Explosion of common vole population in Castilla

The explosion of the population of Common vole (microtus arvalis, topillo campesino), estimated at some 500 million individuals, in Castilla-Leon this year has devastated some 400,000 ha of crops. The origins of the population boom are in this year’s mild winter temperature, the cyclical nature of vole populations, and in the long term in its move into the cereal plains where now “there are few natural predators.” Until 20 years ago, the common vole was only found at medium and high altitude meadows in the Pyrenees, Picos de Europa and the Sistema Central. Juan José Luque from the Universidad de Valladolid notes here «We are not entirely sure why, but we can say that the agricultural changes in the cereal steppes from dry farming to irrigated crops has helped their expansion”

Vole pests Collecting voles in Valladolid

Experts from the Ministry of Agriculture and environmental groups recommend the use of predators, parasites and natural pathogens, but farmers are up in arms demanding and indeed using toxic chemicals, with all the consequent dangers for humans and wildlife (see below). Similar vole explosions occurred in 1988-89 and 1993-94, which then subsided due to natural causes. More here from Consumer

Photo of a common vole

Read Dave’s post on Castilian voles on the Forum. This is first hand experience on the ground and is frankly more interesting than my above piece” This year has been a very mild year in Castilla and Leon, and so the common or garden field vole, has survived in large numbers, something that occurs fairly often, in a similar way to Lemmings. The area south of Leon is called the Tierras de Campo, and covers the provinces of Palencia, Leon Vallodolid and Zamora, and it is called the breadbasket of Spain for obvious reasons, for this is Cereal country. Voles like the young shoots of Cereal crops, and were posing a significant threat to this years crop, and the farmers were worried, and approached the Junta of Castilla and Leon for a solution to the problem, threatening street protest if no action was taken. Continue reading

Wikipedia notes “The population density of Common Vole, Microtus arvalis varies seasonally and exhibits a considerable long-term fluctuation that shows typically three-year or five-year cycles. Densities can range from 100 individuals per ha (very low level) over 500 individuals per ha (medium level) up to 2000 individuals per ha in some years.