Why we should welcome the swallows of the night

ON a muggy day in August the air between the young trees on the acre is positively dancing with flies. Swallows mooching down the coast on migration spot this thicket on the hillside and treat it like a fast-food joint, twittering after midgeburgers. They sometimes swoop in dizzying numbers round and round, so that trying to count past the 51st the other evening, I fell into the carrots.

Once dusk has fallen over Ireland the bats take over from the swallows - even, perhaps, to greater effect, since one little pipistrelle can polish off as many as 3,500 insects in a night. Leisler's bat - our biggest - often comes out early, at sunset or before, and actually mingles with swallows as it hunts over woodland and scrub.

Bats, like swallows, will sip water on the wing, and snatch up flies from the surface of a river or lake. In the current Irish Naturalists' Journal Cork zoologist Paddy Sleeman points up the perils of pipistrelles when anglers go fly-fishing on summer nights. Casting with an imitation sedge, Dr Sleeman knocked a pipistrelle for six and had to rescue it from the water. Another angler hooked a pipistrelle's wing on a wet-fly. Unhooked, it promptly retired within a crevice in a bridge.

One bat story this summer, reported by a Dublin reader, may be more typical of the hazards befalling these much-misunderstood creatures, notwithstanding a favourable press and protection under the Wildlife Act.

It begins with a cat bringing home dead Leisler's bats to a house in the city suburbs. The cat's owner, concerned, contacted the local bat group. They discovered a nursery roost in a neighbouring house where repairs were being done on the fascia boards.

The workmen, completing a thorough job with silica gel, had sealed off the bats from their young inside the roof space. One of the adults was stuck in the gel; others clung to the boards while their babies called from within. Eventually, after a day's negotiation with a remarkably indifferent houseowner, one of the group was allowed to nick a hole in the gel, through which the bats could rejoin their babies and suckle like ourselves. Being tiny, gymnastic and airborne. they cannot afford to be burdened by heavy embryos, so they tend to give birth early and nurse for a long time. The pipistrelle, for example, our smallest and most abundant bat has a 44-day pregnancy and nurses her single offspring, born in June or July, for almost as long again.

Leisler's is not only our biggest bat but probably the most important one ecologically. It is an endangered species in Europe, and Ireland, tucked away at the northern edge of its range, now holds its largest populations. The biggest known roost in the world is a breeding colony in West Cork with up to 1,000 bats.

Leisler's seems to prefer attics to trees for its summer roosts. Dr Patrick O'Sullivan, who led a survey of Ireland's bats for the Wildlife Service, noted that this one his inquisitive, and will hang down, extending its neck to investigate disturbance. Occasionally it lands on the intruder, a habit unique to this species."

Is it necessary to reiterate that bats really don't get caught in women's hair? Empirical evidence in the matter was offered by the Earl of Cranbrook, a bat enthusiast. in 1969. At a summer dinner party in his Suffolk home. the earl - or perhaps the butler - used a butterfly net to catch a pipistrelle that had flown through the open French windows.

"Struggling, squeaking and biting furiously, it was obviously a better subject for experiment than the tame one I had in a cage, so I lifted up a handful of Mary's curly hair and popped the bat in. I had done, the same with four different species of bat and the blondes, and the earlier results were repeated: the pipistrelle scrambled up over the top of Mary's head without getting entangled in any way and took flight out of the door, back into the night."

Pipistrelles are, however, the species which seems to cause the public most problems. They like to pack together in very confined spaces behind window sashes, under tiles and weather board, behind fascia boards and within the cavities of flat roofs, and they can squeeze through a hole no bigger than a thumbnail. They can be a bit smelly, they often squeak a lot in warm weather, and they make scratchy noises on the other side of the ceiling. It needs only one or, two to stray out of bounds and people start having hysterics.

The long-eared bat is another attic rooster, but usually in small, numbers, clustered closely together under the roof ridge. It prefers a spacious, open attic, rather like the lesser horseshoe bat, which is most at home in the big houses and castles of the west.

The lesser horseshoe (named for the shape of its noseleaf) is the only one of Ireland's seven species which actually hangs down freely from horizontal surfaces (the little Natterer's bats in my woodshed, for example, wedge themselves invisibly into crevices in the corrugated roof).

The lesser horseshoe spends the winter hibernating in caves, or in the cellars, ice houses and underground passages of "the big house", and some of these sites have been fitted with grilles, to protect them from disturbance. There have been huge reductions in the European populations of these bats, almost to extinction in some countries so the Irish colonies are all the more precious.

Most attic-roosting bats disperse in the autumn to crevices in stone walls, or hide themselves under piles of stones to tick over for the winter.

Yes, they do leave droppings behind them - sometimes an inch or two deep, if the roost has been used for years. They're about the size of mouse droppings, consist largely of brittle (but indigestible) fragments of insect cuticle and - unlike rodent droppings - crumble easily to a fine, dry powder.

Think of them as extra insulation. Think of bats as swallows of the night. "Ah!" you will cry on a warm May evening, "the bats are back!"