Christopher Pratt

Clouds are formed when currents of warm air called THERMALS rise from the ground and begin to cool. Thermals themselves aren’t visible until this point, unless there are birds interpreting their movements and riding on them. Birds are said to “catch” a thermal the way we might catch a bus—by floating up to high altitudes and gliding back down, over and over again, across great distances with very little effort. Birds that can be seen doing this include the common Turkey Vulture, identifiable from below by its enormous silhouette and the V-shaped shadow of its shoulders seen through its wings against the overhead sunlight.