A recent genetic study proposes six subfamilies.
Ornithologists are often arguing about the species status of particular birds: are they distinct species or just subspecies?! The discussions about other taxonomic levels, such as genera or subfamilies, are often less heated. There is no clear consensus among taxonomists on how to determine whether a group of species should be classified in the same genus or subfamily. However, these higher-level classifications can be important to understand the evolutionary history of a particular lineage and should thus reflect some underlying characteristics in terms of genetic divergence or morphology. A recent study in the journal Molecular Phylogenetics and Evolution applied this reasoning to the bird family Estrildidae: the estrildid finches.
The taxonomic limits within the Estrildidae are still controversial. Several studies have resolved certain sections within this family, but no complete species-level phylogeny has been published yet. The most comprehensive classification of the estrildid finches can be found in the Handbook of Birds of the World, but is based on unpublished data. Currently, the Estrildidae family is divided into three subfamilies: Estrildinae (mainly African waxbills), Lonchurinae (grassfinches, mannikins and munias), and Erythrurinae (parrotfinches).
That is why Urban Olsson and Per Alström decided to sample as many species as possible and reconstruct their evolutionary history. Genetic analyses uncovered six distinct groups within this family. The authors propose to consider these six groups as subfamilies, because “the relatively similar age of the six clades is a strong argument for treating them at the same taxonomic level.” Indeed, the molecular dating analyses revealed that these groups originated about 10 million years ago. The names for these subfamilies would be Amandavinae, Erythrurinae, Estrildinae, Lagonostictinae, Lonchurinae and Poephilinae.
One or Two Genera?
There are some interesting patterns within the newly recognized subfamilies. Take the genus Coccopygia, for example. This small group of waxbills is sometimes classified within the genus Estrilda. This study, however, shows that both genera are actually very different on a genetic level. Moreover, grouping them together would render the genus Estrilda polyphyletic (while taxonomists aim for monophyletic groups). So, better to keep them separate.
Morphology vs. Genes
In the subfamily Lagonostictinae, we find four Pytilia species. These have traditionally been divided into two morphologically similar pairs: red-billed pytilia (P. lineata) with red-winged pytilia (P. phoenicoptera) and orange-winged pytilia (P. afra) with red-faced pytilia (P. hypogrammica). Surprisingly , this arrangement is not reflected in the genetic data. It turns out that the morphologically different red-winged pytilia and red-faced pytilia are closely related. Possibly, there has been (or still is) gene flow among these two species that live side by side in western Africa.
There might thus be hybrids between Pytilia species to be discovered. A genus where hybridization is definitely quite common is Lonchura. A recent genomic study reported high levels of gene flow between certain species, indicating that “they represented a very recent radiation that had not yet developed reproductive isolating barriers.” This conclusion was corroborated by the current study that reported very short branch lengths for these species in the phylogeny.
We might have resolved the main relationships within the Estrildidae family, but there remains much to be unraveled on a lower taxonomic level.
Olsson, U., & Alström, P. (2020). A comprehensive phylogeny and taxonomic evaluation of the waxbills (Aves: Estrildidae). Molecular Phylogenetics and Evolution, 146, 106757.