Is a bird more worth saving from extinction if it is evolutionarily unique, as well as physically rare? That’s one challenging question raised by newly published research that factors together the distinct evolutionary history of the world’s bird species, with how healthy their population numbers and prospects for survival are in the present.
Arne Mooers, a professor of biodiversity at Canada’s Simon Fraser University, and colleagues worked for seven years to assess how much evolutionary history a specific bird represents compared to other bird species currently alive. In order to do it, the team developed an evolutionary tree containing all 9,993 known bird species, says Mooers, and then calculated the total amount of time evolutionary processes “worked” to create those species: about 77 billion years. They then ranked the birds by how much of that work each accounted for. The species that top the list go back furthest in evolutionary history, and share that history with few or no living relatives.
The team calculated the total amount of time evolutionary processes “worked” to create those species: about 77 billion years.
The title of “most evolutionarily distinct” goes to the oilbird, a Central and South American species that alone accounts for 80 million years of avian evolutionary history, Mooers says. Its name derives from the layers of fat on oilbird chicks, which have historically been rendered for use as torches.
The average grackle or chickadee, by comparison, has so many close relations that they all “share” the same evolutionary effort.
The research also sets evolutionary distinctness against the International Union for Conservation of Nature (IUCN) Red List, ranking the 575 bird species considered threatened or endangered on that list by their unique evolutionary histories. The Giant Ibis tops the list by this reckoning, followed by the Kagu, the New Caledonian Owlet-nightjar, the Plains-wanderer, and the California Condor.
This information could help conservationists, natural resource managers, and policy-makers set priorities, says Mooers, when trying to figure out how to allocate resources to saving endangered bird species.
The team has also created a compound metric that sets a bird’s evolutionary uniqueness against how widely it can be found in the world. “Some species may be distinct, but they may be spread over a very large range, like the osprey, which has the widest range of any bird in the world,” says Mooers. “Or you could have something like a kiwi or a kakapo, which only lives in one place. You can think of that distinctness being concentrated in a very small place, for that species.”
The project took seven years to complete in part because when it started, there was no single overarching analysis, or evolutionary tree, of bird evolution. “It seems like we have a single perfect tree here,” says Mooers about the final result. “But there is no single perfect tree of birds. So we had to do this over, we had to create many millions of possible trees, and then take the average across those trees to get these metrics. Because there’s still a lot of uncertainty as to who’s related to who. We didn’t even have genetic data for every species.”
The project was risky enough by scientific standards, says Mooers, that the principal researchers opted to limit the potential for career damage. “We didn’t want to have any graduate students doing their PhDs on it, because we didn’t know if we could do it when we started. Nobody had attempted something this big, nobody had built a tree this big before. So we actually actively did not put any students on it.”
Mooers and team did the work in part to support the EDGE: Evolutionarily Distinct and Globally Endangered project. The project has already put the research to work with its list of “Top 100 EDGE Birds” that are at risk of extinction.
“There is a growing realization,” says Mooers, “that science has to start to become useful in the short term rather than the long term in this particular area because of the acute problems.”
Click here for a gallery of some of the world’s most evolutionarily unique birds, including some of the most endangered.
New Caledonian Owlet-nightjar