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
Human uses of birds birds, while John James Audubon's enormous and impressive images of birds in his 1827–1838 "Birds of America" are among the most admired by art critics and by collectors: early editions fetch among the highest prices paid for any printed books. The ornithologist John Gould's bird illustrations, in books such as "A Century of Birds hitherto unfigured from the Himalaya Mountains" (1830–1833) with 80 plates, and his 7-volume "The Birds of Australia" (1840–1848) with 600 plates, related directly to his research, were both beautiful and scientifically useful. Birds are popular characters in children's books, which are often handsomely illustrated. Beatrix Potter's