Nav: Home

Aerial surveys of elephants and other mammals may underestimate numbers

October 31, 2016

AMHERST, Mass. - As lead researchers in Africa's recent Great Elephant Census, wildlife ecologists Curtice Griffin and Scott Schlossberg at the University of Massachusetts Amherst, with Elephants Without Borders director Mike Chase, also evaluated elephant counting methods in the wild. In a paper this month in PLOS ONE, authorssuggest that the two main census methods now in use may be undercounting elephants and that population estimates from both are biased low.

"Because factors such as observer and habitat affected detectability of elephants, comparisons of elephant populations across time or space may be confounded," they write. They encourage survey teams to incorporate "detectability analysis" in all aerial surveys for mammals and suggest that researchers "should assume that their results are biased low by at least 10-15 percent and possibly more." More study is needed to determine the amount of undercounting for other species and factors affecting their detectability, they add.

Griffin, Schlossberg and Chase used the most accurate, up-to-date survey and statistical methods to analyze data for the two-year, $8 million African census funded by philanthropist Paul G. Allen. Despite possible low population estimates, census results reported in August confirmed massive declines in elephant numbers over the last decade, including an annual 8 percent species decline rate, mainly due to poaching.

Griffin and colleagues point out, "Accurate counts of animals are critical for prioritizing conservation efforts. Past research, however, suggests that observers on aerial surveys may fail to detect all individuals of the target species present in the survey area. Such errors could bias population estimates low and confound trend estimation."

To address this, they used two approaches to assess the accuracy of aerial surveys for African savanna elephants in northern Botswana. With the first, double-observer sampling, two observers make observations on the same herds to determine if elephant herds are being missed by observers. Griffin says, "You would think that an animal as big as an elephant would be easy to spot from a plane, 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."

In the second part of their study, they used a helicopter for a total count of all elephants in study areas to compare to their sample counts from fixed-wing aircrafts. Overall, total counts were not statistically distinguishable from sample counts, but they reported that observers typically detected about 76 percent of elephant herds and 87 percent of individual elephants present in survey strips. They concluded "that our population estimates based on sample counts were approximately 13 percent below the actual values."

"These findings are consistent with past research indicating that observers on aerial surveys miss some large animals," Griffin and colleagues add. "Even animals as large as elephants are not all detected."

The authors add that "undercounting is important to recognize because imperfect detectability can induce spurious trends in time series," and concerns about changes in detectability "are not merely hypothetical."

They cite a recent antelope study where a population decrease coincided with a drop in herd size that "likely reduced detectability." Similarly, for elephants in Africa, "biased trend estimates could hinder conservation and lead to misallocation of resources. Thus, assessing elephant detectability and correcting counts for vegetation, observers, herd size and other factors should become a standard part of survey protocols."
-end-


University of Massachusetts at Amherst

Related Elephants Articles:

Elephants' 'body awareness' adds to increasing evidence of their intelligence
Asian elephants are able to recognize their bodies as obstacles to success in problem-solving, further strengthening evidence of their intelligence and self-awareness, according to a new study from the University of Cambridge.
African elephants may be the shortest-sleeping mammals
African elephants in the wild sleep an average of two hours a day and regularly go nearly two days without sleep, according to a study published March 1, 2017 in the open-access journal PLOS ONE by Paul Manger from University of the Witwatersrand, South Africa, and colleagues.
Study reveals 'nightmare' for Central Africa's forest elephants
Forest elephants living in an area that had been considered a sanctuary in the Central African country of Gabon are rapidly being picked off by illegal poachers, who are primarily coming from the bordering country of Cameroon.
Poaching drives 80 percent decline in elephants in key preserve
Forest elephant populations in one of Central Africa's largest sanctuaries have declined between 78% and 81% because of poaching, a new Duke-led study finds.
Aerial surveys of elephants and other mammals may underestimate numbers
As lead researchers in Africa's recent Great Elephant Census, wildlife ecologists Curtice Griffin and Scott Schlossberg at the University of Massachusetts Amherst also evaluated elephant counting methods in the wild.
Equality, more than dominance, defines Asian elephant society
A new study on Asian elephants led by Colorado State University found that Asian elephants, unlike African savanna elephants, do not exhibit clear dominance hierarchies or matriarchal leadership.
The Great Elephant Census reports massive loss of African savanna elephants
Results of the two-year, $8 million Great Elephant Census of African savanna elephants led by Elephants Without Borders were released today at an international wildlife conference in Hawaii, confirming massive declines in elephant numbers over just the last decade.
The Great Elephant Census reports massive loss of African savanna elephants
Paul G. Allen's Vulcan Inc. today announced the results of the $7 million, three-year Great Elephant Census, the first-ever pan-African survey of savanna elephants using standardized data collection and validation methods.
Study documents a lost century for forest elephants
Because forest elephants are one the slowest reproducing mammals in the world, it will take almost a century for them to recover from the intense poaching they have suffered since 2002.
Desert elephants pass on knowledge -- not mutations -- to survive
Despite reported differences in appearance and behavior, DNA evidence finds that Namibian desert elephants share the same DNA as African savanna elephants.

Related Elephants Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Changing The World
What does it take to change the world for the better? This hour, TED speakers explore ideas on activism—what motivates it, why it matters, and how each of us can make a difference. Guests include civil rights activist Ruby Sales, labor leader and civil rights activist Dolores Huerta, author Jeremy Heimans, "craftivist" Sarah Corbett, and designer and futurist Angela Oguntala.
Now Playing: Science for the People

#521 The Curious Life of Krill
Krill may be one of the most abundant forms of life on our planet... but it turns out we don't know that much about them. For a create that underpins a massive ocean ecosystem and lives in our oceans in massive numbers, they're surprisingly difficult to study. We sit down and shine some light on these underappreciated crustaceans with Stephen Nicol, Adjunct Professor at the University of Tasmania, Scientific Advisor to the Association of Responsible Krill Harvesting Companies, and author of the book "The Curious Life of Krill: A Conservation Story from the Bottom of the World".