The tropics have variously been argued to represent a cradle of diversity, a museum of diversity, or some combination of the two. Few broad scale data have been available to examine these mechanisms. For the avifauna of the New World, the tropics appear, at least, to act as a museum. The mean age of tribes is greatest at the equator and declines towards the Poles, whether or not the mean is weighted by the number of species in the tribe. The decline is asymmetrical, being much more severe in the northern hemisphere. The pattern results predominantly from a progressive loss of older tribes towards higher northern latitudes. Some mechanisms that might generate these patterns are discussed.