Back to the Newsletter Contents and Home page

Mammal Surveys in Ryedale

by Michael Thompson

Besides Gordon Woodroffe’s long-standing otter and water vole surveys in Ryedale other members of our Society have helped, and are helping at present, in surveys of British mammals for national organisations. In 1997 the second national Brown Hare survey was launched by Bristol University and funded by the People’s trust for Endangered Species: and the Bat Conservation Trust organised the first national survey of Daubenton’s.

In the Hare survey the observer is asked to walk around the periphery of a randomly-allocated 1 kilometre square and see how many Brown Hares he or she could count. The line of walk acts as a transect which may not, of course, be abolutely straight because of obstacles. Instructions are given on estimating the distance of the hare from the transect, as well as how to colour in the 1:25,000 scale maps provided to show the habitats of the surveyed area. These coloured maps, to which the line of the transects has been added, are returned to Bristol University at the end of the survey. In all it is hoped that over 700 squares will be surveyed thoughout Britain. I was allocated a square north of Hovingham, and one south of Butterwick.

The first Hare survey in 1991-92 showed that the Brown Hare population had fallen to just over 800,000 from an estimated 4 million a hundred years ago. Hence the need to monitor this lagomorph on a regular basis and to give it some sort of protection if it is to recover its numbers. [Preliminary results from the second survey suggest a total of 820,000 – pleasing in that it confirms the accuracy of the first survey, but less so in that it suggests that the population is not growing.]

Whereas the pipistrelle bat has been monitored and counted on a regular basis for a number of years no count has been carried out on Daubenton’s bat. It is thought that Daubenton’s bat is the second most common species of bat after the pipistrelle, but no one is quite certain. So if it is alsoin decline, as is suspected, then regular monitoring and counting is important. The Bat Conservation Trust organised a national survey in which over 250 sites were observed. The hope is that some 400 sites will be surveyed in 1997 and 1998, so nationally we are a little ahead of schedule already.

I was allocated a stretch of the River Rye near East Ness. (Daubenton’s bat is often called the water bat, from its habit of hunting over lakes and rivers). Using my Bat Box III bat detector I had to record the number of Daubenton bat echo-location sounds, along with their feeding zipps, every 100 metres for 1000 metres. I went to the ten stations on two occasions at dusk, each visit being separated by 14 days. I found that Daubenton’s bat was well-established in the area and I got a good set of results which I have submitted for analysis, and I await the outcome of this survey with considerable interest.

Back to the Newsletter Contents and Home page

© Ryedale Natural History Society 1999.
Page last modified 14th April 1999. Site maintained by APL-385