Life, is ‘poor nasty brutish and short’ said Thomas Hobbes. Certainly, it’s no bed of roses. Natural selection should have equipped us to deal with fear and anxiety, but has it?
Although stress may not kill us directly, it has long-term consequences for our health. People who endure Angela’s Ashes- style trials and tribulations in childhood are prone to illness later in life. Is this also true of other long-lived species?
Hannah Mumby and colleagues at the University of Sheffield have examined the effects of stress on elephants working in the logging industry of Myanmar. The country, formerly known as Burma, produces three quarters of the world’s teak. About 50% of Burmese people depend on forestry, at least partially, for their livelihood.
Draught horses, a common sight on our streets up to the 1960s, used to pull barges along the canals. In Myanmar, elephants spend their days dragging and pushing logs down to rivers, to be floated downstream, processed into timber, and exported. About half of all Myanmar logs are moved by elephants. Around 5,000 of these huge beasts, the largest captive population in the world, live in government-owned camps.
Asian elephants, whose wild cousins are classified as ‘endangered’ by the International Union for the Conservation of Nature, are an essential resource. Working animals, however, have low survival rates and produce so few calves that replacements have to be recruited from the wild. The Myanmar Timber Elephant Project, based at Sheffield, seeks to increase the life expectancy and reproductive success of working animals so as to alleviate the pressure on the wild population.
Operators know the value to their elephants. They are given regular health checks and each has its own logbook. Breeding is not controlled; the elephants, in their family groups, can roam the forest and mate with whom they like. Workers are classified as ‘semi-domesticated’, some calves being sired by wild bulls.
Gestation in elephants takes 24 months, the longest of any mammal. Pregnant females are given a year’s maternity leave and then assigned light duties. Calves are cared for by their mothers and ‘aunties’ until they are four to five years old, when training begins. Each one is assigned to an individual carer, known as an ‘oozie’, its relationship with whom may last a lifetime. Until it is 17 years old, an elephant will engage in light work. Then the heavy lifting starts.
The Sheffield scientists have access to records of births and deaths for over 10,000 working elephants, spanning three generations. They have studied behaviour in the field and measured stress hormone levels during the year. The hormone readings show the monsoon from June to August, during which the elephants’ workload is greatest, is the most stressful.
Not many calves are born during these months and their survival prospects are poorer than for ones born at other times. Youngsters whose mothers had previously endured high levels of stress go on to have pregnancies earlier than those born to more fortunate females. However, the reproductive rate of the early breeders falls rapidly and they have fewer offspring.
Being born and raised in adversity increases an elephant’s vulnerability to disease later in life. The ageing process is accelerated and a deprived childhood can affect an elephant’s health decades later.
These results will come as no surprise to zookeepers; elephants are sensitive souls who need lots of tender loving care. Dublin Zoo, which has a herd of eight, is regarded as a world leader in the elephant husbandry field. An Asian elephant expert from Germany, who had spent a week with them, told me that our animals were the most contented she had ever studied. That three elephants delivered healthy babies in just over a year attests to this.
© Irish Examiner Ltd. All rights reserved