13 April 1984
Vol 224, Issue 4645

About The Cover

Individuals from three populations of Hemispingus superciliaris, a small tanager of the Andes that illustrates the “leapfrog” pattern of geographic variation. Yellow populations of the northern and southern Andes are geographically separated by very differently colored gray populations in central Peru. This type of pattern is found in about 20 percent of all Andean birds with three or more subspecies. See page 171. [Painting by John P. O'Neill, Museum of Natural Science, Louisiana State University, Baton Rouge 70803]