Pipistrelle: Pipistrellus pipistrellus & P. pygmaeus
The pipistrelles are Britain's smallest bats. They vary in colour, but are usually medium to dark brown on the back and only slightly paler underneath. They are the most common species in towns. Only very recently have scientists recognised that two separate species have been confused under the name P. pipistrellus. Their flight appears fast and jerky as they dodge about pursuing small insects, which are caught and eaten in flight. A single pipistrelle may consume up to 3000 insects in a night.
Bat Facts
|
Description | |||
| Head and body length |
35 - 45mm | ||
| Forearm length | 28 -35mm | ||
| Wingspan |
190 - 250mm | ||
| Weight |
3 - 8g | ||
| Colour |
Medium to dark brown | ||
|
Life cycle | |||
| Mating period | Autumn | ||
| Maternity colonies | Established late spring. Young: one (occasionally twins) born early June to mid - July, weaned at six weeks | ||
|
Colony size |
25 - lower 100s (up to 1000+) | ||
|
Longevity |
Up to 16 years | ||
|
Habitat and food | |||
|
Summer roosts |
Buildings & trees | ||
| Winter roosts | Buildings | ||
| Feeding habitat | Over water, marshes, in open woodland, woodland edge, farmland, along hedgerows, suburban gardens and urban areas | ||
|
Food | |||
| Mosquitos |
Midges |
Small moths | Lacewings |
The two species were originally identified by differences in their echolocation calls, with the difference confirmed by DNA studies. Scientists are now busy working to identify differences in the ecology and behaviour of the two species.
As with all British bats, the echolocation sounds used to detect their prey are normally inaudible to humans, but some people can detect the lower frequency parts of these high pitched squeaks.
Breeding
Mating occurs during autumn at well established mating roosts and occasionally in spring. Maternity colonies consist almost exclusively of female bats. Maternity roosts are occupied between May and August and sometimes into September. Females give birth to their single young (occasionally twins, particularly in Scotland) from early June to mid-July, though births as late as August have been recorded. The young are fed solely on their mother's milk. Females with young to suckle may make several feeding trips during the night, while the young are left inside the roost in a group or creche.
Within three weeks the young make their first flights and by six weeks can forage for themselves. Most colonies start to disperse soon after the young are weaned.
Pipistrelles may remain at a single site during this time, but more often, particularly in newer housing, they move irregularly between several sites within a small area. As a consequence numbers at any one site can fluctuate markedly through the summer.
Females can reach maturity in their first autumn, but most males will not reach sexual maturity until the following summer.
Summer roosts
Buildings are the most favoured roost sites and more than half of known roosts are in buildings less than 30 years old. Pipistrelles prefer to roost in very confined spaces around the outside of the building, typical sites being behind hanging tiles, weather boarding, soffit and barge or eaves boarding, between roofing felt and roof tiles or in cavity walls. Pipistrelles rarely enter roof spaces except in the more stable, well established large colonies found particularly in older buildings.
There may be a slight smudge around a well-used access hole, otherwise the only evidence of bats is the presence of droppings beneath the favoured entrance, on windows, window-sills and walls. Pipistrelles are also found roosting in treeholes and crevices, behind ivy and in bat boxes. The access hole can be a slit as little as half an inch wide.
Pipistrelles can be active within the roost during the day especially if young are present and the roost gets very hot. They may also be noisy as the time for emergence approaches. They usually start to emerge from the roost about 20 minutes after sunset. Large numbers of pipistrelles circling around the roost entrance at dawn make a spectacular sight.
Winter roosts
Despite being by far the most frequently recorded species in summer, few pipistrelles are found in winter. Most winter records are of isolated individuals or small groups in crevices in buildings and trees so their presence often goes undetected. They often roost in fairly exposed situations to take advantage of warmer weather to feed. They are only very rarely found roosting in caves or tunnels.
Extreme cold weather forces them to change roost and at such times they often appear in houses - and individuals in poor condition are found in unlikely places, such as hanging in the open on a bare exposed wall.
Ultra-sound
The calls range from 40 - 80 kHz. With a bat detector the clicks turn into "slaps" towards the bottom of the frequency range. The two species are separable with a bat detector: in one the peak frequency is at about 45 kHz, while it is at about 55 kHz in the other species. However, their "social" calls are emitted at between 20 - 30 kHz and are heard as a "chonk"; this is audible to some adults and children.
Status and distribution
The pipistrelles are Britain's most common bat species and are found throughout the UK including the Isle of Man. They are also abundant and widespread in the rest of Europe.
Conservation
Pipistrelle bats have probably declined as a result of modern agricultural practices. Their reliance on buildings makes them vulnerable to renovation work, exclusion and toxic remedial timber treatment chemicals.
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