July 2004: Wildlife Survey

In July Clare Cadman from the Essex Biodiversity Group kindly gave up her evening to lead the Landscape History Group in a survey of the Castle area, so that we can be aware of its wildlife value and ensure that our project does not disturb things. She brought with her all the equipment and reference cards and books for identifying what we found. First Clare talked about wildlife and surveys in general. The main protected species are bats, badgers, reptiles, great crested newt and dormice. You search for adult newts between March and May. As well as their roosts being protected, the feeding areas and travel routes of bats are protected. Bats will only fly along lines such as hedges, walls etc. A gap of only 20m is enough to make bats turn around and go back. Next we got some water from the moat to look for water life. The water was teaming with water fleas. In addition we also identified:

- Adult Diving Beetle and larvae

- Mosquito larvae

- A Newtlet (Either Palmate or Smooth)

Then we went into the Dam Meadow to look for field life. We used nets to "sweep" the grass and specimen pots to put anything interesting in for identification. In about 5-10 minutes we collected the following:

- Roesels Cricket

- Bush Cricket

- Common Green Grasshopper

 - Ladybirds

- A moth caterpillar

- Crab Spiders

- Green and Hawthorn Shield Bugs

- Garden Hover Flies

- Soldier Beetles

- Ants

- Wolf Spider

Clare told us that areas of grass which are left un-mown are best for wildlife. If a strip a meter wide can be left along a fence or hedge line that that makes a big difference, even if a whole field can't be left.  We finished off the evening by looking for bats in the meadow and the churchyard. Clare gave us each a bat detector. These have a volume control and a frequency control. Different bats use different frequencies for echo location. There are 980 bat species in the world of which 16 can be found in the UK and 10 in Essex. The population of Pipistrelles, which are the UK's most common bat, fell 28% between 1970 and 1993. This is mainly due to loss of habitat. There are believed to be three main reasons why bats come out in the evening: there is lots of food about (flies and moths); fewer predators; fewer other creatures eating the food. Bats mate in September but do not become pregnant until the following year.  Between May and June the females build their roosts and give birth during June and July. There are three types of Pipistrelles. They are called the 35, the 45 and the 55 after the frequency with which they do their echo location. We tuned our detectors to roughly 45kHz. As bats passed us by we heard their sonar and tuned our detectors in to get the best sound. When the bats are flying along looking for something the sounds are in short bursts with a significant gap. As the bats get closer to their prey the period between bursts becomes much shorter until the final few moments when it is more like a buzz. This is known as the Death Buzz.

Helen Bryant