Josephine Pemberton, from the Soay Sheep Project, contributes this weeks diary entry:
The Soay sheep project is on the island just now. On this, our summer expedition, we have three main objectives: first, to catch the Soay sheep in Village Bay in order to assess their condition. Second, to study the plant communities in order to understand the relationship between the sheep population and its food supply. Third, to count how many sheep there are on Hirta as a whole.
To catch the sheep, we enclose them within the Head Dyke (reinforced by temporary netting where necessary) and then coax them into small netted or walled enclosuresfrom which they can be handled. We then weigh each sheep, measure its legs and horns, check its teeth, assess it for parasites and then release it. We tag any lambs without tags and then watch them over the next few days to identify the mother. We also take a sample for DNA profiling to establish who the father of each lamb is.
We measure the amount of vegetation by assessing the height of the grass, assessing how tussocky it is (more tussocks occur when there are fewer sheep), by assessing how many flowers there are, and by sorting clipped samples into species, then drying and weighing samples. Each measurement is repeated 60 times over the different plant communities of Village Bay.
To count the number of sheep on the island as a whole, three groups of observers set out from a single point at the top of the island and follow carefully designed routes established in the 1950s; these days we use walky-talky radios to avoid double counting of animals, as might occur when sheep cross the burn into Gleann Mor.
We have recently published a book about our study ' Soay Sheep. Dynamics and Selection in an Island Population'. Edited by Tim Clutton-Brock and Josephine Pemberton, published by Cambridge University Press.
AR097, a two-year old ram that lives on the west side of Village Bay, pictured towards St Brianan's, with Dun in the background