In the midst of today's global extinction crisis, decisions about conservation should include prioritizing how best to preserve as much of the tree of life as possible. So say researchers who report in the Cell Press journal Current Biology on the first application of an approach to identify the most evolutionarily distinct of the world's 9,993 bird species.

At the very top of their list of the most evolutionary distinct birds is the South American oilbird, which represents almost 80 million years of evolution shared with no other bird on the planet.

"Evolutionary distinctness is a metric that informs about the loss of evolutionary information that the extinction of a given species would cause," says Walter Jetz of Yale University. "Among very closely related species, we would expect a lot of genetic redundancy. If there is only one of a kind, say an oilbird, and it were to go extinct, all of the information on how to make and be that species would be lost forever. Thanks to global family trees, we are able to now compare this aspect of distinctness for all species, something that due to lack of data is not possible for any other characteristics."

"Evolutionary distinctness helps us identify those species we cannot afford to lose," says coauthor Dave Redding of University College London.

In the new report, the researchers performed the first fully quantitative, phylogenetically and geographically integrated conservation assessment for birds all around the world. Evolutionary distinctness was quantified for each species based on how isolated it is on the family tree of all birds. The most evolutionarily distinct species are those with the fewest connections and the longest branches separating them from other parts of the tree.

The researchers report that world's top 50 most evolutionarily distinct bird species include widely distributed and common species such as the osprey and the ostrich, well-known oddities such as the hoatzin and the shoebill, and lesser-known, range-restricted species such as the New Caledonian owlet-nightjar and the Solomon Islands frogmouth, the researchers report. The list also includes the South American oilbird and the cuckoo roller of Madagascar, which are both separated from the rest of the avian tree of life by more than 65 million years.

The researchers then used that information to calculate a new species metric, "evolutionary distinctness rarity," or EDR, which relates a species' evolutionary distinctness to the size of its breeding area. Top EDR species include the Christmas Island frigatebird and the kakapo of New Zealand. These are species with large evolutionary information concentrated in very small areas, i.e. cases where even localized disturbance or conservation action could have a large effect on the tree of life.

Although decisions about how to triage the conservation of species are always difficult, they are nevertheless necessary, says Arne Mooers, a coauthor at Simon Fraser University. The new study shows that use of distinctness measures can provide an objective, effective, and economical way to protect evolutionary diversity. This approach may be particularly useful because information about relationships among species is often much easier to come by than detailed ecological assessments, and evolutionarily distinct species can often be found in places that aren't well known as hot spots for biodiversity.

"In the face of global change and limited resources, integration of growing spatial and phylogenetic biodiversity information holds promise for effectively and economically meeting societal biodiversity conservation targets," the researchers conclude.

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Current Biology, Jetz et al.: "Global distribution and conservation of evolutionary distinctness in birds."