After spending last week gathering post vegetation removal home range data, we are now spending three weeks monitoring the locations and mortality rates of our voles at all sites. We visit each site twice a week, making sure that we have pinpointed each vole’s location as accurately as possible and giving our best guess as to whether it is alive or not. So far this has involved more pushing through dense undergrowth to pinpoint voles who have moved to burrows underneath bramble patches, and wading out across the river to check that voles on the opposite bank are alive and well.
So far we have had relatively few casualties, although some are inevitable. Emily did come across a very neat pile of intestines and a collar at one site earlier in the week, all that was left of one unfortunate vole.
To give you a better idea of how we radio track, we have taken this video.
You can see Charlotte moving towards the suspected location of this particular vole, following the pulsing signal. Pointing the aerial at different areas of the bank allows us to get an idea of in which direction the signal is strongest. At about 10-15 seconds in, when the signal is very strong, she turns down the gain and switches to the attenuated mode, narrowing down the signal even more. You can hear the sound of the beep change and grow quieter. Finally, having followed the ever-louder signal and discovered that the water vole is in a certain clump of vegetation, she uses the aerial to determine whether it is in the water (fainter beep, not there) or underground. At the last, you can hear the beep becoming much more insistent when the aerial is perpendicular to the river about a meter from the water’s edge. The signal is strongest when the aerial is in line with the antennae on the radio collar. From this we can tell that the vole was underground (she checked the vegetation and the vole is definitely in a burrow) and facing towards or away from the riverbank.
After the video Charlotte then stood above the vole for a further 3 or 4 minutes, keeping the aerial in exactly the same place. Because the signal is strongest when the aerial is in line with the antennae on the collar, any movement by the vole is easily heard as a change in signal volume. This vole did move, so is almost certainly still alive. A quick mark on the GPS and noting down of the coordinates, and we can move on to the next vole.
We will be continuing this monitoring for the next 2 weeks, before we start to re-trap and remove collars. It will be interesting to see how vole mortality compares between sites.
Charlotte and Emily
For more information on this project or to donate to this work, visit our Appeal page or the WildCRU website. You can also keep up to date with this project on Facebook and Twitter. And for more cute pictures of water voles, visit Andrew Harrington’s website http://u0000vs933onpn8m.photoshelter.com/gallery/The-dark-water/G0000KcrP4sU1uGs/