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:

Capturing elephants from the wild hinders their reproduction for over a decade
Capturing elephants to keep in captivity not only hinders their reproduction immediately, but also has a negative effect on their calves, according to new research.
Sisters improve chances of reproduction in Asian elephants
Researchers at the University of Turku found that the presence of a maternal sister was positively and significantly associated with annual female reproduction in a population of working elephants in Myanmar.
Future of elephants living in captivity hangs in the balance
Scientists at the University of Sheffield and University of Turku are looking at ways to boost captive populations of Asian elephants without relying on taking them from the wild.
Wildlife tourism may negatively affect African elephants' behavior
Increasing numbers of tourists are interested in observing wildlife such as African elephants, and income generated from tourism potentially aids in the protection of animals and their habitats.
Sex differences in personality traits in Asian elephants
Scientists from the University of Turku, Finland, have found that male and female Asian elephants differ in their personality.
New welfare tool to help improve the lives of elephants in human care
Zoos and safari parks in the UK are using a special new tool to help them more successfully monitor the wellbeing of elephants in their care, thanks to a study led by The University of Nottingham.
Elephants take to the road for reliable resources
Landscapes can change from day-to-day and year-to-year, and many animals will move about according to resource availability.
Change of teeth causes yo-yo effect in elephants' weight
The weight of elephants living in zoos fluctuates over the course of their adult lives in cycles lasting around a hundred months, researchers at the University of Zurich have found.
Asian elephants could be the maths kings of the jungle
Asian elephants demonstrate numeric ability which is closer to that observed in humans rather than in other animals.
Not so fast: From shrews to elephants, animal reflexes surprisingly slow
While speediness is a priority for any animal trying to escape a predator or avoid a fall, a new study by Simon Fraser University researchers suggests that even the fastest reflexes among all animals are remarkably slow.
More Elephants News and Elephants Current Events

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

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#538 Nobels and Astrophysics
This week we start with this year's physics Nobel Prize awarded to Jim Peebles, Michel Mayor, and Didier Queloz and finish with a discussion of the Nobel Prizes as a way to award and highlight important science. Are they still relevant? When science breakthroughs are built on the backs of hundreds -- and sometimes thousands -- of people's hard work, how do you pick just three to highlight? Join host Rachelle Saunders and astrophysicist, author, and science communicator Ethan Siegel for their chat about astrophysics and Nobel Prizes.