But it appears that if we could just tune into a different register and home in on the sounds at the very limits of hearing, we would be almost deafened by the resulting cacophony.

    The team of bat experts which was haunting the waterways of Crom Estate for four nights last week found their detectors rarely stopped clicking.

    In fact, the night skies of Crom are so rich with the airborne mammals that it has been recognised as one of Ireland’s richest habitats for bats.

    As they prepared to carry out last week’s landmark survey, scientists had already been expecting spectacular results, but only two weeks ago Northern Irish bat expert Mark Smyth discovered Crom was home to one bat that had never previously been observed there - the Natterer’s bat.

    Mark and his colleagues in the Northern Ireland Bat Group had been working hard at Crom in the weeks running up to this survey and discovered that all eight species of bat found in the Province make their homes at Crom.

    Until recently scientists believed the Nalthusius bat was extremely rare in the UK but a colony has been found breeding in Coleraine and the bat also appears to be present at Crom. Only nine species of bat are found in Ireland, compared to 16 in Britain, so to find eight species at Crom was very exciting for the National Trust wardens who work there.

    Even the names of the tiny nocturnal animals are weird and wonderful - as well as the Nalthusius bat, there’s the soprano pipistrelle, the common pipistrelle, Leisler’s bat, Daubenton’s bat, the Natterer’s bat, the whiskered bat and the brown longeared bat.

    One of the best ways to tell bat species apart is to record their calls.

    Lucy Cordrey, nature conservation technician with the National Trust, transfers the bat cries onto computer, turning sound into visuals with a programme called a spectrogram.

    The calls on the chart are of different frequencies, with perhaps several short sharp clicks tailing away, or a longer cry - but the shape and frequency of the call is highly characteristic of the species.

    Slowed down to the level of human hearing, the squeaks we can normally make out are transformed into a jungly-sounding symphony, very like tropical birdsong, Lucy says.

    Members of the team that converged on Crom last week included volunteers from Northern Ireland Bat Group, nature conservation experts from the Northern Irish and national wings of the National Trust and consultant and bat expert Geoff Billington from England.

    Dr David Bullock says Ireland is internationally important for Leisler’s bat.

    “The reason we came to Crom is that we suspect it is one of the most important places for bats in Ireland,” he says.

    “The critical thing here is the woodland and the water next to it and the buildings providing roost sites as well.

    “On the basis of what we have found over the last few weeks, Crom is fantastic for bats in a British and Irish context.

    “It is rare to go anywhere in Britain or Ireland and find the bat detector ticking away all the time - bats are everywhere here.” Only three sites across the UK have been chosen for these major bat studies and the other two are in northern and southern England.

    The unusual shape of Crom Estate, with tracts of water tucked right in among the woodlands and the many wooded islands where wildlife goes largely undisturbed, is partly what lies behind the flourishing bat populations.

    The combination of water and woods is an ideal habitat for the prey of the bats - insects.

    “Crom is famous for its mosquitoes,” David says.

    The rich panorama of trees, old buildings and walls provide plenty of roosting sites for bats, which can be picky.

    Some favour large breeding roosts, while in other species you may find males roosting singly. The walled garden in particular seems to be a popular residence. The large lofts in Crom’s buildings are favourite roosts for the brown longeared bat.

    David says: “What makes them attractive is that the lofts are very large and for longeared bats that is important. They like to fly around before they come out.”

    This is partly because they are social animals and partly because they check to see whether it’s dark and safe before leaving the protection of the roost.

    “They don’t want to get picked off by a late-flying sparrowhawk,” David explains.

    There are patterns to the different species’ activities and this survey has shed a lot of light on these.

    In the gloaming, as dark starts to fall, the first to emerge from their roosts are the pipistrelles and Leisler’s bat. As it grows darker, the next is the whiskered bat and, later still, Daubenton’s bat, the Natterer’s bat and the brown longeared emerge.

    The bats tend to hunt for a few hours and then rest in a tree during the darkest part of the night.

    This is because insect abundance is greatest at dusk and dawn so there is no point in expending energy at times when there is little food to be found.

    As the sky lightens before dawn, the bats go hunting once again and then seek their roosts in the reverse order to which they emerged - first the Natterer’s and Daubenton’s bats go to their roosts in the dark and the pipistrelles and Leisler’s bat are the last to retire.

    Leisler’s bat feeds high in the sky, hunting large moths, while Daubenton’s bat hunts almost exclusively over the water, skimming low in search of mayflies and midges like a tiny hovercraft and occasionally scooping them from the surface with its feet.

    The team spent last week travelling to different islands and using bat detectors to record the activities of the tiny animals. In addition they caught a number of bats and fitted them with small collars carrying radio transmitters which are later groomed off within a couple of days.

    One Natterer’s bat, for example, was caught, tagged and released on the island of Inisherk and tracked back to his roost in a crack in the wall of the walled garden on the mainland.

    The scientists headed out to the islands by boat at dusk and worked through the evening until finally heading to their beds at 1.30am.

    The lights as they quietly went about their business must have presented quite a mystery to nearby cruisers.

    David explains that this is the time of year when bats are most likely to blunder into your home by accident.

    “This is the time of year when the babies first take flight,” he explains.

    “They may get disoriented and not know which hole they flew out of - they see an open window and fly in through it.”

    If it takes refuge on a curtain, the best thing to do is turn the lights out, put a hanky round the bat and then gently release it outside or place it under the eaves, David says.

    Bats are stringently protected by law and if they cause a problem, the best thing to do is contact the Environment and Heritage Service for advice.

    For the scientists, bats weren’t the only attraction at Crom. They loved the beautiful grounds and caught sight of many other animals, including badgers, goats, fallow deer and a pine marten.

    Although the pine marten is carnivorous it does eat fruit and can sometimes be seen raiding the orchards.

    When the scientists were heading out to one of the islands, they were asked to do one special job. The pine marten has developed a taste for jam and looks forward to the occasional treat.