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
Gleaning (birds) These features are even seen in gleaning birds that are not closely related. For example, in flycatchers of the family Tyrannidae, in which some member species are more adapted for hawking insects on the wing and others for gleaning, the gleaners have bills that resemble those of tits and warblers, unlike their larger-billed relatives. Also, some members of the woodpecker family, particularly piculets such as the rufous piculet of Southeast Asia, are similarly adapted for gleaning, with small, compact bodies and sharp bills, rather than the long, supportive tails and wedge-shaped bills more typical of woodpeckers. Birds such as the