Great Basin National Park is for the Birds!

by David Lukas

Early summer along Lehman Creek in Great Basin National Park and, as birders like to say, the trees are dripping with birds -- Clark's nutcrackers, dusky flycatchers, hermit thrushes, western tanagers, song sparrows, yellow warblers. A dipper is doing its thing in the creek. Migration is in full swing and neither vast desert reaches nor remote mountain forests seems to deter these little bundles of energy. How these birds come to be here is the story of the evolution of the Great Basin.

Most species of birds view the landscape of the Great Basin as a series of islands, and migrating birds make dangerous journeys across dry oceans of sagebrush to reach these islands. Two types of islands are especially significant to the survival of birds: lakes or marshes, and pockets of mountain forest. And these are the places we find the greatest number of birds. More properly, these islands are fragments of habitats that once spread across the entire region. Until the end of the Ice Age 10,000 years ago the climate of the Great Basin was cool and wet. Vast lakes covered an area of 28 million acres, and coniferous forests stretched from the Rocky Mountains to the Sierra Nevada.

A steady drying trend dramatically reduced the size of the lakes, and resulted in forests retreating to cool shaded mountain strongholds. As habitats changed, birds have attempted to hold onto old behaviors. Migration is most likely an ancient journey still practiced despite the growing distances between islands.

These distances are insurmount-able for some species, and forest birds especially, tend to stay put and form subpopulations which become unique to each mountain range. Many forest species seem to have originated from ancestral populations in the Rockies, but over time they may evolve into unique Great Basin forms. It is the nature of islands that life there is fragile. Populations are small and subject to catastrophes, extinction is common. Migrating birds have to cross great distances to reach islands, and when they arrive they are hungry and weary. The arrival of migrants is accompanied by frenzied feeding as they refuel for the next stage of their journey.

The scene along Lehman Creek in Great Basin National Park has all the elements of this story. A visitor may not think of these creekside forests as an island but glance into the distance and you realize that this place is truly an oasis. Birds realize that as well, and over time have evolved to either stay put or fly great distances to arrive here. Some migrants continue on, flying from island to island, until they reach a land of continuous forests and abundant water to the north.

This landscape has changed rapidly over the last 10,000 years. No one knows exactly how bird populations have responded to these changes, but it is clear that modern species occupied the region long before the desert arrived. As sagebrush replaced trees, many species retreated to mountain canyons where they carry on their old ways of life amongst relict stands of Ice Age forest. The Great Basin Desert is young and birds are still adapting to this newcomer, crossing it, living at its edges, or settling into a small niche wherever water can still be found.

David Lukas is a naturalist and writer who guides trips in the Great Basin.