Counting individual elephants and entire herds from the air sounds like it should be easy enough. After all, how hard could it be to count accurately something so big?
Harder than it sounds, perhaps. A team of ecologists at the University of Massachusetts (UMass) suggests in a new study in the journal PLOS One that African savanna elephant surveys may underestimate their counts of the animal by about 10% to 15%. And, with species survival as well as tourist revenue at stake, conservationists and countries that are home to elephants have plenty of incentive to know just how many animals are roaming a given area.
To check the accuracy of elephant surveys made from the air, the UMass researchers employed so-called "double-observer" sampling, using two observers on one side of an airplane to make independent, simultaneous counts of the same elephant herds and individual elephants. The setup left the scientists with a way to gauge how often both observers saw the same things.
"You would think that an animal as big as an elephant would be easy to spot from a plane," said study co-author Curtice Griffin in a statement. "But factors such as herd size and habitat type can affect the ability of observers to see elephants from a small plane traveling at over 100 miles per hour, 300 feet off the ground."
The team found, using photographs to reconcile visual observations, that the two observers detected 76% of elephant herds and 87% of individual animals.
"Thus," they wrote of the under-counting, "aerial surveys for mammals should assume that their results are biased low by at least 10% to 15% and possibly more."
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"Accurate counts of animals are critical for prioritizing conservation efforts," the scientists noted. Knowing how dire the situation is, or is not, for an animal can impact how conservationists employ their resources.
What's more, having the best information available can have implications beyond ecology. That was evidenced this week, when a report by the International Union for Conservation of Nature determined that elephant poaching costs African countries about $25 million per year in lost tourism revenue.
Elephant conservation, the authors of that report wrote, "is a wise investment decision for countries in the savanna regions of Africa." The more elephants a park boasts, the more likely the site will be to draw visitors. Each additional elephant in a park, they found, boosted tourist visits by 371 percent.
The same study said the African elephant population was down about 30% from 2007 to 2014.
The University of Massachusetts researchers offered suggestions for counts of elephants and other animals going forward.
"In the future," they wrote, "we suggest that aerial surveys for large mammals incorporate some type of detectability analysis into their methods wherever possible. Even if only a single aircraft and two observers are available, both observers can sit on the same side of the plane and conduct double-observer trials."
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