Study finds extremely slow reproduction rate unable to keep pace with deaths
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. Not only does it take more than two decades for female forest elephants to begin reproducing, they give birth only once every five to six years.
These are the findings from the first-ever study of forest elephant demography just published in the Journal of Applied Ecology.
There are two species of elephants in Africa. Savannah elephants make up the majority across the continent with smaller numbers of the more diminutive forest elephants restricted to the tropical forests. Forest elephants have experienced serious poaching, driving an estimated population decline of 65% between 2002 and 2013. Their reported low birth rates mean that it will take forest elephants at least 90 years to recover from these losses, according to researchers from the Wildlife Conservation Society, the Cornell Lab of Ornithology's Elephant Listening Project, Colorado State University, and Save the Elephants.
The team used decades of intensive monitoring data that recorded births and deaths of the elephants using the Dzanga Bai in Central African Republic, part of the UNESCO World Heritage Sangha Trinational area.
"This work provides another critical piece of understanding regarding the dire conservation status of forest elephants," said Andrea Turkalo, the Wildlife Conservation Society scientist who over several decades collected the detailed data on the Dzanga elephants despite tough logistical challenges and political instability.
Using data Turkalo collected from 1990 to 2013 during nearly daily visits to a mineral rich forest clearing, or bai, that attracts elephants and other wildlife, the authors were able to uncover the age at which the forest elephants had their first calves, the length of time between calves, and other behavioral observations. The results revealed that forest elephants begin breeding later and have much longer calving intervals, meaning their population takes much longer to increase--information revealed only through this sustained and meticulous research effort.
According to Turkalo: "Female forest elephants in the Dzanga population typically breed for the first time after 23 years of age, a markedly late age of maturity relative to other mammals. In contrast, savannah elephants typically begin breeding at age 12. In addition, breeding female forest elephants only produced a calf once every five to six years, relative to the three to four-year interval found for savannah elephants."
The authors speculate that the low birth rate is due to the challenges of living in a tropical forest, where new plant growth is mostly limited to the canopy.
"While we think of tropical forests as incredibly productive areas, most production occurs in the high canopy inaccessible to ground-dwelling species. In addition, vegetation in tropical systems is laden with compounds to defend their leaves from herbivores. This means accessing resources is challenging for terrestrial fauna," stated Dr. Peter Wrege of the Cornell Lab's Elephant Listening Project.
"This information is essential to assessing the species status and projecting population decline in the face of illegal killing," said George Wittemyer, Chair of the Scientific Board of Save the Elephants and a professor in Wildlife Conservation at Colorado State University. "Legislation regarding ivory trade must consider the collateral effects on forest elephants and the difficulties of protecting them. Trade in ivory in one nation can influence the pressures on elephants in other nations."
The paper's findings show that the forest elephant is particularly susceptible to poaching, vital information for debates and upcoming policy legislation regarding the legality of ivory trade to be decided at the IUCN World Conservation Congress and the Convention on International Trade in Endangered Species (CITES) conference in September.
The authors also highlight the importance of their results for interpreting carcass data collected through the Monitoring of Illegal Killing of Elephants program, which have shown terrible levels of poaching across central Africa.
"Only by understanding the basic biology of forest elephants and other species, can we properly determine the level of threats they face from human activities," said Wittemyer.
Failing to protect forest elephants would also damage Central African forests, which are vitally important for absorbing climate change gases.
Forest elephants have critical ecological roles in these forests, and many tree species rely on the elephants to disperse their seeds. Continued decline in forest elephant numbers and range is likely to drive severe changes to these ecosystems, making their conservation status a significant global issue.
