Most detailed bird evolutionary tree reveals new and surprising relationships (2024)

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The smallest flying birds might be more closely related to the largest than previously thought.

A new genetic analysis of all the families of birds has found that hummingbirds and albatrosses form part of an entirely new group of birds, whilst it has also revealed that as opposed to other studies the eagles and owls are actually each other’s closest relatives.

The researchers have used the genetic information from 363 species of birds covering 92% of all bird families to piece together an immense family tree. This is the most complete, highest-resolution evolutionary tree for birds created to date.

Professor Guojie Zhang is a professor on evolutionary biology at Zhejiang University and senior author of this research. He says, “the amount of data is vastly increased from before, with exceptionally wide taxonomic coverage and detailed genomic sequence information.”

“Eventually we want to obtain sequence data on all living species of birds. The combination of genomic, ecological and behavioural data from thousands of bird species will be essential for combating diseases like avian influenza, and they will be a treasure trove for conserving birds worldwide.”

The research is part of the Bird 10,000 Genomes (B10K) Consortium, which aims to sequence the genomes of every single species of bird. The study was led by Zhang together with Assistant Professor Josefin Stiller from the University of Copenhagen and Associate Professor Siavash Mirarab from the University of California, San Diego, and has been published in the journal Nature.

In the wake of the dinosaurs

Birds are an extraordinarily diverse group of animals. They can be found on every single continent, living in environments ranging from the driest desert to the wettest rainforest.

Within these habitats, they have further diversified to exploit a massive number of different niches. There are birds that dive hundreds of metres beneath the waves for fish, some which crack the hardest of nuts, and those that have evolved in tight association with plants that provide their high-sugar nectar. Others still have specialised in eating other birds, or cleaning up the carcasses left behind by larger mammals.

While the general relationships between birds, and those between species within specific groups, have been fairly well studied and understood, where exactly many groups of birds sit with relation to each other has been surprisingly difficult to figure out.

For example, the curious hoatzin is a species of bird found living along the banks of the Amazon River. It is so evolutionarily distinct, living entirely on a diet of leaves and producing chicks that still retain a claw on their wings, that it forms its own distinct group which scientists have long struggled to place. It is so unusual, the hoatzin doesn’t seem to be obviously related to any other group of birds.

This is because there is a point in time when there was a flash of evolution within birds, a flurry of diversification at about the same time as when the asteroid that wiped out their dinosaur cousins hit. But even then, there has still been a debate as to whether this burst of evolution occurred before or after the dinosaur extinction event.

The much improved precision in dating from this new paper seems to have finally settled this.

Dr Martin Stervander is the Senior Curator of Birds at National Museums Scotland, and a Scientific Associate at the Natural History Museum.

“The cool thing with the dating is that we can actually show that almost all of that diversification happened after the meteorite,” explains Martin, who was involved in this latest paper. “It looks like almost all of the diversification happened when a lot of the competitors for niches and space were wiped out, but our lovely winged friends survived.”

This period of extremely rapid evolution, as the birds moved into new environments and niches left vacant by the dinosaurs, is the reason why it has been hard for biologists to tease out which groups – such as the hoatzin – are most closely related to each other.

But the input of vast amounts of genetic data from right across the range of bird families is finally starting to reveal some of these relationships. One of the biggest changes is the creation of an entirely new group of birds.

Meet the elemental birds

The research has found that a seemingly diverse group of birds actually cluster together in one new group.

This includes many species you might expect to be related, such as pelicans, penguins and albatrosses, but also a whole bunch of other perhaps more unusual species, including the swifts, hummingbirds and those pesky hoatzins. It is the surprisingly diverse lifestyles of these birds – including the smallest and largest flying birds – that gave inspiration to their new name.

“We named this new group Elementaves,” explains Martin. “This is because the birds within this group have diversified into aquatic, terrestrial, and aerial niches – including some of our most impressive specialists like penguins and swifts – corresponding to the classical elements of water, earth, and wind.”

“But what about fire? Well, sunbittern and tropicbirds of Phaetontimorphae have names derived from the sun, which is a big ball of fire.”

The other perhaps logical – but no less surprising – reshuffling from the paper involved the eagles and owls. Despite having similar lifestyles and adaptations, albeit working different shifts, the birds have traditionally these have been placed in separate branches of the family tree. They have now been brought together.

“Another new finding is that diurnal raptors like eagles and buzzards indeed make up the sister lineage to owls, the raptors of the night,” says Martin.

Whilst this latest work has produced the most detailed bird evolutionary tree to date, that’s not to say it won’t change again. The B10K project aims to sequence the genomes of every single species of bird, and there is no saying how this might reveal yet more surprises in the evolution of birds.

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