Leapfrog: Who Sings?
"I heard a robin singing this morning around 9:00 A.M," reported a South Dakota observer on March 12. "Then I saw a flock of robins this afternoon around 6:30 P.M." How can we tell which robins are here to stay?
Robins usually start singing the very day they arrive in an area. That's because usually the first robins to arrive in an area are the ones that are going to stay and claim territories. Robins coming after these singing robins "jump over" them to migrate farther north. This is what scientists call leapfrog migration. Birds going farther north simply wait it out until weather conditions seem right to continue. So at each latitude, the first birds to arrive are the ones that will stay, and later arrivals jump over them. You can tell the robins who are staying from the robins who are "jumping over" by whether or not they are singing the territorial song.
Photo: Laura Erickson