Noctule bat: Nyctalus noctula
The noctule bat is one of the largest British species and is usually the first bat to appear in the evening, sometimes even before sunset. Adults generally have short, sleek, golden evenly-coloured fur. Juveniles, newly moulted adults and some females are a dull chocolate brown colour. They have broad brown ears and a distinctive mushroom shaped tragus.
Noctule bat Facts
| Description | |||
|---|---|---|---|
| Head and body length | 60 - 82mm | ||
| Forearm length | 48 -58mm | ||
| Wingspan | 320 - 400mm | ||
| Weight | 18 - 40g | ||
| Colour | Adults golden brown, juveniles and some females dull chocolate brown | ||
| Life cycle | |||
| Mating period | August to October | ||
| Maternity colonies | Late spring. Young: usually one, born late June or July and weaned within six weeks | ||
| Colony size | 15 - 50 bats (occasionally 100+) | ||
| Longevity | Up to 12 years | ||
| Habitat and food | |||
| Summer roosts | Tree dwellers, occupy woodpecker holes and rot holes. Seldom in buildings | ||
| Winter roosts | Trees, rock fissures and hollows, bat boxes, buildings | ||
| Feeding habitat | Over deciduous woodland, parkland, pasture, water and at forest edge | ||
| Typical food | |||
| Moths | Cockchafer beetles | Dung beetles | Flying ants |
Noctules have a characteristic powerful, direct flight on narrow pointed wings. They fly in the open, often well above tree top level, with repeated steep dives when chasing insects. Noctules can fly at 50kph (30mph).
Most food is caught on the wing and eaten in flight, but occasionally prey is taken from the ground and in suburban areas noctules are attracted to street lamps to feed on moths. During spring noctules will feed mainly on smaller insects such as midges, changing their diet to take beetles and moths later in the season. They forage mainly at dusk for up to two hours and for about half an hour at dawn.
Breeding
During the summer male noctules are solitary or form small bachelor groups. A single male establishes a mating roost during late summer, usually in a tree hole, for several weeks and defends his roost against other sexually mature males. He emits a series of shrill mating calls from the roost entrance or during flight and produced a strong odour, attracting a harem of four or five (up to 20) females, which stay with the male for one or two days.
In April noctule bats begin to form mixed sex colonies and can be found in tree holes, buildings and bat boxes. Such colonies often break up in late spring and smaller maternity colonies are found in tees, rarely in buildings and bridges. The young are born in late June or July. Females usually have one young, but twins are regularly recorded. For three to four weeks the young are suckled solely on their mothers milk, and are fully weaned and able to forage for themselves within six weeks.
The maternity colonies frequently change roosts, mothers carrying the smaller young between roosts during lactation. The young are left in crèches while the mothers go off to feed.
Some females become sexually mature in their first autumn, but many do not mate until their second year. Males participate in mating from the end of their first year.
Summer roosts
Noctule bats are primarily tree dwellers and live mainly in rot holes and woodpecker holes. They occur rarely in buildings, but will use a wide variety including modern houses. Within buildings they roost in gaps in large ridge tiles, behind hanging tiles, between the ceiling and floor boarding, above large soffits, between the tiles and ceiling of a converted attic. Sometimes they roost in the lining of tall disused industrial chimneys and other hollow walls including cavities in bridges.
Most noctule roosts in buildings are only gathering roosts, the colonies moving of at the end of May and early June. The bats produce loud characteristic metallic chirping sounds so that noctule colonies can be heard up to 200-300 meters away on hot days.
Winter roosts
Noctule bats hibernate mainly in trees or rock fissures and hollows, but have also been found in bat boxes, buildings and other man-made structures in winter. The sometimes form large mixed-sex winter aggregations of up to 1000 on mainland Europe, but the group sizes are smaller in the UK.
Noctules have been observed feeding at any time of winter if conditions are suitable, but most can survive successfully without feeding for nearly four months and can tolerate external temperatures as low as -16° Centigrade.
Ultra-sound
Noctule ultra-sound can be heard by some adults and children. The calls range from 20-45kHz and peak at 25kHz. On a bat detector a characteristic "chip-chop" with occasional clicks can be hard when feeding.
Status and distribution
In continental Europe the noctule is a well known migrant, but apart from a few found on Orkney, Shetland and on North Sea oil rigs (well outside the normal range), such movements have not been recorded in Britain. It is still a relatively common species in much of England, Wales and south-west Scotland, but has become scarce in some areas of intensive agriculture. The noctule is absent from Ireland. It is common throughout much of Europe, but scarce in the south-west (southern France, Iberia).
Conservation
The noctule bats has declined in Britain, due to modern agricultural practices resulting in the loss of suitable feeding habitats (such as permanent pasture and woodland edge / hedgerows rich in invertebrate fauna). The heavy management and loss of suitable trees for roosting may also have contributed to the decline.
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