Credit Michael Fay/National Geographic Image Collection
Africa’s elephants are widely loved — and widely endangered. Poachers killed off nearly 30 percent of the continent’s savanna elephants from 2007 to 2014, according to a survey published this week. Their populations are now declining at a rate of nearly 8 percent a year.
But there are actually two species of African elephants. Savanna elephants roam grasslands in east and southern Africa. The more diminutive forest elephants, only recently recognized as a distinct species, live in dense central and western jungles.
The new survey, called the Great Elephant Census, did not attempt to track forest elephants, mostly because they cannot been seen from the air. But other research shows their plight to be as desperate as that of their savanna cousins. Illegal killings of forest elephants for their tusks drove a 62 percent decline in their numbers from 2002 to 2013, according to one estimate.
Unfortunately, the species will not be rebounding any time soon. As reported in The Journal of Applied Ecology, forest elephants turn out to be one of the slowest reproducing mammals on Earth. Even if all poaching ceased immediately, researchers calculate that it would take 90 years for forest elephant populations to return to pre-2002 levels.
“We already knew about the scale and severity of poaching, but what was not known before was the long-term ramifications of that poaching,” said George Wittemyer, an ecologist at Colorado State University and an author of the study. “This paper shows that things are substantially worse than we expected for forest elephants in terms of how fast they can rebound.”
The findings are the result of nearly 25 years of monitoring. In 1990, Andrea Turkalo, a scientist at the Wildlife Conservation Society, began observing forest elephants at Dzanga Ndoki National Park in the Central African Republic.
Dense vegetation typically makes the elephants nearly impossible to study, but Dr. Turkalo found that they regularly congregated at an open river bank near a mineral lick. She relied on distinctive markings to identify and track 1,200 elephants over time, noting things like growth rates, births and missing individuals.
She and her colleagues at first assumed that forest elephant reproduction would mirror that of savanna elephants, which begin giving birth around age 12 and at intervals of four years.
Instead, the scientists were surprised to find that forest elephants start reproducing on average at 23 years old and only at five-year intervals. Their average lifespan is an estimated 60 years.
Ecology, rather than biology, may be to blame. In dense jungles, productivity depends on the canopy: Animals on the ground must largely subsist on what drops from the treetops. This ultimately limits the amount of nutrients available to fuel growth and reproduction.
Dr. Wittemyer and his colleagues also do not know if their findings apply to all forest elephant populations, though they suspect so.
“We’re hoping to start piecing the puzzle together and glean more information about these animals,” he said. “Not the least because it’s hard to get motivation and political will to protect things we don’t see or know much about.”