(WB) As Dr. Miller mentioned, we're trying to recruit volunteers for the Hawk Mountain Sanctuary. But before I get into the details of the volunteer program, I'd just like to tell you a little about what we do there.
One of our main jobs is to keep detailed records of the migration patterns of raptors. For those of you who don't know, raptors are birds of prey, like hawks and eagles. Between August and December, we see around twenty different species migrating from Canada and New England --- about 20,000 birds.
Part of what attracts them to Hawk Mountain is the location on the east ridge of the Appalachian Mountains. What happens is that the sun warms the ridge in such a way that air currents are formed. The birds just sort of glide along on the air --- so they use up very little energy.
As volunteers you'll be helping us keep accurate counts of the raptors. Any drop in number could mean something's gone wrong in the environment --- because of pesticides or disease --- even hunting.
We just had a scare with the broad-winged hawks. Their numbers have dropped drastically over the last ten years. It was suggested that the birds may have changed their migratory route. So for 11days we had several hundred volunteers --- stationed every five miles --- to observe and count. And sure enough, they discovered that instead of hugging the Appalachians as they'd always done, the broad-wings were cutting a wide path over the Delaware River. Needless to say, we were greatly relieved.内容来自 听力课堂网：http://www.tingclass.net/show-8562-246818-1.html