Lewis's closeup view of Clark's nutcracker is certainly complete, and his recognition of its membership in the crow family is correct. But there's more to the story, and it's still being written. This bird's ancestors have been squalling around the Rocky Mountains boisterously for at least twelve million years, just doing their job. Returning a favor. Growing trees. In fact the Clark's nutcracker is wedded for better or worse to the whitebark pine.
The whitebark pine is tough. It lives in dry, rocky soils on exposed slopes and ridges in the sub-alpine zone of the Northern Rockies, up to about 10,000 feet, and it's designed to withstand the rigors of life at those heights. Some of the whitebark pines standing on the ridges along the Continental Divide today may have been many years old when the expedition passed by. But this tree has a problem. It produces seed-cones about once every four or five years, which don't open until they decay, which can take a long, long time up there.
Clark's nutcracker is a similarly hardy creature; with luck it may reach the hoary old age of twelve years or more. It likes living at subalpine elevations, and nesting in whitebark pines (in February!), but to survive it needs fatty foods such as the seeds held fast in the whitebark pine's cone. So the nutcracker is equipped with a bill like a crowbar, to pry them from the cones.
In a pouch in its throat, the bird can carry up to several dozen seeds to bury in the ground for a later appetite—a whitebark seedbank; a nutcracker foodbank.
The bird hides its seeds in a number of caches spread out over a radius of up to several miles. On average, it eats only about two-thirds of the seeds it saves, but it buries them all at just the right depth for some of the leftovers to germinate. This explains why whitebark pines often grow in clusters.
There are other dividends in this fruitful companionship. Together, the bird and the tree create a home for other animals: red squirrels, grosbeaks, and Steller's jays. Grizzly and black bears dig up the nutcracker's leftovers when they prepare for hibernation. For thousands of years, and until long after Lewis and Clark were gone, even native people shared the whitebark pine's wealth, grinding the seeds into rich flour.
Since the early 20th century, however, people with different values have changed the terms of this nuptial contract between bird and tree. Trees have come to be thought of as cash crops, and fire, nature's household cleanser and garden herbicide, has been an enemy to be suppressed. As a result, subalpine fir trees—weeds of the woods, having no commercial value—have moved in and taken over the whitebark pine's neighborhood. The whitebark pine isn't commercially important either, so few people notice when the whitebark loses ground, or when Clark's nutcracker goes hungry.
Better is coming to worse.
Ronald M. Lanner, Made for Each Other: A Symbiosis of Birds and Pines. New York: Oxford University Press, 1996.