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Migrating birds appear to follow our rivers

Turkey vultures are but one species of bird which appear to favor river corridors during migration. Keith Corliss

Take a look at a map of the local area and a person finds quite a few towns situated along or near a flowing piece of water. The reason is obvious. The early settlers needed a ready water source. Plus the coal-fired steam locomotives couldn't move without steady water supplies. So rivers and streams were seen as a critical necessity.

Today it's somewhat different. The towns are still around of course, but we see our rivers from somewhat different perspectives. Currently, they are sources of much anxiety as most have left their banks and are dangerously wandering overland. At other times they might be a recreation destination for fishing or canoeing. Some look at the rivers with disdain as water clarity falls far short compared to something a person might find in the Rockies. They represent boundaries between properties, counties, even states. To animals, the water courses and their accompanying riparian habitats are refuges, sources of food and shelter.

Another way of thinking about the various streams of the Red River Valley is as migration corridors for birds. The Red River is not huge from a national perspective. The Sheyenne, Maple, Wild Rice and Rush are even smaller. But they do appear to serve as fairly significant metaphorical highways for various flying birds. Not Interstate highways perhaps, but almost certainly U.S. or at least state ones.

Of the four major flyways spanning the continent, the Red River Valley sort of straddles two--the Mississippi and the Central. But I don't believe we should overlook the valley as a potentially rich migration route.

I thought about this one day last spring while waiting for my son to finish baseball practice at Fargo's Lindenwood Park. In just an hour's time I counted several migrating broad-winged hawks, turkey vultures, and other raptors. It seemed the river course was being used as a sort of map for the creatures.

Let's throw a caveat into the idea before we proclaim our prairie rivers as definitive migration lanes however. Not all bird species appear to use them; waterfowl being the obvious exception. The geese and ducks aren't necessarily looking for wooded corridors. They seek open spaces with pooling water for the most part. There are other prairie species which shun the woods as well. But might they still reference them as landmarks while flying?

There's another factor which bears some critical thought from a scientific standpoint and that is bias. It certainly enters the equation and is worth considering. Most of us, including me, spend the majority of our time close to a river. We live near them after all. If I see 10 Cooper's hawks move along a river in an hour would I have seen a similar number had I been standing in the middle of a farm field, miles from a river? Probably not, but I can't be positive. It's the old if-a-tree-falls-in-the-forest thing.

Yet I believe our rivers are used by many migratory species as pathways. The water itself may be a draw for some (wood ducks, ospreys, bald eagles, etc.) but more important to the birds is the physical nature of the landscape. Passerines - those songbirds currently venturing north - are almost certainly attracted to the woods along the rivers. For soaring birds it's the terrain. Moving water carves channels into the earth creating slopes for air to lift, the shallow Red River Valley notwithstanding. It's these cushions of rising air upon which the long-winged soarers ride.

Migration remains a less than complete science. Whether it's hard-wired into instinctual portions of the animals' brains or simply a convenient course made available by happenstance is a mystery I don't think we understand. More likely it's a combination of a lot of things. Night sky pattern, magnetic fields, wind, weather systems, sun angle, scents, and sounds have all been found to influence bird movements in some species. But even our meek prairie rivers enter into the mix somewhere too. At least I think they do.