It is likely that this group originated in northern Central America, where the greatest number of species and diversity between them is found. From there they spread north during the interglacial periods, mainly as migrants, returning to the ancestral region in winter. Two genera, Myioborus and Basileuterus, seem to have colonized South America early, perhaps before the two continents were linked, and together constitute most warbler species of that region.
The scientific name for the family, Parulidae, originates from the fact that Linnaeus in 1758 named the northern parula as a tit, Parus americanus, and, as taxonomy developed, the genus name was modified first to Parulus and then to Parula. The family name derives from the name for the genus.
All the warblers are fairly small. The smallest species is the Lucy's warbler (Oreothlypis luciae), at about 6.5g and 10.6cm (4.2in). Which species is the largest depends upon which are to be included in the family. Traditionally, this was considered to be the yellow-breasted chat, at 18.2cm (7.2in). Since this may not be a parulid, the Parkesia waterthrushes, the ovenbird, the russet-crowned warbler and Semper's warbler, all of which can exceed 15cm (5.9in) and 21g, might be considered the largest.
The migratory species tend to lay larger clutches of eggs, typically up to six, since the hazards of their journeys mean that many individuals will have only one chance to breed. In contrast, the laying of two eggs is typical for many tropical species, since the chicks can be provided with better care, and the adults are likely to have further opportunities for reproduction.
Many migratory species, particularly those which breed further north, have distinctive male plumage at least in the breeding season, since males need to reclaim territory and advertise for mates each year. This tendency is particularly marked in the large genus Setophaga (formerly Dendroica). In contrast, resident tropical species, which pair for life, show little if any sexual dimorphism. There are of course exceptions. The Parkesia waterthrushes and ovenbird are strongly migratory, but have identical male and female plumage, whereas the mainly tropical and sedentary yellowthroats are dimorphic. The Granatellus chats also show sexual dimorphism, but due to recent genetic work have been moved into the family Cardinalidae (New World buntings and cardinals).
There are a number of issues in the taxonomy and systematics of the Parulidae.
The New World warblers are closely related to the tanagers, and some species like the conebillsConirostrum and the bananaquit have been placed into either group by different authorities. Currently, the conebills are normally placed in Thraupidae and the bananaquit in its own family.