by Colin Swider
People are familiar with elephants, even though most people have never seen one in person or in the wild. Elephants are thought of as majestic, charismatic giants that roam the savannas of Africa or the jungles of Asia. When people think of elephants, they usually envision one of the two well-known species- the African savanna elephant (Loxodonta africana) or the Asian elephant (Elephas maximus). Most folks don’t realize that a third, less familiar, species inhabits the rainforests of Central Africa- the African forest elephant (Loxodonta cyclotis).
There are several reasons why this third inconspicuous species remains unknown to most people. For starters, while most experts agree that they are indeed a distinct species, the International Union for the Conservation of Nature (IUCN) has yet to officially classify them as such. Instead, they are classified as a subspeciesof the African elephant. Under this scheme, savanna elephants and forest elephants are considered to belong to the same species. However, morphological, ecological, social, and genetic evidence clearly indicates that forest elephants deserve separate species status, and other institutions, such as the Convention on the Conservation of Migratory Species, already recognize this distinction. In addition to being markedly smaller than savanna elephants, forest elephants also have more rounded ears, hairier trunks, and thinner, straighter, and denser tusks. Forest elephants also have the lowest reproductive rates of the three species.
Perhaps the bigger factor that obscures the visibility (both literally and figuratively) of African forest elephants is their habitat. Unlike savanna elephants, which inhabit mostly open plains and scrublands, forest elephants live in the Congo Basin where dense, lowland, tropical rainforest dominates the landscape. This makes them nearly impossible to observe and study using visual methods. The surveys conducted from planes, helicopters, and jeeps that are so effective for elephants in the savanna are useless in the rainforest. The canopy is too thick to see through from above, and ground vehicles simply cannot penetrate the vast majority of the forests that these elephants call home.
This is where acoustic methods become useful. Forest elephants (and all elephants for that matter) make very low-pitched vocalizations known as “rumbles”.
Forest elephant vocalizations known as “rumbles”. Recording by Elephant Listening Project (Cornell).
These calls travel very far distances and can be detected by microphones and acoustic sensors. Sensors can be attached to trees and left to record sound continuously for weeks, months, or even years at a time. Grids of sensors can be established, covering small patches of forest to entire national parks. These recorders provide us with a continuous record of elephant vocalizations over time and space. By taking advantage of the fact that the animals announce their presence to us through their vocalizations, we bypass the need to survey them visually, which is near impossible in the Congo rainforest. Using these acoustic methods, we can begin to understand the particular types of habitats that are important for the species, and the areas that need further conservation protection.
An array of acoustic sensors in a national park in Cameroon. Inner and outer circles around each sensor represent approximate detection distances for elephant rumbles and gunshots, respectively. Map by C. Swider.
We live in a critical time for the survival of elephants. Forest elephants, with an estimated total population size of less than 100,000 individuals, are more severely threatened by poaching than the other elephant species- as much as 10% of the entire population is killed each year for ivory. It is thus of critical importance to understand patterns and hotspots of poaching so that the effectiveness of anti-poaching patrols can be enhanced. Acoustic methods can be used to understand such patterns, as gunshots are also detected by acoustic sensors. By detecting and analyzing patterns of elephant vocalizations and gunshots, it is possible to gain insights into the environmental factors that influence forest elephants’ habitat use, as well as the threats to their existence.