Today’s guest blog comes courtesy of Robyn Stewart, Glasgow’s Water Vole Ambassador. The discovery of thriving populations of water voles in a residential area of Glasgow away from traditional habitat is considered to be of national significance. SNH are supporting Glasgow City Council and the University of Glasgow, who are working in the local community, to help conserve this unique population, and Robyn leads that work.
Water voles need water right? Surely the clue is in their name….but if I were to tell you that there is a thriving population alongside the M8, Scotland’s busiest motorway, you could be forgiven for doubting my wildlife identification skills.
The east end of Glasgow is a far cry from the pristine image of wetland habitat we associate with water voles yet remarkably high densities are being found here several kilometres away from water in grassland habitat such as road verges, brownfield sites, and even the occasional back garden.
Water voles have long been associated with water and their distribution is usually considered to be limited to the distribution of wetland habitat. Their movements are often quoted as rarely exceeding two meters beyond the riverbank and they are also notoriously fussy: they like dense vegetation which they both eat and hide in, soft banks to burrow into and the flow of the water must be not too slow but not too fast either.
While their habitat preferences have been relatively well researched it is surprisingly little known that European populations of the water vole, from which our water voles originated when they colonised the UK during the last Ice Age, have long been known to be capable of living in non-aquatic habitats. These non-aquatic voles are normally found in grassland habitats and this behaviour is termed fossorial in reference to their predominately subterranean existence.
In fact, the grassland populations found in some upland areas in mainland Europe can peak at 1000 water vole per hectare, a truly mindboggling image given as even a fraction of these numbers is unheard of in the UK. In contrast, most of our water vole colonies are spread linearly along a water course and even reed bed populations only reach a maximum of 40-50 animals per hectare.
In addition to this, water vole populations have also undergone one of the fastest declines of all our native mammal species in recent years, dropping 88% UK-wide and up to 98% at a local scale in some areas.
Their decline started in the 1900’s as land use changed considerably resulting in the loss of wetland margins with the move towards intensive agricultural and the overall UK trend towards urbanisation. However, the catastrophic decline that we see nowadays started in the 1950’s with the accidental introduction of the non-native, semi-aquatic American mink: water voles have no way to evade these efficient hunters with mink being small enough to enter the burrows that water voles dig in order to have a safe place to hide from predators.
As American mink spread from one water course to another, a crash in water vole numbers would soon follow. Water vole populations simply could not recover from the combined effects of heavy predation on top of widespread habitat loss and fragmentation. As a result, water voles are now protected in the UK and a priority biodiversity species for many local authorities and wildlife conservation organisations.
So when the east end water voles came to light back in 2008 after a single animal was accidentally caught in a rat trap set in a housing estate in the east end, Glasgow City Council reacted quickly. Surveys revealed extensive water vole field signs, such as burrows and feeding remains, in grasslands throughout the area which prompted the Council to fund a research project alongside the University of Glasgow to map the distribution of the fossorial animals and investigate their habitat preferences.
It also couldn’t be more timely given the initial surveys revealed thriving water vole populations were located on the exact brownfield sites being targeted in the much needed regeneration plan of Glasgow’s east end by the Scottish Government and Glasgow City Council.
So what did the study reveal? Firstly, two distinct types of water vole exist in Glasgow with the habitat mosaic of east end providing habitat for both the fossorial water vole as well as the more familiar wetland type. Multiple fossorial breeding colonies were found throughout the east end and some were over 1800m from the nearest wetland habitat. Secondly, the distribution of fossorial populations was strongly linked to the M8 corridor and surrounding grassland patches in an almost linear fashion.
Surprisingly, despite the huge amount of disturbance from the motorway traffic, the long grasses which characterise the motorway verge provide the water voles with a continuous swath of grassland habitat in which they can move freely without breaks or barriers, something of a rarity in the environment these days. The fossorial water voles actually preferred habitats which were in close proximity to people because human presence created the road verges, parks and gardens which provided soft banks to burrow into and dense grassland swards full of palatable, disturbance-tolerant grasses like Yorkshire fog and Bent grasses. Even though it was completely by accident, urbanisation in this particular instance was an actual benefit to wildlife.
I am often asked what caused the east end water vole populations to move into grasslands but to be honest it is still somewhat of a mystery and difficult to ascertain without genetic analysis. It is possible that populations here are a relic of those once found along the Monkland Canal prior to it being filled in for the creation of the M8 which may in turn have forced the water voles into surrounding grasslands.
Regardless of the origin of this behaviour, it gives the water voles one huge advantage: grasslands act as a refuge from the American mink because they are so far from the mink’s normal wetland hunting grounds. There was no evidence that moving into grasslands was a behavioural adaptation to avoid mink however, as there are no records that American mink and water vole were found in the same area.
Indeed, evidence from this study lends more weight to the theory that moving into grasslands is the expression of an ancestral behaviour from their founding European colonisers. The fossorial water vole may be far more common than we realise because current survey guidelines are limited to wetland habitats. Records of fossorial behaviour in the UK do exist, dating back to the 1900s and studies at the University of Aberdeen revealed extensive populations in grasslands on small islands in the Sound of Jura.
Off the back of the University of Glasgow study has come some fascinating ground-penetrating radar research mapping the subterranean burrow system of the fossorial water vole with geophysicist experts at RSK. Preliminary findings have shown that the burrow system varies considerably from the normal wetland water vole arrangement, with an outer ring of burrows connected to the central nest chamber in a pattern also linking up food stores and bolt holes.
The area occupied by a fossorial water vole territory also appears to be much smaller, an area of 8 x 10m, compared to the 30-150m length of river margin required by the wetland type.
These findings, along with the main study, are going to inform habitat management and creation guidelines for Glasgow City Council as they face the difficult task of balancing the protection of these incredible fossorial populations alongside the regeneration of the east end. The Council are being hugely proactive though and incorporating water vole distribution into their city masterplan which will go to inform future development decisions.
All in all, the east end water voles are a beacon of hope for the future preservation of water voles as grasslands tend to be a product of urbanisation rather than one under threat from it, and are also comparatively cheap to produce and manage, and crucially mink-free.
Photos, unless otherwise stated, courtesy of Robyn Stewart.