Avian clutch size of increasing clutch size with increasing latitude. The proximate and ultimate causes for this pattern have been a subject of intense debate involving the ideas of group and individual selection. David Lack observed a direct relationship between latitude and avian clutch size. Birds near the equator laid approximately half as many eggs as those that resided in northern temperate habitats. He observed an increasing clutch-size from the equator towards the poles (something he referred to as the “latitude trend”) for many passerine (perching) birds, near-passerine (tree-dwelling) birds and in various other groups: Strigiformes, Falconiformes, Ciconiiformes, Laridae, Ralliformes, Galliformes, Podicipedifomes, and
Extinct Birds Extinct Birds Extinct Birds (complete title: Extinct birds. An attempt to unite in one volume a short account of those Birds which have become extinct in historical times—that is, within the last six or seven hundred years. To which are added a few which still exist, but are on the verge of extinction.) is a book by Walter Rothschild which covers globally extinct and rare birds as well as hypothetical extinct species which include bird taxa whose existence is only based on written or oral reports or on paintings. The accounts of the extinct bird taxa are based on Rothschild's