Spotlight Africa: As with humans, turning 50 is a big deal for elephant matriarchs
In the terrible 2009 drought that precipitated our collaboration with the International Fund for Animal Welfare to begin our social disruption study, the Amboseli Elephant Research Project recorded the deaths of half of the Amboseli elephant matriarchs.
Even more tragically 85% of the “old ladies,” aged 50 years and older, died. Amboseli Elephant Research Project followed these females for almost four decades.
It was a devastating time for the research team and devastating too for the elephant families who lost these leaders that had guided family decisions. Some of these, such as the famous Echo of the EBs, had led their families for as long as they had been known to Cynthia Moss and the research team.
In all, 31 of our 62 families lost their matriarchs, and many of those families lost more than one adult female. The worst hit family, the BBs, lost seven adult females, changing everything for the survivors. Of course, the death of old females is inevitable in elephant family life but the rate of these 2009 losses was unprecedented. Even females who are not matriarchs guide their daughters and younger sisters especially during the periods when families split into smaller units to forage when food becomes scarce.
Two years on, and the surviving elephants and the ecosystem are recovering, and we are beginning to document some interesting shifts in the ways that elephants associate with one another. Our baby boom is keeping us very busy; so much so that sometimes I feel as though I’m barely keeping pace. The elephants have spent the past two months or so in very large groups of two or three hundred, which are wonderful to watch but do limit the amount of time I can spend with the study families.
A few weeks ago I did manage to get some time with one of the IFAW study families, the AAs, who had decided that they’d had enough of being mixed in with so many other families and had returned to their usual haunt at the edge of the Enkongu Narok swamp, on the west side of the park. They have six new calves so far in the family and I had been keen to spend time with them to see how these births had affected the dynamics between the three remaining big females in the family: Alison, Agatha and Amelia.
Alison’s latest calf was born on the 25 January, a robust male. As I wrote some notes in my family book (the precious notebook where I keep track of births and deaths and interesting family events), I noticed Alison’s birthdate. Elephants who were born before the start of the study in 1972 are assigned a January birth month, as an official birthday. Since Alison was born in 1962, she had just had her official 50th birthday.
Quite apart from the wow factor of being in the presence of an animal that has lived for half a century, turning 50 is a big deal from an elephant biologists’ point of view. Although we measure and track age continuously (i.e. we have exact numbers calculated from birth date e.g. 12.4 years old), we also group elephants into age classes when examining our research questions, for two main reasons.
First, we want to examine age-related changes according to biologically significant categories. It’s easy to understand that a female in her teens is not the same as one in her thirties for lots of biological and social reasons relating to her individual experience, her reproductive history and her relationships with the other elephants in her family, bond group and clan. It therefore makes sense to group animals in age classes for some of our analyses, to explore changes between different life history stages.
The second reason relates to placing the Amboseli Research Project’s data into the wider framework of understanding elephants and elephant biology. Amboseli is the longest-running elephant study in the world, ever. Most study populations do not have exact birth dates for the adults in their population but our data from the Amboseli study make it possible for elephant ages to be estimated in other populations. It’s important that we can provide age estimates for all populations to compare differences among them and to understand the wide variability that elephants show in their behaviour and ecology across their range.
The most reliable way to assign an age estimate to an elephant is to look at an individual’s teeth. Unlike humans, an elephant’s adult teeth do not erupt all at the same time. In your own lifetime, you will lose your milk teeth and develop a full set of adult teeth in a process that lasts five or six years, beginning around your sixth birthday (and we all remember the fascinated joy with which children go through this process!). Humans have two premolars and two or three full molars (depending on whether you develop wisdom teeth).
Elephant teeth are different. Most obviously, the incisors (the front biting teeth) in elephants have evolved into a pair of tusks, used for feeding and fighting; and, unfortunately, these modified incisors have generated an on-going and escalating tragedy for elephants across Africa and Asia as ivory poaching decimates populations. Elephants have six sets of molars in each jaw quadrat (two upper, two lower), which develop sequentially. While one tooth is in wear, the new tooth is forming in the jaw hinge, and as it grows, it moves forward along the jaw, pushing out the old tooth (worn flat from chewing tough plant fibre), which falls out in small pieces as it reaches the front of the jaw. Through examining which teeth are in wear it is possible to estimate the age of an elephant and at Amboseli we have measured and examined elephant teeth for over thirty years, using data from known-age animals to refine the published age-scales. Other elephant researchers therefore use Amboseli data to help them assign age estimates to individuals in less well-studied populations.
Obviously getting close to an elephant’s teeth is not easy, and requires that the elephant is either immobilised (e.g. during the fitting of tracking collars or veterinary care) or dead. For that reason, most age estimates are done using cues of body size and body proportions. This process is quite easy to learn for younger elephants and notoriously difficult for older ones. Researchers might assign, for example, an age estimate of 35 to 40 years old for a middle-aged female. This degree of uncertainty in the age estimates for many elephant population also makes it useful to group similar-aged individuals together during analyses.
Research in the Amboseli elephants has shown that older females are important social centres for their families, but we can only do this kind of work by following elephants like Alison over the course of her long lifetime. Alison’s decades of experience have and continue to stand her family in good stead.
The goal of our work in Amboseli is to assure that our decades of experience and discovery stand others in good stead as they work to protect elephants across the world.
Help the International Fund for Animal Welfare protect elephants like these from the cruelty of the ivory trade, say "NO!" to ivory right now by adding your name to our online petition.