We met at Teddington Gate at 8:30pm. As bats don't leave their roosts until sunset, Nigel had a few minutes to introduce his walk with a few facts about Bushy Park itself.

It is 445 hectares or 1099 acres and is the second largest of the Royal Parks. It's an important area of acid grassland with many important plants including Mudwort, the only site in the London area. For its value to a wide range of invertebrates the park satisfies the criteria for designation as a SSSI (a Site of Special Scientific Interest) and The Royal Parks are working with Natural England to further the possibility of designation in the near future. The Longford River which runs through the park and feeds all the ponds has two Red Data Book species - a mayfly and a beetle. There are 123 nationally scarce or threatened species recorded in the Park so far.

Six species of bats were found in the park in a survey carried out in 2004 by sound alone - although there are probably ten species altogether. The UK has 16 or 17. The Common Pipistrelle (pictured right, top) is relatively tolerant of lights and will live under roof tiles. The Soprano Pipistrelle (pictured right, second top) is also here, and no prizes for guessing it has a higher frequency that the common one. Daubenton's bat (pictured right, third top)can be heard over water not catching fish, but low flying insects.

There are Serotine bats (pictured right, fourth top) and occasionally Long-eared bats (pictured right, third bottom)- which use a very quiet echolocation call and both listen and look (with their relatively large eyes) for insects which they glean from vegetation. Bats are not blind but have quite good eyesight although, like many mammals, only see in black and white. They use echolocation for navigation and finding insects by emitting high frequency calls of 20kHz or more (ultrasound) and listening for the echoes reflecting off objects and prey around them. Children can usually hear high frequencies (over 20kHz) but as they grow older lose that ability, so it was just as well that Nigel brought along some bat detectors. Having gathered close to where Nigel knew there was a roost, we heard many Common Pipistrelle bats echolocating at around 45kHz as they left for their nightly feed.

Dusk is a busy time for bats as they are hungry after spending the day in the roost. Answering a question about why bats feed at night, Nigel explained that there was too much competition from insect feeding birds during the day; there are too many predators about and many insects become active as dusk falls. Barn owls are known to predate bats, but sadly Bushy Park doesn't have any of those.

The numbers of bats have declined dramatically in the last 60 years or so, mainly because of large scale reduction in the quality of habitat in the countryside generally; also our buildings have fewer crevices for roosting; and cavities in trees suitable for roosting are often removed as part of works to make trees safe for the public. Some parts of the park are closed to the public so that standing trees can be left to rot and wildlife can flourish with no interference from humans.

We heard several species of bats and even though light rain began to fall, the bats were still active. As well as the Pipistrelles, we heard the dry clicking calls of Daubenton's bats foraging over Heron Pond. Bats have to make use of all available feeding time and only in very heavy rain will they return to shelter.

It was a fascinating walk and talk by Nigel. He said at the start that he wasn't a specialist, but he could have fooled all of us. He gave us a remarkable insight into the world of bats, and I'm sure the sale of bat detectors will be increased by all us new converts.
Pieter Morpurgo, June 2008

Also pictured: Natterer's Bat (right, second bottom) and Noctule (right, bottom).

Links:
www.bats.org.uk - Bat Conservation Trust
www.royalparks.gov.uk - Royal Parks