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 available, photographs of the species, its habitat, and of the nest and eggs. Also provided, when available, are recordings of the species' song and calls, selected from the collection in the Macaulay Library at the Cornell Lab of Ornithology and from other online sources, such as xeno-canto. 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