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If you regularly post your bird sightings to eBird.org but wonder whether your data is valuable, then Joshua Horns, a doctoral candidate in biology at the University of Utah, has good news for you. In a study about the reliability of eBird data, Horns and his colleagues compared population trends for 574 North American species as shown in eBird data with official trends from the Breeding Bird Survey, conducted annually by the U.S. Geological Survey throughout the United States and Canada.
The researchers, writing in the journal Biological Conservation, examined more than 11 million eBird checklists submitted between 1997 and 2016 and found that observations submitted to the site match trends in bird species populations measured by the government survey to within 0.4 percent.
The finding suggests that birders throughout the world who report their sightings to the website are providing extremely valuable data. Users of eBird are present all around the globe, of course, but official government data about species trends is absent from many places, including South America, the Caribbean, and tropical Africa. Data for individual species in eBird can serve as a stand-in of sorts in the absence of more rigorous surveys.
The question, then, is how many eBird lists are necessary for any one region to closely approximate actual populations?
Horns concluded that to accurately track a species’ population, the minimum was about 10,000 lists. So when a country or region has at least that many lists, the results suggest, you can be confident that population trends observed in the lists are a reflection of reality.
But what about areas that don’t have that many lists? Horns says that lists from bird atlases and trip reports from ecotourism groups can also be used, with list length as a proxy for birder skill.
Read “On the Move,” our migration column featuring distribution maps from eBird
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