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 in music Birds in music Birds have played a role in Western Classical music since at least the 14th century, when composers such as Jean Vaillant quoted birdsong in some of their compositions. Among the birds whose song is most often used in music are the nightingale and the cuckoo. Composers and musicians have made use of birds in their music in different ways: they can be inspired by birdsong; they can intentionally imitate bird song in a composition; they can incorporate recordings of birds into their works, as Ottorino Respighi first did; or, like the cellist Beatrice Harrison in 1924 and