VITTORIO VENETO.The mysterious and disturbing death of mice is due to accidental causes related to overabundance. A phenomenon that is affecting part of the Veneto, with prevalence in the Vittoriese, but also Friuli-Venezia Giulia. Chain deaths, therefore, are a completely natural phenomenon. This is supported by Dr. Luca Lapini, zoologist of the Friulian Museum of Natural History in Udine, consultant to various institutions, universities, Italian and European museums. Here is his thought.
Virological, bacteriological and toxicological investigations on mouse carcasses have given negative results. So what explanation can we give to this exceptional die-off recorded in recent months?
“It is a phenomenon that we have been following for years. It is called pullulation, that is, sudden population increase and it affects many species of rodents. This year seems to be particularly spectacular. Animals fall into rivers and lakes and drown, but they also die from other accidental causes. In Val D’Arzino, in Friuli-Venezia Giulia, 300 have been found, drowned in the waters of the stream of the same name ».
Why does this happen?
«It is a very complex phenomenon, which varies from area to area, so much so that it is difficult to explain it in a univocal and generalizable way. In our mountains, the pullulations are conditioned by a particularly abundant production of heavy seeds by beech and spruce. It is defined as a “forest pasture”. It occurs repeatedly and continuously, with cycles of two, five, ten years. There are very robust data for the Cansiglio Forest which confirm the strong link between forest grazing, the abundance of rodents and the reproductive success of some predators ».
But the causes of all this?
“They are probably related to the rainfall regime. The stress that comes from dry summers stimulates a particular production of vegetative buds, with a subsequent large production of heavy seed. Moreover, very dry springs-summers favor the anemophilous pollination of beech and spruce, to the point of supporting even more an already well-established fruit production ».
How do these weather conditions affect rodents?
«In late summer-autumn some forest rodents take advantage of it. If the following winter is warm enough, these animals suffer very little autumn and winter mortality. In spring, their number becomes above average. Both for their number and for the abundance of food, they begin to reproduce en masse, triggering phenomena of pullulation that can surprise for the abundance of animals. However, the collapse of these overcrowded populations is very rapid, both due to the rapid increase of predators that use them as a source of food, and to the overcoming of the carrying capacity of the environment ».
Let’s go back to these impressive deaths of mice observed in many municipalities of Veneto and Friuli. The rodents were found in lifeless groups in public and private places and all with no apparent signs of suffering. Can you explain how they died?
“A great many have drowned. The reasons are related to random movements that lead to falling into the water, in some cases they drown because they cannot get out. These are animals that if they remain in the water for a long time undergo hypothermia ».
But they were found in courtyards, squares, public places.
«The fact that they enter towns or cities is normal and is linked to the need to explore new environments, looking for new spaces to colonize, they enter every available hole. Mice found along the mountain trails were attacked by predators. Predators, in conditions of great abundance, kill more than they are able to consume. Phenomenon known as surplus killing. They attack them, but they don’t eat them. On the plains, in this situation of abundance, they were run over, or fell into the water, but they were also hunted by the house cats. They also do not eat them if they are already full ».
Didn’t they die of hunger?
«I have many doubts. These are herbivorous species that feed on shoots, insects. To say they died of hunger is a leap of faith. The analyzes carried out excluded diseases, the most likely thing is that they died from accidental causes linked to the overabundance ».
A “mass suicide” was also hypothesized. There was talk of a phenomenon similar to that which pushes lemmings, small rodents in the arctic areas, to commit suicide en masse by throwing themselves into the sea from the cliffs when the population expands beyond the sustainable limit of food resources.
“This is a hoax. Suicide does not exist in the logic of a living being. That it is not homo sapiens ».
What have been the most recent pullulations?
«The most recent swarm in the mountains between Veneto and Friuli dates back to 2012 and has affected a very large area. The previous proliferation of which we have memory in the area is in 1993 ».
What is the advice you want to give to the population?
“There is no danger. Absolutely avoid rodent control carried out with coumarin products that poison the entire food chain. No health alarms ».