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
Prinia Prinia The prinias are a genus of small insectivorous birds belonging to the passerine bird family Cisticolidae. They were at one time classed in the Old World warbler family, Sylviidae. The prinias are sometimes referred to as wren-warblers. They are a little-known group of the tropical and subtropical Old World, the roughly thirty species being divided fairly equally between Africa and Asia. These are birds mainly of open habitats such as long grass or scrub, in which they are not easily seen. They are mainly resident, migration being limited to local cold weather movements. Non-breeding birds may form small flocks.