Hiding tens of thousands of pine seeds each year makes the nutcracker a prolific natural forester.
One sunny day in the Sierra Nevada mountains of California, Diana Tomback met her first Clark’s Nutcracker. While resting under a pine tree, he noticed a bird tearing scales off a pine cone. Its persistence in stabbing the cone with its beak, removing the scales and extracting individual pine seeds mesmerized her. He had to know more, and when a ranger passed by, Tomback demanded information. That bird, the ranger said, was a “pine crow,” and the tree was a whitebark pine.
When she returned to graduate school, she was determined to find out more. “This bird, its behaviors and interaction with the whitebark pine completely consumed me,” Tomback says. A little research revealed that this ‘pine crow’ was a Clark’s Nutcracker. But he couldn’t find much else. The Eurasian nutcracker had been studied in Russia, Germany and France, but little was known about its North American cousin.
“I realized: Oh my gosh, what an incredible bird and interaction to study,” she says. So Tomback dedicated himself to the cause. Since the 1970s, Tomback, now an ecologist at the University of Colorado, Denver, has published dozens of papers on Clark’s nutcracker. Along the way, he discovers that the birds are more remarkable than he imagined. Clark’s nutcrackers are winged forest rangers whose penchant for hoarding seeds contributes to the growth of new pine forests.
A Desire for Cones Clark’s nutcrackers are experts in the difficult art of freeing the seeds from cones. Each cone contains dozens of seeds, which are inaccessible to most animals until autumn, when the cones open and spread their protective scales. But the Nutcrackers don’t have to wait. As the stiff, immature cones become available each July, they dig their strong, piercing beaks between the scales to loosen and tear off bits of seed.
It’s not an easy job. Clark’s nutcrackers spend so much time chopping up pine cones that the sticky resin sometimes turns their gray feathers a reddish purple. But the prize is worth it: pine seeds are a nutritious food, packed with fat, protein, and carbohydrates. They are so tasty that it doesn’t take many to satisfy a nutcracker’s appetite, and that’s when the bird’s habits get really interesting.
Photo: Marshal Hedin/Flickr CC (BY-SA 2.0)
Hide and seek While other birds prepare for winter by feasting and fattening up for hard times, these elegant gray corvids use their landscape as a larder. After a Clark’s nutcracker fills with pine seeds, it stores the rest, more than 100 pine seeds at a time, in an expandable pocket under its tongue.
The bird then flies through the forest, burying clusters of four or five seeds in the ground; During peak pineapple season, it will store up to 500 seeds per hour. By late fall, each nutcracker has hidden tens of thousands of seeds, a food source it depends on all winter.
Surprisingly, the birds manage to find their hiding places later. They often hide seeds near the base of tree trunks, a tendency “that may play an important role in their spatial memory system,” Tomback says. Landmarks help nutcrackers remember the precise locations of hiding places, so they can retrieve and eat seeds when the trees have no cones and the weather turns cold.
“These birds probably remember up to 10,000 caching locations” at any given time, says ecologist Mario Pesendorfer of the Cornell Laboratory of Ornithology. But his memory fades over time. Within nine or 10 months, many uneaten seeds lie forgotten beneath the forest floor.
Nutcracker-winged foresters often bury their seeds at the perfect depth for germination, and with time and a little luck, the abandoned seeds will sprout and grow into new trees. In this way, their overzealous seed hiding means that Clark’s nutcrackers play a vital role as foresters, planting new generations of pine trees that conveniently sprout from excess supply.
Crucially, birds will hide seeds up to 20 miles away from their home trees. By doing so, they help trees expand their territory to new areas. As development continues to fragment forests and climate change demands rapid migration, “animals that move between patches of habitat are increasing in importance,” Pesendorfer says.
Nutcrackers have an especially close relationship with the whitebark pine. Even in autumn, white-barked cones do not open on their own; The seeds are trapped behind tightly closed scales. It’s largely up to Clark’s nutcrackers to release those seeds with their hammering beaks and then help spread them. Additionally, unlike other pines, whitebark seeds do not have “wings” that allow them to ride gusts of wind across the landscape. Instead, the seeds and cones seem optimized for a nutcracker’s beak, and as such, the trees depend on the birds’ forgetfulness to reproduce.
The relationship has served both species well, but researchers are increasingly concerned that whitebark pines are now in decline. A deadly fungus called white pine blister rust is spreading through western pine forests. At the same time, mountain pine beetles chew through the trees, a problem that is worsening with climate change. The loss of pinecones should not threaten Clark’s Nutcrackers; They can feed on a variety of seeds and cones along with insects and fruits, so they are safe for now. But as whitebark pines disappear from the landscape, they will produce fewer seeds, and the birds that once helped them proliferate may not be able to store enough caches to support the tree.
However, it is possible that birds could help whitebark pine recover. Human foresters are now studying how to attract Clark’s nutcrackers to assist in forest restoration. As fantastic as it sounds, this is not an unprecedented effort. Since at least the 1950s, German foresters have harnessed the abilities of another disperse-hoarding corvid, the Eurasian jay, to their advantage. Instead of doing the hard work of replanting oaks, they put out buckets of acorns and “let the jays do their thing,” Pesendorfer says. It is estimated that jays plant up to 1,600 oaks per acre. If Clark’s nutcrackers could do the same, but with blister-oxidation-resistant whitebark pine seeds, they could be the saviors of western pine forests.