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Bat and Man

Bats live long and well, if allowed and out of the light

Did bats figure in your Hallowe’en? They neither relate much to the Bat Man super-paradigm nor to the spooky, ghoulish, symbols of death that Hallowe’en stories would have you believe.

Instead they may hold the key to eternal youth. This was one of the topics discussed at the ninth Irish Bat Conference held in October.

The trend for many mammals is to ‘Live fast and die young’. Small animals with a high metabolic rate (e.g. mice) tend to have short (and exciting) lives. Larger animals with a slower metabolism tend to live longer. However, bats seem to turn this rule upside down. Bats have an extremely high metabolic rate when flying, but are very long-lived – and don’t seem to suffer from age-related illnesses such as arthritis. Professor Emma Teeling and her team in UCD have been working on bats, and trying to unravel the secrets of healthy old age.

One theory is that something weird is happening with bats’ telomeres. Telomeres are caps at the ends of our chromosomes, which prevent the chromosome deteriorating, or fusing with other chromosomes. They act like the bits of plastic on the ends of your shoelaces – stopping the shoelaces, or genes – from fraying. In humans, these telomeres get shorter with age. However with bats the length of the telomeres seems to shorten and lengthen – and it is not age related. Is this the bats’ secret – for eternal youth?

Or perhaps it’s autophagy – where our bodies break down and clear out dysfunctional cells. Our ability to do this decreases as we age. But this doesn’t seem to happen with bats – perhaps because flight puts an oxidative stress on a bat, and they have developed a better system for clearing cellular damage. Or is it their gut micro fauna? Emma Teeling and her team have captured bats to study these processes .And the studied bats are well loved; every captured bat also gets a feed of a mealworm to make up for the temporary inconvenience of being handled by a human.

And how do humans interact with bats? A presentation by Christian Voigt from Berlin spoke about the effects of human activity on bats. He looked at three types of human activity – farming, wind power generation, and lighting.

Using bat detectors, he studied farmland in Germany, and found that bats prefer complex landscapes to monocultures. Small ponds and lakes were very important, as are edge structures – basically, the more types of habitat you have on your farm, the more species you will attract. Studies by Dr Danilo Russo looked at the economic value of bats to farmers. He tracked bats and found their highest feeding activity was where cows were resting. They appear to eat midges and mosquitoes which prey on the cattle, causing loss of weight to the cows and decreased milk production. As herd size increases, so does bat activity – until the herd size reaches 60. He proposed that cattle are kept near large maternity roosts, and that farmers should do all they can to encourage bats (natural pest controllers) on their lands. Russol also suggested using DNA analysis of bat droppings to look for pests before they actually turn up on the farm – the bats may be keeping the pests at bay, and looking at the droppings could provide an exciting warning system which would alert us to the presence of specific pests before they have a chance to multiply uncontrollably.

The intrepid Christian Voigt tagged some Noctule bats and we watched in horror some footage of bats flying through wind turbines. In Germany 10-12 bats are killed annually per turbine, in the absence of mitigation. So, officially 250,000 German bats are killed every year – but Voigt is not persuaded. He claimed it is an underestimate, as it is based on the numbers of carcasses found per turbine. His own studies show that the problem is not just direct collision, where you find the dead bat on the ground. Rather the most common cause of death is fractures. Indirect collisions, turbulence and changes in pressure causes barotrauma, where blood fills the abdomen, thorax, or lungs and ruptures ears and eyes. The bat may survive a few days, but will ultimately die, away from the turbine. Its carcass is rarely detected by those who monitor these things. Sadly, while at least the tagged male bats seemed to avoid turbines, female bats seemed to be attracted to them, perhaps sweetly thinking they were trees. Christian Voigt flew drones at wind turbines to monitor the turbulence caused by them, and detected wind turbulence both in front of, and behind, turbines, stretching as far as 600 metres from the turbine.

Given the suspiciously low level of post-construction monitoring of windfarms in Ireland, our windfarm developments could have a serious effect on our bat population. And bats are slow to reproduce. Most bats, even fit ones, have one young every one-to-two years.

Light pollution – light – can have a seriously detrimental effect on wildlife. Dark Skies projects are being set up throughout the world to encourage black ways (as opposed to green ways or blue ways) – dark areas, for nature. However, light pollution can also have serious health impacts for people. High light levels in cities affect our Circadian rhythm, causing sleep disturbance, which can lead to depression. Astronomers also campaign for dark skies.

Light pollution on the Mullingar Greenway

Predictably, bats are particularly sensitive to light. One consequence of too much light is loss of roost. If a roost is illuminated, some species of bats may be unable to use it. Bats such as Daubenton’s, Natterer’s and Whiskered are very sensitive to light pollution. A study by Alison Fure (2006) found Daubenton’s bats sensitive to light levels as low as 1 lux.

Another downside is delayed emergence from roost. Bats sample the light at their roost before coming out. If the light levels are high, they will not emerge. However, most insects are found shortly after dusk, so if the poor bats emerge late, they miss their optimal feeding time.

Lighting also causes loss of feeding and commuting routes. Some species of bat – most notably Daubenton’s and lesser horseshoe bats – avoid bright areas. Lighting of a bat-commuting area, for example a river, may prevent them from travelling from a roost to a feeding site. Bats may waste precious time and energy flying longer routes to their feeding areas, and in extreme cases may be unable to feed or roost in their preferred location.

And of course, lights attract insects. Moths and other insects are attracted to the ultraviolet spectrum in streetlight. Some species of bats are semi-tolerant of light, and may feed on the insects found under the streetlights. However, insects are drawn from dark areas, and bats which are sensitive to light may find that their food supply is reduced. So bats are first blinded, then left hungry.

This graph shows the spectrum of light seen by the elephant hawk moth. It can detect colours at light levels which are equivalent to starlight

But enough of the doom and gloom. Some exciting bat-conservation projects are taking place in Ireland. The Vincent Wildlife Trust has teamed up with Limerick farmers to protect lesser horseshoe bats. These bats are extremely rare. Only somewhere between 9500 and 14000 bats are left in Ireland. And there are two populations, one in the Galway/Clare area and one in the Cork/Kerry area. The concern is that inbreeding will occur, unless the two populations are linked. So, in a giant speed-dating exercise, farmers in Limerick propose to adapt their farms to allow the two populations to hook up.

Dr Kate McAney hatched an ambitious plan to link the populations by providing transition roosts – which look like stone pumphouses or large dog kennels on legs, and farmers will erect them and monitor them for bat usage. This fantastic plan could save the species in Ireland.

And then there is the amazing monitoring work being undertaken by Bat Conservation Ireland – they always need volunteers, so if you thing you could be a bat person and can spare an evening or two every summer –

We are living in the time of the sixth extinction, with half our global wildlife population lost since 1970. Bats and Hallowe’en are not things to be frightened of. The real fear is that we will lose our bats entirely – and all the secrets they hold.


Donna Mullen is an ecologist and a founder member of Bat Conservation Ireland