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Why are lists of bird species different around the world

How many types of birds are there in the world? It depends on who you go to. The number can be up to 10,000 or up to 18,000. The lists of species are difficult to standardize because the concept of “species” itself is somewhat vague.

This is important because maintaining biodiversity requires knowledge of the diversity that exists in the first place. So biologists, led by Monty Niet Clegg, a doctoral candidate at the University of Utah, from the School of Biological Sciences, set out to compare four major lists of bird species around the world to see how the lists differ – and why. They found that although the lists agree on most birds, disagreements in some regions of the world may mean that some species have been missed by ecologists.

“Species are more than just a name,” says Neate-Clegg. “They are functional units in complex ecosystems that need to be conserved. We need to recognize true diversity in order to conserve it.”

The results have been published in Global Environment and Biogeography.

On the Origin of Species

The definition of the species is not clear. Some scientists define population groups as different species if they are reproducibly isolated from one another and unable to mate. Others use physical features to define the species, while others use genetics. Using genetic identification results in many species, but regardless of the method, the gray areas persist.

“Species are ambiguous because speciation as a process is not clear,” says Neate-Clegg. “It’s a gradual process so it’s very difficult to draw a line and say ‘These are two types’ vs.. This is one.”

As he says, physical traits and genetic signatures do not always diverge on the same time scale. For example, “he says,” two groups of birds may diverge in song and appearance before genetic difference. Conversely, similar populations on different islands can be separated genetically by millions of years. “

Compare listings

At this point in the story, it is time to introduce four lists, each intended to include all types of birds in the world. they:

  • Howard & Moore List of Birds of the World
  • EBird / Clements Checklist for Birds of the World
  • BirdLife International Watchlist for Birds of the World
  • World Bird List of the International Bird Community (IOC)

“Being active ornithologists in the field and always trying to identify bird species means that one always faces the problem of having some species on one list but not the other,” says Chagan Cekerioglu, associate professor in the College of Biological Sciences. “So our field experience motivated us a lot to ponder this question and inspired us to write this paper.”

Lists have different strengths depending on their application. BirdLife International’s list, for example, integrates with the IUCN Red List, which reports on the conservation status of the species. The International Olympic Committee Ekercioğlu says the list is updated by experts twice a year. The list is open access with comparisons to other main menus, and changes are documented transparently.

“ But as a bird watcher, I use eBird all the time, which uses the Clements checklist and this dataset Very powerful in itselfSo there is no single best option, ”says Neate-Clegg.

The common bird might be one example of a quarrel between rolls Colaptes auratus. Call it the eBird list name Northern Flash, To woodpecker. But BirdLife International’s listing identifies the eastern population as a yellow flash and the western population as a red flash.

In 2020, Neate-Clegg and colleagues read To study Which compared the species of raptors on each list, and found that only 68% of the species were consistent across all four lists.

“We thought it would be interesting to investigate the classification agreement for all 11,000 bird species,” says Nate Clegg. “Most importantly, we wanted to try to identify the characteristics of the species that led to more or less taxonomic confusion.”

They began by collecting the most recent version of each list (the IOC checklist is updated twice a year, researchers write, and the Clements and BirdLife lists annually, while Howard and Moore haven’t been updated since 2014) and shrinking it to exclude subspecies and any extinct species. Using some other data-processing rules, they assigned one name to all possible types across all four lists. Then the comparisons began.

Where the two lists agree and differ

The researchers found that the four lists agreed on the vast majority of bird species – 89.5%. For the remaining 10.5%, they began to look for patterns that might explain the discord. Some of them were likely geographical. Birds from the well-studied Northern Hemisphere were more likely to find agreement than birds from Southeast Asia and the Southern Ocean that had not been well studied.

Some of them were dependent on the habitat. Agreement was higher for large migratory species in relatively open habitats.

“I think the most surprising finding was that the agreement was no less for species that are highly dependent on forests,” says Nate Clegg. “We expected these rainforest residents to be the most mysterious and difficult to study, with more uncertainty about their taxonomic relationships. However, we found that in fact it was the species with medium forest dependence that had the lowest taxonomic agreement. We believe.” That these species move far enough apart, but not to the point where their genes are constantly intermingling. “

And part of the issue of classifying species on isolated islands, such as those in Southeast Asia and the Southern Ocean, there has been a phenomenon called “hidden diversification”. Although islands can enhance species diversity due to their isolation, sometimes two groups of people on different islands can appear very similar, although their genes indicate that they have been isolated from each other for millions of years so, depending on the definition. , Two groups of the population can be considered two species or only one species.

Additionally, Neate-Clegg says, “It is very difficult to test the concept of a traditional biological species on island animals because we cannot know whether two groups can mate to produce fertile young if they are geographically isolated.”

why does it matter

So what if some people disagree over the species’ nomenclature? Neate-Clegg says conservation procedures are usually at the species level.

“If a population on one island becomes extinct, people might not care if it was just a subspecies,” he says. However, that island is likely to lose a unique population functionally. If it is recognized as a complete species, it may not have been lost. “

Neate-Clegg hopes the study will direct ornithologists toward species groups that deserve more attention.

“We also want conservation biologists to realize that hidden diversity may be overlooked, and that we must take into account conservation units above and below the species level,” he adds.

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