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
Hawking (birds) tight spaces. Birds in more open settings that sally after larger insects like bees, such as kingbirds and bee-eaters, benefit from longer, more pointed wings, which are more efficient because they generate more lift and less drag. Swallows and swifts, which glide about in totally open spaces, have even longer wings. Another function of long, pointed wings is to enable these birds to turn quickly and smoothly in mid-glide. The wingtips create little vortices of air, within which the low air pressure creates additional lift on the wingtips. Furthermore, long, forked tails provide additional lift, stability, and steering ability, which