There May Be Twice As Many Species Of Birds Than Is Currently Recognized

purple crested turaco

Could there actually be two species of purple crested turacos? JMx Images/Shutterstock

It seems that there may actually be twice the number of birds soaring the skies, plunging the depths, and burrowing in the earth than scientists currently think. A new study has found that we may be drastically under-representing our avian brethren. 

It is fairly well established that there are roughly 9,000 species of birds, ranging from the mighty ostrich to the teeny, tiny bee hummingbird. Having been intimately studied by scientists and researchers for hundreds of years, it is genuinely thought that this is an accurate figure for how many there are. Yet this number tends to be based on the traditional “biological species concept”, in that if two birds can breed, then they are therefore the same species.


Not so, say the authors of the new study published in PLOS One.

“It's really an outdated point of view, and it's a concept that is hardly used in taxonomy outside of birds,” said lead author George Barrowclough, from the American Museum of Natural History’s Department of Ornithology. Since this definition was first proposed, the more scientists have looked, and the more exceptions to the rule have been found. For example, blue whales and fin whales have been found to hybridize, with the offspring produced then going on to reproduce themselves.

To address this, the researchers have taken a random sample of 200 species of birds and looked not at whether they can breed together or not, but at their morphology instead. By looking at these physical characteristics, from their plumage to their bill length, they found that on average there were in reality nearly two individual species for every one studied. This meant that they were really looking at closer to 400 different species.

When extrapolated for all the known 9,000 species of birds, it could mean that there are really closer to 18,000. This was then compared to recent genetic evidence that suggests that the number could be anything as high as 20,000 species, though the authors admit that those studies were probably overestimating somewhat. “Our study provides a glimpse of what a future taxonomy should encompass,” said Joel Cracraft, who co-authored the paper.


The research reignites an age-old debate between the “splitters” and the “lumpers.” One side of the argument maintains that there are many more animals than we recognize and so prefer to “split” species, while the other says that there are far fewer and so “lump” species together.

While this debate is unlikely to be settled anytime soon, it is hoped that this latest study may help direct conservation and management practices to better focus on those places and species most in need, and help to direct future research.


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  • evolution,

  • genetics,

  • birds,

  • species,

  • avian,

  • morphology