Research in five degraded landscapes in the National Park of Sierra Nevada (Granada) appears to show that field mice base their diet on holm oak and pine seeds, causing a deterioration of the habitats and an extension of scrubland in the forests. Science Daily
Articles in ‘Spanish rodents’
The Junta del Castilla y León have confirmed 42 new cases of tularemia (also known as rabbit fever) among the population, in all probability trasmitted directly and indirectly by common voles after the explosion of their population in the region. So far in 2007, a total of 200 people have caught the disease, endemic to the region, though last year there was only one case. El Pais See also Explosion of common vole population in Castilla
Wikipedia notes on tularemia “The disease has a very rapid onset, with headache, fatigue, dizziness, muscle pains, loss of appetite and nausea. Face and eyes redden and become inflamed. Inflammation spreads to the lymph nodes, which enlarge and may suppurate (mimicking bubonic plague). Lymph node involvement is accompanied by a high fever. Death may result”
Note: with antibiotics tularemia is not usually life-threatening though the recovery period takes time.
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”
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.