Water Vole Survey Report

Here is a very interesting and informative report, written by mammal recorder Linda Biddle, detailing the reintroduction of water voles to Rutland, their subsequent monitoring and results. This report was published in the Leicestershire and Rutland Recorder issue 12, 2016.

Water Voles Reintroduced to Rutland

By Linda Biddle, Mammal Recorder, Rutland Natural History Society

The case for reintroduction

When, in 2011, the Leicestershire and Rutland Wildlife Trust (LRWT) was planning a water vole (Fig. 2) reintroduction programme at Rutland Water Nature Reserve (RWNR) and needed to obtain a licence, it had to provide evidence of their historical presence in the area. Water vole records made by the Rutland Natural History Society (RNHS) showed that they were quite commonly seen in the 1960s and in the area now covered by Rutland Water, but the number seen in Rutland had declined seriously between 1965 and 1976 (Fig. 1). They held on in low numbers but by 2010 were probably present at only one or two locations. They had been widely predated by American mink and impacted by poor water quality and pollution. By 2010 numbers were so low that natural regeneration was impossible, the communities being very widely separated, so that there was no chance of gene exchange between colonies which is essential for maintenance of a healthy population.

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The maturing habitat at RWNR was eminently suitable for water voles in some areas and presented an ideal opportunity for their reintroduction. If successful, this could provide a protected environment in which the species could thrive and hopefully spread outwards and recolonize waterways in the county.

Preparation

The reintroduction has to be preceded by a thorough survey of the local waterways for relict populations and confirmation that mink were not present in the area proposed for recolonization. The extensive survey was carried out by LRWT staff, investigating for field signs such as burrows, areas grazed into “lawns”, latrines and stems chewed off at 45°. No colonies were found. Mink detection rafts (Fig.3) were placed in waterways feeding into Rutland Water and at points in and around the reserve, again without positive results. The monitoring of these rafts has continued, and when mink footprints are detected, a trapping regime is followed to ensure that the reserve remains free from mink.

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Reintroduction 2011-2012

The licence having been granted, Derek Gow and Associates was approached for stocks of captive bred water voles and in May 2011 the first tranche of animals was released in one location at RWNR (Fig. 6). Further reintroductions took place in September 2011 at locations at Egleton and the north arm of the reserve with more in May and September of 2012. A single release took place in September 2013 on the south shore of the south arm at Waderscrape hide (the osprey observation site). At each of the two sections of Oakham canal still remaining, north of the town and nature reserve, a single release took place in 2013. Some releases were simple one stage or “hard” release, others were “soft” release, that is the voles retained in cages in the release site for several days, fed daily on carrots and apple, then a baffle was placed across the front of the cage so that the voles could come and go while food was still available. Eventually after around ten days the cages were removed.

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Monitoring and recording

Water voles mark their territories with latrines formed from piles of droppings (Fig. 5). Females normally defend territories of around 30-150m and males 60-300m. They will mark natural features such as a flat patch of bank or a tree stump with more droppings being found when voles are more active. In October 2011 small water vole monitoring rafts were placed at 10m intervals along the ditches and streams of the release sites, usually around ten per site, on longer stretches as many as 25. These were monitored weekly throughout the winter. At each visit, water vole droppings were counted then swept off. The voles also make food piles and on occasion use the rafts for constructing a “salad” of neatly arranged short sections of reed stems or other vegetation.

The recording continued to cover the wider distribution of releases until 2014 when fewer rafts per site were deployed. The number of rafts was reduced to five per 20m per site and the visits reduced to fortnightly and then monthly although the interval between cleaning the rafts and revisiting to count remained the same. In 2015 the number of visits was reduced to three per season, spring, summer and autumn. Investigation work was also carried out in 2015 with Nottingham Trent University to evaluate the effectiveness of assessing populations using five rafts set at 20m intervals on four consecutive days which will continue in 2016.

