When a bird hits the glass, what to measure?

The Minnesota Sports Facilities Authority is expected to announce later this month a study on whether the glass on the new Vikings stadium is harmful to birds.

Conservationists have raised concerns that a great number of birds will be killed when they try to fly through the stadium's glass walls. Stadium officials so far have been unwilling to add a coating to make the glass more visible to birds.

Christine Sheppard, a bird collisions campaign manager for the American Bird Conservancy, discusses how a study could be set up.