- A study led by Stanford University scientists found that conventional surveying techniques have not only led to some Amazon animal populations being underestimated, but have even missed entire species altogether.
- The researchers tapped the expert knowledge of local Indigenous hunters while performing a conventional line transect survey as a control study in order to reach that conclusion.
- The researchers say their results suggest that sign surveys may be the most efficient method for management-oriented studies conducted in large, remote areas, particularly for studies focused on community-based wildlife management.
It’s well known that the Amazon rainforest is one of the most biodiverse terrestrial biomes on the planet, with 30 percent of the world’s species found there. But it turns out it might be even richer in life than we previously thought.
A study led by Stanford University scientists found that conventional surveying techniques have not only led to some Amazon animal populations being underestimated, but have even missed entire species altogether.
The researchers tapped the expert knowledge of local Indigenous hunters while performing a conventional line transect survey as a control study in order to reach that conclusion, which they’ve detailed in an article published in the journal PLOS One this month.
Animals in the remote Amazon are very good at sensing and avoiding humans, while camera traps can break down and are so expensive that only a limited number can be deployed at any given time, according to Jose Fragoso, a biologist at Stanford University and lead author of the study.
These factors can severely limit the effectiveness of traditional wildlife surveys, which generally consist of marking off an area of forest and counting the animals that can be seen, whether they’re sighted by human observers or caught on camera.
Fragoso said he and his team had much greater success in the Amazon rainforest areas of southern Guyana employing a technique called the “sign method,” which estimates animal populations via indirect evidence such as burrows, feces, footprints, and hair — the types of signs Indigenous hunters are trained to look for.
“We were very surprised that so many animals, and in one case a whole species, were undetected using the visual sighting method,” Fragoso said in a statement. “This discovery questions the validity of so many past studies that reported that rural people through overhunting were gravely reducing or extirpating species throughout tropical forests.”
Over the course of three years, Fragoso and a team that included researchers from Oregon State University, Stanford, State University of New York, Syracuse University, Virginia Tech, and Brazil’s Museu Nacional used the traditional sighting or encounter method as well as the sign method during surveys of more than 200 2.5-mile-long trails. Indigenous hunters skilled in tracking and trained by the researchers in sampling methodologies walked more than 27,000 miles during the study.
The results produced using each method were noticeably at odds. The six most important game animals for local communities in the area — species like deer, peccaries, and tapirs — were not encountered in up to 40 percent of the villages or control sites where conventional survey methods were applied, according to the study. Nor were they sighted on 29 to 72 percent of the trails where they were detected by sign.
“Of 32 species analyzed, 31 were detected by both methods,” the authors of the study write, “however, encounters did not detect one and under-detected another 12 of the most heavily hunted species relative to sign.”
Using the sign method, the authors added, showed that tapirs, a species that is of great cultural importance and yet highly sensitive to overexploitation, are present at many sites where they were never visually detected.
The researchers say these results suggest that sign surveys may be the most efficient method for management-oriented studies conducted in large, remote areas, particularly for studies focused on community-based wildlife management.
The researchers cautioned that even if Amazon animal populations are healthier than previously believed, that does not mean that overhunting is not a problem. In the region where this study was performed, Fragoso said, the locals hunted only for their personal food needs. Areas subject to commercial hunting have seen drastic population declines – such as the many regions in Africa and Asia, for instance, where commercial hunting of elephants and rhinos has driven those species to the brink of extinction.
Conservation of game species must take into account the livelihood and food security needs of local communities, the researchers note in the study. Fragoso hopes his team’s results in Guyana can help prevent such declines in other remote rainforest areas. He stresses that reliable counts of animal populations are key to planning conservation efforts.
“Having an accurate count of animals allows us to set appropriate hunting levels and this increases the likelihood of achieving sustainability in the system,” Fragoso said. “This gives governments and institutions that govern human resource use more options for conserving land and protecting animal species.”
- Fragoso, J.M.V., Levi, T., Oliveira, L.F.B., Luzar, J.B., Overman. H., Read, J.M., et al. (2016). Line Transect Surveys Underdetect Terrestrial Mammals: Implications for the Sustainability of Subsistence Hunting. PLoS ONE 11(4): e0152659. doi:10.1371/journal.pone.0152659