December 6, 2012 A bird and a pine: An inseparable couple
The amazing whitebark pine (Pinus albicaulis) reach ages in excess of 1,000 years old. It lives in the harsh environs of the Rocky Mountains and has cooperatively co-evolved with a bird – known for its extraordinary memory – called the Clark’s nutcracker.
White bark pines can reach heights of 65 feet, but more usually they are recognized as a stunted multi-stemmed tree. Named after its whitish bark with scaly plates on older trees, its needles grow in bundles of five and egg-shaped, sticky-with-resin purple cones, take two years to ripen. The wingless seeds are large and filled with high concentrations of fats and proteins. Cones mature in late August, but do not open widely enough for the seeds to fall out. If the seeds over-winter in the ripened cones, by springtime they become moldy and turn rancid. So how does viable seed get out of white bark pine cones?
Clark’s nutcrackers belong to the 113-member group called the Corvids. Corvids have unusually large brains compared to all the other 10,000 bird species. They eat some insects and occasionally a bit of carrion. But it’s their chisel-like bills that are specially adapted to ripping into white bark pinecones and with precision extracting the large protenacious seeds. These seeds, as a primary food source, enable the throaty squawks of resident Clark’s nutcrackers to live year-round in the otherwise inhospitable environment of the Rocky Mountain alpine (above tree line).
This is a story of a mutual relationship between bird and pine, offering insight into the marvels of Mother Nature. Together, Clark’s nutcrackers and white bark pines build high elevation ecosystems.
Nutcrackers start to feed on white bark pine seeds in mid-August. They chisel into the purple, pulpy cones and extract seeds, one at a time. They store the seeds in a sublingual pouch in the floor of their mouth, underneath the tongue. This pouch can hold as many as 80 seeds. The August and September seed harvest must sustain the birds and their offspring, for the coming 10 months.
The Clark’s nutcrackers then carefully deposit the seeds, one at a time and up to 15, 1 inch deep into the soil. Occasionally these caches are close to the tree where the harvest took place, but more often it’s up to 6 miles away. Seeds are buried in open areas and in recently burned-over high-elevation forests. Some of those openings remain windswept during the long winter months. Others can have over six feet of snow covering the cache and I have observed Clark’s nutcrackers burrowing into deep snowpacks to retrieve white bark seeds.
One bird can cache up to 98,000 seeds in over 30,000 sites. About half those seeds will be recovered by Clark’s nutcrackers. Multi-stemmed white bark pines denotes a cache was not retrieved and that several or more seeds sprouted at the same time and have grown together.
How does the Clark’s nutcracker locate all of its caches? Experiments have clearly demonstrated that these birds, like other Corvids, have excellent memories and in fact remember where they placed the seeds. They use a system of triangulation to reference where caches are located. That is, they use a tree, stump, rock, log or other landmark and remember the angles between the caches. Their memories, especially long-term, are remarkable, since they are able to recover seeds some 10 months after storing them. They must also use other cues to assist them because snow modifies the landscape.
White bark pine seeds are also an important food source for ground squirrels that also live full-time in the alpine of the Rocky Mountains. They too harvest the cones and take them to large caches called middens. In addition, ground squirrels raid Clarks’ caches and relocate seeds.
In the autumn and occasionally the springtime, black and grizzly bears raid ground squirrels middens. I have watched bears gingerly extracting the delectable white bark seeds. Prior to hibernation a sow must add about 7 inches of fat around her tummy or 99 pounds of body weight, in order to give birth – while she’s hibernating – to cubs. So the white bark pine seed is a very important food source for many different big and small alpine and subalpine animals.
Soon after the spring snow-melt, white bark pine seeds germinate and grow 8 inches deep tap roots. White bark pines require full sunlight – they are shade intolerant and cannot grow under other trees. White bark pines change the micro-climate, causing warmer winter and cooler summer under their cover. Over time, openings along the high elevation landscape are filled in by white bark pines and clumps of young trees form new forests high in the mountains.
In time, Englemann spruce, which require some shade, seeds itself into the under-story of the white bark pine forests. Other tree species like subalpine fir follow soon thereafter.
Some trees die young and their wood serves as a decomposing base to feed bacteria, fungus and wood boring insects, which assist in the breaking down of wood and making new soils. Other, like old white bark pines, become victims to pine bark beetles and die but remain standing upright for another 100 years. Woodpeckers, nutcrackers and other cavity-nesting birds use these trees for roosting and nesting. These forests are occasionally used by big game animals like mule deer. In the autumn, finches, siskins and crossbills forage in the Englemann spruce treetops.
In the wild, Clark’s nutcrackers can live for 12 years. They can fly at speeds of 30 miles per hour carrying a load of seeds than can exceed 20 percent of their body weight, for distances up to two miles. About 22 species of high elevation pines worldwide depend on a dozen or so Corvids to help disseminate their seeds, create forests and habitats for many animals.
Eventually, one hot and muggy summer afternoon a bolt of lightning ignites the forest. The assiduous Clark’s nutcracker will return to replant the forest, feed other animals, and recreate the tenacious forested mountain ecosystems of Rocky Mountains.
Text © by Dr Reese Halter 2012. All rights reserved.
Tags: Australian Broadcasting Corporation, Australian Conservation Foundation, Avaaz, black bears, california, Clark's nutcrackers, Colorado, conservation biology, crossbills, Defenders of Wildlife, Denver, Dr Reese Halter, Ducks Unlimited, ecology, ellen degeneres, Englemann spruce, environment, Environmental Defense Fund, finches, Green Peace, Grist, grizzly bears, ground squirrels, Idaho, John Denver, leonardo dicaprio, London Olympics, Los Angeles, Muir Woods National Monument, mule deer, National Audubon Society, Natural Resources Defense Council, nature, Nature Conservancy, New Mexico, Oprah, Oregon, Peta, Portland, Rocky Mountains, San Francisco, science, Seattle, Sierra Club, siskins, Steve Irwin, subalpine fir, Ted Danson, Treehugger, triangulation, Wyoming, Yellowstone National Park, Yosemite National Park