If your robins are already back, students can still enjoy the challenge of figuring out whether the 36-degree isotherm applied to your area by going back to records of daily high and low temperatures. OR, you may wish to test the isotherm theory to see whether it applies to the appearance of earthworms in your area. You can also choose another location farther north and watch for correlations between the 36-degree isotherm and the arrival of robins in that geographic area. Let's hear it for the fourth-graders from Ms. Sheer's class, the Fifth graders from Tom Longboat P.S. in Scarborough, Ontario, and seventh graders from Iselin Middle School in New Jersey. Robins flap constantly while flying, unlike hawks and eagles, which soar and rely on thermal air currents or updrafts to hold them aloft.
Thermals can carry hawks and eagles very high in the sky.
Since these birds aren't doing as much work as flapping robins, they can more easily handle the thin atmosphere at high altitudes. Nocturnal migrants can't see where they're going, and navigate by the stars. They need to be above low clouds to see the stars, and need to be high enough up that they won't collide with hills, mountains, and other obstructions that robins flying in the daytime can easily see. The worms very likely rise to the top quicker on fields than they do on lawns because the bare soil is darker than grass, collects more sunlight, and therefore warms up faster. Yes, the robins are probably eating worms or insects in the seeds.