Q. Black squirrels are predominant (or perhaps exclusive) in Ontario. A Canadian friend recently stated that she had heard that they have “crossed over” into Michigan. Do you know the magnitude of this black squirrel migration?

A. Black squirrels are a variant of the Eastern gray squirrel–the gene for the black coat is recessive. The black variety has recently become more common in Ann Arbor.

Scientists aren’t sure why. Squirrel survival rates depend upon complex combinations of factors, including weather, terrain, and predator populations. Squirrels can potentially live as long as eight years, but in the wild, the average lifespan is only seven months. As a result, the populations we see can change rapidly.