Spring 2007 issue

Simply Bats

Bats, the only mammals capable of true flight, account for a fifth of mammalian species. They are more closely related to humans than to mice and can live over 30 years, but breed slowly: a mother bat usually has just one baby a year. There are 17 species in Britain. Several are rare, and one almost extinct. To stem the steep decline in our bat population, all bats and their roosts are protected by law.

British bats feed on insects. They find their meals on the wing using echolocation, which enables us to detect and identify them using simple bat detection equipment. Around Thames Ditton and Weston Green we have at least eight species including Daubenton's 'water' bats, less common ones such as Noctules, and the Serotine, a larger bat found in the South-East which is fast declining and the subject of a Species Action Plan in Surrey. Ross Baker and Lynn Whitfield who run the Surrey Bat Group and until recently lived in Weston Green, write: "We have very few roost records for Thames Ditton and would welcome more reporting. The playing fields around Weston Green often have Noctules and Serotines feeding over them on the insects attracted by floodlights. Pipistrelles of both common species are abundant. We would also expect brown long-eared bats to be in the woodland areas, but these bats are difficult to pick up on bat detectors because they whisper their echo-location calls. We need firm evidence of roosts, such as bats observed entering buildings or tree-holes, or crumbly mouse-like droppings in the loft."

Bat boxes can be installed to attract bats to your garden. Bats move roosts at various time of the year according to whether they are hibernating, breeding or in transition. Collectively, the three species of smaller Pipistrelles have broad tastes and will happily roost in trees and modern buildings, whereas Serotines seem to prefer older Victorian and Edwardian houses with slate roofs and gable ends.

The Thames is good for Daubenton's bats, which require low light levels. Bats are not blind. While some bat species feed on insects attracted to lit areas, all are themselves highly sensitive to light levels and increasing light pollution can be a serious matter. To research this problem, local ecologist Alison Fure organised a survey by boat along the Thames from Teddington to Hampton Court last year, accompanied by some forty interested representatives of English Nature, Thames Landscape Strategy, assorted Councils and other groups concerned with river management. She plotted light levels, GPS position and signals received from 406 bat flights, demonstrating that as light levels increased bat activity decreased directly.Where there was no background light spillage there was greater diversity of species. Daubenton's bats, in particular, were not found above 1.0 lux, whereas lights on Hampton Court Bridge emitted 19 lux and Kingston Bridge a whopping 31 lux where no bats were present. Garden security and decorative lights can also be a problem for bats.

We're lucky to have in our area one of the most important havens for bats at Seething Wells, where there's a substantial labyrinth of underground tunnels and structures, some of which are statutorily listed. These are used by eight species, and include a roost where mothers of the Daubenton's bat congregate to give birth and rear their babies. Natterer's bats are recorded here even during the winter and use the complex structures for hibernation. Noctules feed over the filter beds; Serotines are seen occasionally while the three Pipistrelle species are frequently recorded. There are brown long eared bats along Barge Walk. Seething Wells is now a designated site for its wildlife value, and so important for our less common species, particularly the light-sensitive Daubenton's and Natterer's bats, that it's essential to prevent any further increase in light pollution and to forestall plans for development that would increase light levels or otherwise disturb the habitat here.

If you'd like to play a part in securing the future of Seething Wells as a designated wildlife site, you can join the fledgling Friends of Seething Wells - details from Alison (below). You might also like to acquire an inexpensive bat detector and some training from the Surrey Bat Group in its use. Bats hibernate over winter, so you won't get cold, and it can be pleasant monitoring them of a summer's evening when they awaken and come out to feed some half an hour after sunset. The Surrey Bat Group would like to hear from you - and if you do this, please let us know - we'd like a Village Bat Correspondent!

We owe the preparation for this article to:

Alison Fure, Furesfen Ecological Consultancy, 28 Bonner Hill Rd, Kingston upon Thames KT1 3HE tel: 0208 974 6670 email: alison.fure@blueyonder.co.uk

If enough people are interested, Alison will organise a 'batty' boat trip along our stretch of the Thames this summer. This would take place at and after sunset, on a large boat with wine, bat detectors and experts. Children get very excited when they see the larger bats! Let her know if you might want to join this cruise.

Ross Baker and Lynn Whitfield, Surrey Bat Group email: bats@rosslynn.wanadoo.co.uk

Links:

Bats and Planning considerations

Bat Conservation Trust

Commercial bat detectors