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.