The paperbark trees remember the rain of months ago. Now, in the chill of mid-winter, their creamy flowers are in spectacular abundance. The number of nectar-eating flying foxes at the Byron Bay camp suddenly increase. How do they all know this blossom fest is on?
Grey-headed flying foxes Pteropus poliocephalus are great travellers. In 2012, Billie Roberts and colleagues tracked 14 adult males for about 25 weeks on the Australian east coast. These animals moved 50–100 kilometres a night, sometimes even 300 kilometres a night. All up, they covered an area over 1,000 kilometres long and 128 kilometres wide.
These males visited 77 roosts and, 64 per cent of the time, they stayed there for less than five days in a row. So more often than not, flying foxes live outside of our human routines of home-making and commuting. This is why they seem to defy our frantic efforts to ‘cull’ or ‘relocate’ any single camp.
Flying foxes live life large across the landscape. They are the chief pollinators and seed carriers for many species of forest trees. They soar over all those young trees planted out by the Landcare groups and bush regeneration teams. A healthy individual only lives 15–25 years, so their offspring will be the ones who will tend these forests of the future.
Their biology is mysterious. The bare facts of their lifecycles are known. Adults are monogamous and mate all year round. But the males are only fertile during April and May. In October and November, females give birth to live pups. They breastfeed and carry the babies for three weeks. By three months of age the young can forage on their own but they aren’t weaned until about six months of age.
But the immune systems of bats work quite differently from those of humans or other mammals.
Michelle Baker, from CSIRO, thinks that the changes are brought on by the energy demands of flying. Bats use a lot of energy, which leaves them with high levels of toxic oxidants in their tissues. They cope by changing some of their DNA repair systems.
Unexpectedly, this has a beneficial spin-off for them. For humans, understanding this process may lead to a breakthrough for better antiviral medicines. The biochemistry of bats evolved an immune system that is constantly revved up against viruses.
The urban bat
Although bats carry heavy loads of different viruses, they have no symptoms of diseases that can kill the rest of us plodding mammals. Over centuries, as their forest roosts and travels were secure, they coped well enough. Apparently, so did the humans who hunted them for food.
But destroying forests and converting them into paddocks full of domesticated animals forced flying foxes into new living arrangements. They must live more closely with new neighbours. Being clever mammals, they urbanised, roosting in towns and cities. Sensitive to extreme heat, they have shifted their range south by some 450 kilometres.
Not only their lives but their deaths are deeply linked to human activity. In 2012, Tidemann and Nelson investigated the life expectancy of 21st-century flying foxes. Over 30 per cent die from heat stress, almost 20 per cent from electrocution with power lines and another 10 per cent from tangling in nets and barbed wire.
On top of this, the NSW government still licenses shooting these endangered animals as well as ‘dispersals of camps’. The language itself should make Australians shudder.
By 2030, the species may be functionally extinct. Some groups of animals may be seen but not enough will be alive to be effective pollinators of the forests – just when all those trees planted by Landcare and bush regenerators finally grow up.
What if we get into action about global warming and take reforestation seriously? Will we need to create sanctuaries and breeding programs for forest pollinators too?
Flying foxes have excellent vision and hearing. Researchers understand at least 20 different vocalisations that the bats use to communicate among themselves. Likely their culture, as that of many mammals, is subtle and relies on elders to teach youngsters. Perhaps these elders would teach us too.