Flight Lines: Ranges not static, never have been
There is a mistake commonly committed by birdwatchers of all stripes, particularly those just starting out. That is treating the species range maps depicted in the various field guides as though they were chiseled in stone, irregularly shaped blobs of color or outlines corralling the species in question into a tidy well defined border. That is not the case and it never has been.
Fittingly, I found a nice slightly used copy of Robert Janssen's Birds in Minnesota, published in 1987, at a used book store recently. Janssen is one of the titans of birding in Minnesota having spent decades tirelessly traveling the state and keeping impeccable records while doing so.
He wasn't the first to put out such a volume. That honor belongs to Dr. Thomas Roberts, who published The Birds of Minnesota in 1932. Roberts's book counted 320 species. By the time Janssen published in 1987, the list had blossomed to 400 prompting him to give as the reason for writing the book as, "The need to keep current on this information and create a continuous historical record of these changes..."
It's a human trait to want to make sense of the world around us, to define it, to eliminate the gray areas and put everything neatly in its place. That's all well and good but our lifespans, in the big scheme of things, are so pathetically short that we fail to appreciate just how quickly nature ebbs and flows.
The areas (or ranges) we expect to find certain plants and animals will not be exactly the same ten years from now, perhaps not even next year. All manner of external pressures pull, tug, push, shove, and outright erase species every day. Chief among these is habitat change/loss. The pastures where one may have heard larking chestnut-collared longspurs this summer may very well be plowed under and planted to soybeans next year, never to see a longspur again.
A growing season which appears to be lengthening is allowing for plants and animals to survive farther and farther north. As important as healthy nesting habitat is to birds, a strong argument can be made that wintering habitat might be even more vital to the long term health of a population. For some species, it might not matter that their summer range is intact if their winter range in the forests of Central or South America disappears from the landscape.
I can cite many examples of even short term range changes that have occurred in a rather brief period of time. Take double-crested cormorants, for instance. Before our local wet cycle began in 1993, cormorants were not nearly as numerous as they are today. The tremendous number of dead trees (from flooded wetlands) has provided roosting sites for this aquatic species all over the area.
Old timers speak of a rather robust population of red-headed woodpeckers at one time. No longer. This migratory woodpecker is dependent upon a certain type of dead wood habitat that the invasive European starlings apparently like too, to the woodpecker's detriment. It's an uncommon treat to find a red-headed woodpecker today.
How do we explain the lesser black-backed gull phenomenon? This European gull was first identified in the state not all that many years ago. While still not common, it is nonetheless an expected species every year now in North Dakota including Cass County.
There are many, many more examples of the highly fluid state of avifauna on the local level as well as a national, even global one. Of course, it has always been this way. It's never been a static state of natural affairs, only a shifting fluid one.
When glaciers sat a mile deep over Fargo a few thousand years ago there were no nesting birds. While the ice ages put tremendous pressure on species ranges for hundreds of years the glaciers have disappeared for now. Less obvious stressors are ever-present, however, and they will continue to reshuffle the ranges of plants and animals, helping some, hindering others; as they have for millennia.
Janssen's book might even be ready for a few tweaks. He's got bald eagles listed as "uncommon spring and fall migrant throughout the state." They are everywhere today. Eurasian collared-doves? This fairly recently arrived Old World invader is not even mentioned. His book was a snapshot of the bird landscape in 1987. A lot has changed in 30 years.