There’s a fine article on animal migrations in the November 2010 issue of National Geographic. Most of us North Americans have heard of the seasonal migrations of monarch butterflies, sandhill cranes, and the Mexican free-tailed bats.

But did you know that thousands of prairie rattlesnakes migrate up to 33 miles from an area near Medicine Hat, Alberta? They don’t travel as a group. Hundreds of snakes emerge from a den, then take off in a starburst pattern in all directions.

I read a long time ago that cattle egrets display similar migratory behavior. When a community grows saturated and it’s difficult to sustain the population, the young adults will take off in a starburst pattern, sometimes out over the sea, to find new territory.

Many migrations no longer occur because of encroachment of humans. For example, bison and passenger pigeons once migrated by the millions, but were essentially exterminated in a rather short period of time for sport. (The passenger pigeon is now extinct; with a few exceptions, bison are now fenced in as ranch animals.)

Wiki at this time suggests that squirrels do not migrate, but here is a link to an well-researched piece that documents a number of impressive migrations in the 1800s. ( Squirrel Migrations )

David Quammen who wrote the National Geographic article summarizes biologist Hugh Dingle’s factors that characterize animal migrations. Here are some of them:

Migrations ‘are prolonged movements that carry animals outside familiar habitats; they tend to be linear, not zigzaggy; they involve special behaviors of preparation (such as overfeeding)…Migrating animals maintain a fervid attentiveness to the greater mission, which keeps them undistracted by temptations and undeterred by challenges that would turn other animals aside.’



The above is a photo of a map from the National Geographic article.