New research has found that there were once, probably are, and almost certainly will be many more species of hummingbird than are known at present.
Using 284 of the world's generally accepted 338 hummingbird species to produce the largest ever family tree of the Trochilidae, the just-published paper suggests that all eight emerald hummingbird genera should be split further, and that distinctive species like Marvelous Spatule-tail are nested within larger genera, in this case the pufflegs Eriocnemis.
The huge phylogenetic analysis also reveals much of the family's history. The common ancestor of hummingbirds, swifts and treeswifts first split in Eurasia around 42 million years ago, and the ancestral hummingbird had entered North America by 22 million years ago. Reaching the Andes mountains resulted in a huge radiation in the family, giving at least 140 species today, partially driven by adaptations to different altitudes. Another driver of the family's radiation has been its total reliance on flower nectar, causing bill shape to evolve into considerably varied shapes - up to 25 species can co-exist at the same site because of this.
Bee hummingbirds and their close relatives have speciated rapidly – in just five million years, around 35 species have evolved. The rather drab hermit hummingbirds have been traditionally viewed as being in their own subfamily Phaethornithinae, sister to the true hummingbirds Trochilinae, but are in fact closely related to the brightly-coloured topaz hummingbirds. These two groups now form a modest outlier as the most ancestral hummingbirds.
The authors say that the dynamic speciation of the group is still in flux, and that there is the potential for many – perhaps hundreds – more species to evolve in the geological near future. The possibility of the naming and splitting of new extant hummingbirds is also left tantalisingly open by the research.
McGuire, J A, Witt, C C, Remsen Jr, J V, Corl, A, Rabosky, D L, Altshuler, D L, and Dudley, R. 2014. Molecular Phylogenetics and the Diversification of Hummingbirds. Current Biology: doi:10.1016/j.cub.2014.03.016