Warblers

Warblers are small, perching song birds with a large number of species distributed throughout the world. There are two families of warblers, one in the New World and one in the Old World. The New World warblers (family Parulidae) comprise 113 species that occur throughout the Americas. The Old World warblers (family Silviidae) occur in Eurasia, Africa, and Australia, and include some 325 species. Although the warblers in these two families are not closely related, having evolved from different ancestral stocks, they are of rather similar general appearance, and many species in both families are accomplished singers. These are the main reasons for their shared common name.

In addition, birds in both families of warblers are very active hunters of insects, spiders, and other small invertebrates. Most species of warblers are tropical or subtropical. However, many migratory species of warblers breed in forested and shrubby habitats at higher latitudes, and spend the non-breeding season in warmer latitudes. These migratory warblers can be regarded as essentially tropical birds that breed and raise their young in the forests of higher latitudes in order to take advantage of the seasonal abundance of arthropods.

The Old World and American warblers bear a superficial resemblance to each other. This is largely because of convergent evolutionary influences, resulting from the fact that these unrelated birds occupy rather similar niches in their ecosystems—that of small, arthropod-eating birds. One difference between the families is the occurrence of 10 primary wing feathers in the Silviidae, compared with nine in the Parulidae. The American warblers, particularly male birds, tend to be much more brightly colored than the Old World warblers.