It has been observed that folivory is extremely rare among flying animals. Morton (1978) attributed this to the fact that leaves are heavy, slow to digest, and contain little energy relative to other foods. The Hoatzin is an example of a flighted, folivorous bird.
Arboreal folivores, such as sloths and some species of monkeys and lemurs, tend to be large and climb cautiously. Similarities in body shape and head- and tooth-structure between early hominoids and various families of arboreal folivores have been advanced as evidence that early homonoids were also folivorous.
Folivorous primates are relatively rare in the New World, the primary exception being howler monkeys. One explanation that has been offered is that fruiting and leafing occur simultaneously among New World plants. However a 2001 study found no evidence for simultaneous fruiting and leafing at most sites, apparently disproving this hypothesis.
Effects of synchronization with host plant phenology occur early in the larval development of a spring folivore.
Apr 01, 2006; Abstract: Early spring feeding Lepidoptera depend on synchronization of larval emergence with host plant phenology for optimal...