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
Neotropical Birds Online Neotropical Birds Online Neotropical Birds Online is an online encyclopedia whose subject is the bird species that breed in the Neotropics. "Neotropical Birds Online" is patterned after "Birds of North America". Each account profiles a single species, and the accounts are published in the order in which they are completed. The project is sponsored by the Cornell Lab of Ornithology at Cornell University, a leading US research center in ornithology. The list of species covered by "Neotropical Birds Online" is based on the two avian checklist committees of the American Ornithologists' Union: the North American Classification Committee (NACC), which is