Over the last three decades, Europe's wild boar population has continued to rise. New research suggests their numbers have been buoyed by mild winters brought on by climate change.

Wild boars can tolerate cold temperatures via thermoregulation, but they must consume more food to conserve energy. This puts a strain on available resources and provides a natural constraint to population sizes.

But when cold winters follow mild ones, researchers have found larger numbers of boars are able to withstand the frigid temperatures. Their perseverance is thanks to mast years, increased fruit production by beechnut and acorn trees -- the preferred foods of wild boars.

As the new research out of the University of Veterinary Medicine, Vienna, reveals, mild winters -- and mast years -- are becoming more frequent, bolstering boar numbers.

"There is a sharp increase in the number of wild boars after mild winters," wildlife biologist Sebastian Vetter explained in a press release. "As mild winters are becoming more frequent, also wild boar populations are growing exponentially."

The abundance of boars have been showing up in public parks across Europe, and have been known to invade livestock fields and raid feedlots. They can be quite aggressive toward humans and other animals.

Vetter says counting boars is a difficult and imprecise science. But all the indications point to the animal's ever-increasing presence.

"It is not so easy to determine the number of wild boars in Europe," said Vetter, lead author of the new study on the subject -- published in the journal PLOS ONE. "Therefore we analysed data on hunting bags and road accidents involving wild boar. Doing this we were able to depict the growth of the wild boar population."

But not all wild boar populations are the same. Boars in Southern Europe are smaller, as a smaller body is advantageous during the regions warmer summers. But those same small bodies are less well suited for the winter. For this reason, southern populations require an even milder winter for population growth.

Milder winters have been abundant in the north and south, however.

"Wild boars produce a surprisingly large number of young animals compared to other ungulates," Vetter pointed out. "This enables the strong growth of populations which we are currently observing. Therefore we are particularly interested in the factors that influence reproduction of this species."