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
Birds of Cornwall Birds of Cornwall The birds of Cornwall are in general a selection of those found in the whole of the British Isles, though Cornwall's position at the extreme south-west of Great Britain results in many occasional migrants. The nightingale is one common English bird which is virtually absent from Cornwall. The tidal estuaries along the coasts contain large numbers of wading birds, while marshland bird species frequently settle in the bogs and mires inland. Bodmin Moor is a breeding ground for species such as lapwing, snipe and curlew. On and around the rivers, sand martins and kingfishers are often seen.