We tested the hypothesis that area represents the primary explanation for t
he latitudinal diversity gradient using breeding terrestrial birds of North
America, the northern Palearctic, Australia and the Afrotropics as our foc
al group. We tested two propositions inherent to the area hypothesis: (1) t
ropical biomes are larger than extra-tropical biomes, and (2) there is a si
gnificant species-area relationship for birds at the biome scale of resolut
ion. Using a more realistic definition of biomes which incorporates the eff
ects of both energy and water, we find no support for either proposition, l
eading us to conclude that the area per se does not explain terrestrial lat
itudinal diversity gradients.