Earlier last month when my wife and I were on a short hike in the Colorado high country, I heard a distinctive finchy-sort of bird call. The source was fairly nearby on a small rock formation – a little reddish brown bird known as the Brown-capped Rosy-Finch. I had not seen one of these uniquely alpine birds since we moved to Tennessee 13 years ago. In the summer they are found only on the alpine tundra, where it is too cold for trees to grow, in the highest reaches of the Rocky Mountains of Colorado and New Mexico. In the winter they migrate a short ways down slope to the adjoining foothills.
We and the little chirping bird were in a rolling, green highland dotted with lingering, July snow fields and carpeted with riotously-blooming wildflowers only a few inches tall. Around us were sheer cliffs, ravines and mountain summits reaching to elevations above 14,000 feet. Some of the clouds floated by below us, drifting upslope to envelope us in cold fog.
Other than the Rosy-Finch, the bird life was sparse. American Pipits sang and did courtship acrobatics overhead, an occasional Horned Lark flew by and Northern Ravens croaked in the distance. This is a hard place to make a living, frigid and snow-bound most of the year, and few species of plants or animals succeed. A bleak winter outing in Tennessee would probably turn up about 10 times as many bird species as I saw on the tundra at the height of summer.
Most of western North America shows a similar pattern to this. In any given patch of forest, desert, prairie, chaparral or tundra, you will find fewer species than you likely would find in a similarly-sized patch in the southeastern states. The West is a land of extremes. In the era of modern conveniences, the West can seem like an idyllic place to live with sunshine, fresh air, no mildew and few bugs. But for wild plants and animals (as well as the original human inhabitants) it is different and challenging. The warmth and the water are rarely in the same place, so you may find yourself either buried in winter snows or desiccating in the desert.
These climate extremes are also packed right next to each other. Moving a few miles up the mountain can change your world as much as if you moved from Tennessee to Greenland. If you are a bird or a bug or a tree, one lifestyle strategy might work for you across the entire length and breadth of Tennessee. In much of the West, it will only work within narrow belts of elevation and climate, sandwiched in by places that are much less hospitable.
But there is a paradox here. If you flip through your North American bird book, you might get the impression that there are actually more species of birds in the West than in the East. And you would be correct. The total bird list for Colorado is considerably longer than the list for Tennessee. The top birder in the Colorado county in which our Rosy-Finch was chirping has seen more bird species in just that one single county than the top birder in Tennessee has ever seen in this entire state.
How can this be? How can the West have more birds and fewer birds at the same time? It is the flip side of the Land of Extremes. Each one of those narrow belts of elevation and climate (often called a “life zone”) has its own distinctive flora and fauna. At any given spot on the mountain you will find fewer birds than you would at a random spot in Tennessee. But if you travel all the way from the bottom of the mountain to its top, you will pass though many different life zones, each with its own characteristic plants and animals. So when you tally up your entire list for the whole mountain, you might have a pretty good final total. Now do the same thing on a different mountain a few hundred miles away, and you will add even more.
That one Colorado county I mentioned ranges by more than 9000 feet in elevation and spans (by one way to count them) seven life zones from prairie to forest to tundra. On the plains you might see Blue Jays and Black-capped Chickadees. In the foothills there are Western Scrub-Jays and Rock Wrens. Higher up you will almost surely encounter Steller’s Jays and Mountain Chickadees. In the subalpine forests a Gray Jay might squawk at you while the Hermit Thrushes sing. And above tree line you can search for a White-tailed Ptarmigan; but be aware that they look almost exactly like rocks in summer and snow in winter!
You’ll never find a Gray Jay on the prairie or a Blue Jay on the tundra. But you can find them all within a few miles of each other; though it may take you a couple of hours on steep winding roads to cover those “few miles.”
So, ironically, since the West is such a hard place to live and filled with environmental extremes, many more species of plants and animals live there in the region as a whole. Each one is adapted to a fairly narrow life zone, but there are many different life zones all jumbled across the rugged landscape.
Biologists use the term “biodiversity” to describe how varied the plant and animal life in an area is. A while back, I wrote about the importance of the “habitat mosaic” in Tennessee in creating the high biodiversity here. An intricate and complex pattern of ponds, streams, fields, forests and edges here gives us the highest biodiversity, whether this is created by human hands or by windstorms, fires and beavers. In the West, this landscape mosaic is on a much larger scale. It’s not the beaver pond and the woodlot, it’s the mountain range and the desert basin.
Bill Pulliam got started in birdwatching by his junior high science teacher in 1974, and has been an avid birder ever since in 48 U.S. states and 7 foreign countries. He is currently the Tennessee editor for eBird, a online project that compiles millions of observations from tens of thousands of birders around the world.