Ah, those switchback roads.

We were in a van, on a birding tour with about a dozen Minnesotans, some of us less confident in our driver than others. We were on a zigzag gravel road, climbing up a mountain toward Chiricahua Peak.

Jutting out of the Sonoran desert in southeast Arizona are mountains called sky islands. These include the Chiricahuas. They rise to heights of more than 9,000 feet.

Conquering that road, the birds you see as you climb are different from those in the desert below. It gets cold up high. At the top you might need mittens and a warm hat on what on the desert floor is a sweaty day in August.

Every thousand feet you gain in elevation is equivalent to being 300 miles farther north. The tiny town of Portal is where we began our ride. Portal is about 1,600 miles from Great Falls, Mont.

Climb a bit over 5,000 feet up that Arizona mountain and the weather is suitable for Montana. Weather can define habitat. As you climb, bird species change according to habitat, as they would if you drove north.

We can experience that here in Minnesota. Drive from Minneapolis to International Falls, about 300 miles north. You’ve gained the equivalent of 1,000 feet in elevation.

Things are different in far northern Minnesota, where you’ve entered a different biome, the boreal biome.

Biomes are naturally occurring communities of animals and plants found in a particular habitat. In the boreal biome, you can see boreal chickadees, evening grosbeaks and spruce grouse, among other boreal specialists. These are species you won’t find in Hennepin County.

Incidentally, there is boreal biome high on that Arizona mountain. Scientists say the birds stayed in habitat maintained by the high-elevation climate as North American glaciers retreated.

Every living plant or animal has a temperature comfort zone. Some animals or plants are more sensitive than others. For vegetation, in some cases, a few hundred feet higher or lower might be all that is needed to impact temperature and change plant species.

Birds certainly move with more freedom, but for breeding purposes birds are biome-particular.

Scientists have found an ongoing significant but varied shift by birds to the north and to higher elevations. It’s getting warmer below. Birds that are habitat specialists are necessarily slower to make the moves; habitat lingers.

Some years ago, ornithologist Dr. Jeff Price wrote a paper predicting what would happen to Minnesota bird variety as biomes change. He said that eventually we would lose more than half of our breeding warbler species. They would be driven into Canada by a changing landscape.

There will be similar movement up and down our bird checklists.

Other bird species will move into Minnesota from the south. Our cardinals began doing that about 100 years ago. Milder winters helped cardinals. So did we, dotting our landscape with seed feeders. Warblers eat insects, so feeders won’t help.

Those birds will still be with us, just at the end of a longer drive.


Read Jim Williams’ birding blog at startribune.com/wingnut.