They occupy pretty much every block, and at times seemingly every tree in Kalispell, but how well do you know your friendly neighborhood fox squirrels?

For starters, they’re not native to Montana but still they have managed to establish prolific populations in towns across the state, mostly through intentional introductions that are, by the way, illegal.

“People like these animals,” said Kerry Foresman, author of “Mammals of Montana” and a professor of biology at the University of Montana. “Periodically, they’ve brought them to towns in Montana and they do really well here.”

In Missoula, the earliest introductions were in the 1930s and 1940s, said Foresman, citing a 1937 Missoulian article about squirrels introduced from Wisconsin. But there are stories of further introductions in the 1960s, including one involving a physician from the Midwest.

“He liked them so much that he brought some with him and released them,” Foresman said.

Similar tales apply to Kalispell and most other Montana towns with something important in common for the fox squirrel: the presence of introduced hardwood trees. The maples and elms along Kalispell’s streets easily outnumber native conifers, to the advantage of fox squirrels and the disadvantage of native red squirrels, the chirping forest species known for scolding hunters and other interlopers in their territory.

“People planted hardwoods in towns and fox squirrels are associated with hardwoods,” Foresman said. “They’ve done extremely well and they’ve displaced red squirrels that prefer pine cones.”

For some folks, fox squirrels can be a nuisance. They’re known to raid bird feeders and cause other problems.

“They’re not as benign as people think they are,” said Dwight Bergeron, a biologist for Montana Fish, Wildlife and Parks who specializes in non-game species. “They’re a fairly substantial predator on nestlings and eggs from local birds.”

Bergeron said he’s heard stories about people witnessing squirrels destroying bird nests and that alone can make them unwanted.

“It’s sort of like the turkey issue,” Bergeron said. “You have one neighbor who hates them and one neighbor who loves them, so you get conflicts. I think the same thing happens with squirrels.”

The critters can be entertaining with their twitchy tails, cheeky vocalizations and social interactions. Dogs across the state have long been tormented by wisecracking squirrels that have an uncanny ability to avoid determined canines.

“They really are interesting because they adapt so well to human habitation,” Foresman said. “They’re easy to approach. That’s why they do so well in town and people like to watch them.”

Even though they have been introduced in small groups, Foresman said fox squirrels have managed to maintain healthy genetic diversity. There are two breeding seasons, November through February and April through July, but Foresman said squirrels usually have a litter of two or three young just once a year.

Offspring disperse to new territories that are constantly opening up due to mortality. Over time a population can be widespread.

“It’s not like they are landlocked and inbred,” Foresman said.

Squirrels are known to be busybodies, constantly gathering nuts and tending to their leaf nests, leading to a misperception that they hibernate.

“They don’t hibernate at all,” Foresman said. “The foods that are available, seeds from hardwood trees, they’ll bury those for later use. There’s not a lot of new food available in the winter, so they have to store food from the previous summer and fall. So yeah, they are really active.”

Fox squirrels are among 109 species of mammals in Montana that are chronicled in Foresman’s book. The first edition was published in 2001, and the second edition of “Mammals of Montana” came out in June.

Foresman spent the last couple of years updating the book and he added 500 color photographs that the first edition didn’t have.

Foresman said it is used as a reference for wildlife managers and it has been picked up by schools for biology classes. “But it was written primarily for the general public,” Foresman said.

The book is available in local bookstores and at www.montanamammals.com.

Reporter Jim Mann may be reached at 758-4407 or by email at jmann@dailyinterlake.com.