Field voles reach plague levels in Scotland
After posting my photo of an outrageously cute field vole last week I did a little digging and found an interesting story on the BBC from earlier this year.
It turns out field voles have had an exceptional couple of years because of the long-lasting snow cover, and are now reaching what would normally be called ‘plague’ conditions.
When a snowpack forms it benefits small mammals in two ways. It insulates them against the worst of the weather, maintaining a constant temperature of 2-3C and avoiding those penetrating sub-zero temperatures above the snowpack. It also offers protection from predators, with the usual suspects such as kestrels, buzzards and owls left wondering where all the food has gone. When the snow melts, a network of runs and tunnels are revealed in the flattened grass.
Come Spring when the voles are breeding, the population is swelled to enormous proportions by the sheer numbers that survived the winter and became parents. Aberdeen University professor of ecology Xavier Lambin said it was very difficult to work out the total number of field voles in Scotland, but that it could be in the region of 60 million. This year however, the figure is potentially 10 times that, pushing their number into the hundreds of millions.
And then of course the predators have a field day (no pun intended) once the snow has gone, with easy pickings from the masses of voles scurrying along the ground. The British Trust for Ornithology has reported that raptors and owls are thriving this year and are having large broods. Especially the short-eared owl.
Certainly this rings true in Fife, where we had lying snow for 50 consecutive days. When the snow melted in January, the network of runs through the grass was conspicuous and extensive…..though I never actually saw a vole. As indicated by the BTO there have been plenty of kestrels and buzzards overhead in Fife, and I’ve been chuffed to see my first ever short-eared owls up here too, which perhaps is an indication of how many voles have survived this year.
In 2007, Spain got special permission from the European Union to undertake controlled burning of 400,000 ha of farmland after field voles reached plague levels and threatened the beet and potato crops. If we get another winter like last year, one wonders how big our population can get and what impact it will have on our farmland.
Photograph: Durlston Country Park (via Flickr)
I’ve been watching raptor cams based in Estonia. My understanding is that the voles have a three year cycle and this is a high year for them — good snow cover probably exacerbated the normal fluctuations. Last year most of the owl chicks starved to death, because it was a low vole year — of course the resulting reduced number of predators helped to make this a big year for voles.
But then the Lesser Spotted Eagle chick was very well fed this season — early on frogs and then as things dried up cute little vole after cute little vole. On many days as many or more than 5 or 6 voles were delivered.