Birds
Clark's Nutcracker
Nucifraga columbiana · also called Clark's crow, woodpecker crow
In the high mountains of the American West, a pale grey crow spends every autumn burying pine seeds, one small handful at a time, until it has hidden tens of thousands of them across the slopes. Through the winter it digs most of them back up. The ones it misses grow into the next forest.
Overview
Nucifraga columbiana lives in the high conifer forests and treeline of western North America. It feeds mainly on the large seeds of mountain pines, and carries them in a pouch under the tongue that holds up to about 150 at once.
The caching machine
A single bird buries an estimated 30,000 to 100,000 seeds a season in thousands of small caches, often kilometres from the source and on slopes that clear of snow early. Months later it relocates most of them using landmarks and an enlarged spatial-memory region of the brain.
It plants the forest
The whitebark pine has co-evolved so closely with the nutcracker that its cones never open on their own — it relies almost entirely on the bird to plant its seeds. The nutcracker nests in late winter, raising young on the previous autumn’s stored seeds.
Status
Least Concern but locally declining as whitebark pine collapses from an introduced blister rust, beetle outbreaks, and a warming climate.
Clark's Nutcracker: common questions
How does Clark's nutcracker remember where it buried so many seeds?
With a memory system that is exceptional even among the famously clever crow family. Over an autumn a nutcracker makes thousands of separate caches spread across many square kilometres, then spends the following winter and spring digging them up, often through a metre of snow and long after the landscape has changed. Laboratory and field studies show the birds navigate to caches using the geometric relationships between landmarks such as boulders, stumps, and trees, and that the part of the brain used for spatial memory, the hippocampus, is enlarged relative to other corvids. They do forget or lose some caches, and they also re-cache seeds to keep them from spoiling or being stolen.
Why does the whitebark pine depend on this one bird?
The two have evolved together to the point of mutual dependence. Whitebark pine produces large, wingless, energy-rich seeds inside cones that stay closed at maturity, so the seeds cannot simply fall or blow away. Clark's nutcracker is the animal that opens those cones, carries the seeds, and buries them in exactly the kind of open, well-drained, early-melting ground where whitebark seedlings grow best. Seeds the bird does not recover become the next generation of trees. Without the nutcracker, whitebark pine has almost no way to regenerate, which is a serious problem now that the tree is declining steeply from disease and beetles.
Is Clark's nutcracker a woodpecker?
No, though early names for it included woodpecker crow because of its grey-and-black plumage, its stout pointed bill, and its habit of clinging to trunks and hammering at cones. It is a member of the crow and jay family, most closely related to the Eurasian spotted nutcracker, which has a similar seed-caching lifestyle with Arolla pine in the Alps and Siberia. The two nutcrackers are a classic example of the same ecological role evolving on different continents.
Why does it nest in the middle of winter?
Its whole breeding schedule is built around its stored food. By nesting in late winter, a pair can feed themselves and their chicks on the seeds cached the previous autumn, which are still abundant and easy to reach before the deep snow melts and before the new year's cone crop is anywhere near ripe. It is one of very few songbirds that regularly incubates eggs in freezing conditions, and unusually both the male and the female develop a bare brood patch and share incubation closely, so the eggs are never left exposed to the cold.