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
Dawn chorus (birds) bellbird and the tui are two of the birds that would have formed part of the dawn chorus since they have a vocal and melodious call. In the UK the dawn chorus may begin as early as 3am in early summer. The most often heard species of birds are, in order of them beginning to sing: Several primate species vocalise early in the morning as an audible territorial display. These include the lesula ("Cercopithecus lomamiensis"), the black howler ("Alouatta caraya") (which can be heard 5 km away) and the mantled guereza ("Colobus guereza"). Dawn chorus (birds) The dawn chorus occurs