Three score years and ten is all that our species gets, according to the Bible, although these days many of us hope to push on a little longer. But for other animals, just how old is old? A quick glance around the African animal kingdom shows that life expectancy does not always meet expectations. By Mike Unwin.
Slowly does it
Tortoises are famed for their Methuselah-like existence, their slow metabolism allowing them to lumber on for longer than any warm-blooded mammal or bird. The oldest known individuals are among the Aldabra giant tortoises of the Seychelles. One individual named Adwaita died at Kolkata Zoo in March 2006 after having first been captured by British seamen in 1875. His shell was carbon-dated to a birth date of 1750, meaning that he reached the impressive age of 255. Today the main population of this species is on Aldabra Atoll, with a smaller population on the island of Changuu, off Zanzibar.
Short and sweet
Lifespans vary wildly among fish. While a whale shark might continue to migrate up and down Africa’s east coast for a century, killifish of the Nothobranchius genus barely last a summer. The latter are colourful, 5cm-long tiddlers that inhabit ephemeral pools on East African savannahs. Their ‘annual’ life cycle effectively boils down to a few frantic rainy season months, until these pools dry up. During this time they hatch, mature, breed, spawn and die, leaving their eggs buried in the dry mud to hatch with the following year’s rains. One species, Nothobranchiidae furzeri, is the shortest-living vertebrate bred in captivity, with a lifespan of just three to six months.
Long in the tooth
Elephants live longer than most mammals, often topping 50 years in the wild. Indeed, with few predators and a supportive social structure, they may reach 70 years or more. Females become sexually mature at 9–10 years, then continue to reproduce until mid-life before undergoing a menopause-like post-reproductive phase. The end comes down to teeth – or, rather, the lack of them. By its mid-40s, an elephant has acquired its sixth and final set, which must last it the rest of its life. Once these molars wear down, it can no longer process the coarse food on which it subsists, and eventually starves to death.
Pretty elderly Polly
The African grey parrot, like many of its kind, enjoys a very long innings. The oldest reliable longevity record from captivity is 49.7 years, although claims of over 90 years exist. This species, which is endemic to the rainforests of West and central Africa, has been prized since the Ancient Greeks for its sociability and intelligence, with doting owners including Henry VIII. Indeed, scientific studies of one individual named Alex have suggested that an African grey can develop the intelligence of a five-year-old child. Wild individuals do not live so long, being vulnerable to predators once they start to slow down. Keep one as a pet, however, and you’d better provide for its future upkeep in your will.
Long live the queen!
Ant society is divided into castes, whose individuals differ not only in size and shape but also in life expectancy. Queens may live longer than 15 years, 100 times longer than most workers. Their longevity is promoted by their lifestyle: larvae destined to become queens are fed ten times more often than others, while mature queens – as befitting royalty – have it cushy, suffering little wear and tear and receiving constant grooming from their devoted minions. A worker’s lifespan is also dependent upon what job it does, with exceptional cases of individuals living over five years. Once a queen’s sperm stock is exhausted she dies quickly, often assassinated by workers, who have no qualms about regicide once their monarch becomes unproductive.
From Travel Africa 64 Autumn 2013