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Results

Some sites, apparently ideal for water voles, were not successful as homes for permanent colonization. Any site with low overhanging trees, or shallow slopes to the banks soon had much reduced or no signs of territorial marking. The shallow banks at Burley fishponds under willow trees, where reintroductions has taken place in 2011, were devoid of water voles by January 2012. Similarly along a channel overhung by trees at Smew hide, the rafts were empty from January onwards. Later reintroductions, along the foreshore by Osprey hide, remained populated during the summer when vegetation covered the edge of the water. In winter when vegetation had died down revealing the shallow sloping shore, the voles disappeared. Further into Burley fishponds, where a channel runs around the edge of the reedbed, later reintroductions and monitoring showed that a healthy population had become established.

A pattern of reduced activity in the early months of the year, the a gradual increase as the year progresses, to a peak in September and October (Fig. 7) reflects food availability as vegetation dies down in the winter. When vegetation regenerates to a sufficiently high level breeding takes place and signs of activity increase and, eventually, the offspring spread out and colonize along the streams and channels at the perimeter of the territory.

2013-graph-from-report 2014-graph-from-report

Along reedy channels in meadows with a constant water level the voles did very well and reedbed sites also showed steady activity levels. At Dog Kennel stream there is a steep bank, and after heavy rain the stream soon becomes a torrent, depth rapidly increasing. This often washed the rafts onto the banks, or scoured the droppings off the rafts, so results here were variable. However, when rainfall was low or steady the lower section of the stream showed positive signs of presence of voles, showing their ability to cope with the changing water levels as long as other factors remain favourable.

The most constant population was at Wet Meadow on Lagoon 1, a reedy ditch around the edge of the meadow. This was the first release location and remains a well populated site today. An adjacent channel in front of Snipe hide, which was clear of vegetation in 2011 and 2012, did not attract water voles for some time, but as reeds and other vegetation have colonized it has become a very active site, even in winter. At Shoveler hide on Lagoon 3 a channel with reedy vegetation had also been a very successful location, but in the winter of 2013/14 it was cleared of vegetation with the resulting loss of habitat and the population disappeared. This channel is connected at one end to a large reedbed and, again as the vegetation reappeared, the activity of water voles has recovered so that by the end of 2015 levels were similar to those found earlier. The reedbeds appear to act as a safe haven for the voles, a reservoir for recolonization, as long as predation is prevented.

A colony on Heron Bay on the south arm of RW and another at two small ponds nearby have maintained levels of activity. At Waderscrape hide on the south shore where a small reedbed sits in front of the osprey observation hide, there is a very active population, entertaining osprey watchers in quiet moments by paddling across each of the three small channels in front of the hide. At Oakham canal the reintroduction also appeared to have been successful with good active signs detected until April 2015 when there was a drop in activity. A few signs were found for the rest of the year. In January 2016 no signs were found; it is hoped that activity will increase as the season continues and that the population has not been lost.

The project appears to have been very successful in that a healthy population of water voles is now established at a number of sites at RWNR. These populations seem able to recover when reduced as long as they are able to connect with neighbouring colonies. The populations on RWNR and nearby will continue to be monitored while also maintaining vigilence for the presence of mink using the rafts. It remains to investigate the streams around the reserve to find out if colonization further afield has taken place. This was always an important aim of the project and it is hoped that this spread will take place if it has not already done so. Landowners around the area have been encouraged to deploy the mink rafts and to reduce the presence of mink in the locality.

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Acknowledgements

Thanks are due to the small band of willing helpers who braved all weather conditions to assist in collecting information over the last four years (several of whom had unexpected and unwelcome experiences of water vole habitat at closer quarters than they would have liked!), LRWT water vole reintroduction project staff, Anthony Biddle, Peter and Judith Harrison, Anya Wicikowski, Peter Scott, RNHS records and Anglian Water for funding the project.

Reference

Gow, D. 2007. Water vole reintroduction projects, the lessons and success factors. ECOS: 28(1).