Conservancy and Powdermill Avian Research Center in Pennsylvania are conducting research. If you live in Minnesota, you can volunteer to assist
Project BirdSafe, a joint effort by Audubon Minnesota, the DNR Nongame Wildlife Program, the Bell Museum of Natural History, the Wildlife Rehabilitation Center, the National Parks Service, St. Paul Audubon Society, the Audubon Chapter of Minneapolis, Zumbro Valley Audubon, BOMA Minneapolis and BOMA St. Paul.