One of 3 new bird species described by Alexander Wilson from specimens collected during the historic Lewis and Clark expedition, Clark's Nutcracker was feeding on pine seeds and was mistaken for a woodpecker when first seen by Captain William Clark on 22 August 1805. Lewis and Clark did not collect a specimen until the following year on the expedition's return journey along the Clearwater River near Kamiah, Idaho ( Davis and Stevenson 1934 ).
Clark's Nutcracker inhabits the high montane regions of the western United States and Canada, preferring coniferous forest dominated by one or more species of large-seeded pines. Its year-round diet consists primarily of fresh and stored pine seeds. Nestlings and juveniles are fed seeds from stores as well. The morphology, behavior, and annual cycle of the nutcracker is closely tied to this specialized diet. Conversely, several pines that depend on nutcrackers for seed dispersal show specialized cone and seed traits for this interaction: whitebark (Pinus albicaulis), limber (P. flexilis), Colorado piñon (P. edulis), single-leaf piñon (P. monophylla), and southwestern white (P. strobiformis). Seed dispersal by Clark's Nutcracker has resulted in a commonly occurring tree cluster growth form in 3 of these pines and has altered their genetic population structure in comparison to wind-dispersed pines.
Notable features of Clark's Nutcracker include a sublingual pouch, used to transport seeds to cache sites; a long, sharp bill, used to open conifer cones, extract seeds, and place seeds in caches; and an incubation patch in the male as well as the female, allowing the male to incubate eggs while the female retrieves seeds from her caches. In addition, a remarkable spatial memory enables this species to relocate thousands of seed caches within a year of storing them.
The annual cycle of Clark's Nutcracker is based on the availability of fresh and stored pine seeds. As early as July, this species begins to eat unripe seeds from the new cone crop, usually at upper montane or subalpine elevations. Storage of ripe seeds begins by early September; a few weeks later many birds switch to new seed sources, often by migrating to lower elevations. The nutcracker may continue making seed stores through December, if the seed supply is adequate. During winter, it harvests the few seeds remaining in cones and uses the more accessible seed stores. Nesting begins as early as January or February at montane elevations, despite harsh winter weather. Nestlings and fledglings are fed shelled pine seeds retrieved from stores. In late spring, individuals and families migrate to higher elevations; there, parents and nonbreeders retrieve seed stores made available by snowmelt and take other foods opportunistically. Cached seeds from the previous fall are fed to young. Almost all juveniles become independent by the time the new seed crop is ripe, making their own caches.
Much research remains to be done on Clark's Nutcracker, particularly with respect to its social system, breeding biology, and population dynamics, and in different regions of its range. We owe our knowledge of breeding biology, pterylography, molt, and general food habits to L. Richard Mewaldt ( Mewaldt 1956 , Mewaldt 1958 , Giuntoli and Mewaldt 1978 ), who studied individuals from the northwestern U.S. Best studied (albeit incompletely) are foraging on conifer seeds, seed storage and retrieval in the field, and relationships with pine mutualists, in n. Arizona ( Vander Wall and Balda 1977 ), e. California (Tomback Tomback 1978a , Tomback and Kramer 1980 , Tomback 1982 ), nw. Utah ( Vander Wall 1988 ), and w. Wyoming ( Hutchins and Lanner 1982 ); and seed storage and retrieval by nutcrackers in the laboratory ( Vander Wall 1982 , Kamil and Balda 1985 ).