Masters of memory
Amazing birds help trees—with staggering feats of remembering
Posted on homepage: 8 June 2022 (GMT+10)
We often think of animals in terms of individual species, but many animals have mutually beneficial relationships with other animals and even with plants. The relationship between the Clark’s Nutcracker and the white bark pine tree is one such symbiotic relationship. Both can be found in the subalpine forest of the western United States and Canada. They are keystone species, meaning without these two species, the landscape would change.
The Clark’s Nutcracker, Nucifraga columbiana, is a grey bird with black and white markings in the family Corvidae, which also includes crows, rooks, jays, and magpies. It is named after the famous explorer Captain William Clark, who helped lead the Lewis and Clark expeditions in 1804–1806.
The nutcracker’s pointed bill is the perfect size and shape to penetrate pinecones of the white bark pine, Pinus albicaulis, and other trees to extract seeds. This is because the pinecones of the white bark pine do not naturally open when the seeds are ripe. This means they are not dispersed by the wind like the seeds of many other trees, so the Clark’s Nutcracker is instrumental in spreading the seed.1 In return, the nutcracker is rewarded with the calorie-dense white bark pine seeds which form the bulk of its diet. The success of these two species is interconnected.
Even though the Clark’s Nutcracker is an important player in seed dispersal for a dozen trees, not just any seed will do for the discriminating bird. It can differentiate between different seeds as it picks up each to test them for “soundness” by moving them up and down in its bill while quickly opening and closing its bill, in a motion known as ‘bill clicking’.
The Clark’s Nutcracker is not only well-designed to extract the seeds, but is also equipped to carry the seeds with a special pouch under its tongue. Its cousin, the Eurasian jay, shares this design feature, while other birds thought to be related, like the pinyon jay, have an expandable esophagus that they use to transport seeds.2,3 The nutcracker’s sublingual (below the tongue) pouch can accommodate up to 150 seeds at a time and increases to about the size of a walnut when it is fully loaded, thanks to its expandable nature.4
As with many other designs in nature, this pouch’s ability to expand is unlike anything human designers can imitate. Engineers would no doubt be thrilled to design materials with such flexibility, as there would be various applications, everything from water bottles to tanker trucks.
White bark pine in danger
Because these two species are so interconnected, the health of one impacts the other. The white bark pine is in jeopardy due to two threats: blister rust disease and the mountain pine beetle.5 Blister rust originated in Asia and is the deadliest disease for five-needle pines like the white bark pine. As of 2017, 28% of monitored trees in the Greater Yellowstone region are infected with the blister rust.6
A native insect, the mountain pine beetle has left its mark on the forests for many years, but never as negatively as the last several years. The female leaves a ‘J’ shape as she burrows under the bark to lay her eggs, which is a clear marker that the tree is compromised. Once they hatch, the larvae eat the tree from the inside. Especially hard winters can kill the larvae, but it only takes one summer for the beetles to kill a tree. The beetles have infected 95% of the backcountry portion of Rocky Mountain National Park.7 The combination of these two dangers resulted in well over half of the population of the Greater Yellowstone Ecosystem being labelled as having “high mortality”.1
A healthy stand of white bark has a positive impact on the environment in multiple ways. It delays the snowmelt with its upturned branches and shade which in turn helps prevent flooding in this semi-arid region. It also prevents erosion because its roots prevent soil loss, and it can withstand the high winds and steep slopes unlike other trees.
Additionally, it functions as a ‘nurse tree’ because it is the first to regrow following a fire and provides cover from the sun and wind to assist other seedlings like the Engelmann spruce and subalpine fir.1 Finally, it provides a quality food source for several additional species including bears and squirrels. The loss of this species would be devastating to the landscape.
In a good year of seed production, the white bark pine produces more seeds than are eaten, ensuring the next generation of seedlings. However, due to the increasing number of diseased and dying trees, there is concern that there may not be sufficient seeds to propagate the pine, let alone provide for the Clark’s Nutcracker and the 100+ other dependent species. One study showed that the white bark pine’s seed production had a direct impact on the nutcracker’s breeding behaviour. In 2011, 79% of the birds disappeared after a crop failure in 2010.1
In years of inferior cone production, the second choice for the Clark’s Nutcracker is the Douglas fir. These seeds are nutritionally inferior to those of the white bark pine, which are similar in calories per ounce to butter. In contrast, it takes 20 of the Douglas fir to equal one white bark pine’s seed.1
If humans were to do the same work spreading the seeds of the white bark pine, it would cost $2,500 per hectare.1 Because the birds are far more efficient and certainly more cost effective in replanting than humans, scientists are studying how to attract more Clark’s Nutcrackers to plant the seeds of those trees that are more resistant to the blister rust disease and the pine beetles.
The ‘cousin’ of the Clark’s Nutcracker, the Eurasian Jay, also has a reciprocal relationship with the European oak. It is credited with being the major propagator as it plants more than a thousand acorns annually. It is significant in replenishing the oak population which has decreased due to commercial development and loss of forest. These two bird species, along with other close relatives, are probably the same kind, i.e. descended from the same two birds that survived the Flood on Noah’s Ark.8
Masters of Memory
The Clark’s Nutcracker’s most important contribution is what the bird does with the extracted seeds. Once it selects the best seeds, the bird buries them 3 cm deep, the optimum depth for germination, in caches of up to 10 or so in an area covering up to 50 km2 (20 sq mi). This process is repeated over and over to store the seeds that sustain it through the long winters. In doing so, each bird can hide up to 100,000 seeds for the winter. Some contribute to communal caches as well as to private ones.1
These thousands upon thousands of seeds are buried and then covered by many feet of snow which remarkably does not impede their recovery. Under these extraordinary circumstances, these ‘bird-brains’ shine with a memory to be envied. These remarkable birds can recall the location of their seed caches, sometimes totalling 30,000 seeds or more, for up to 9 months!9 How often do we scavenge for our misplaced car keys or exit a store and cannot remember where we parked the car only a short time ago? We could only wish to have the capacity to remember details and locations like this exceptional bird. Imagine being able to remember the exact location of buried seeds 6–9 months ago! Such is the extraordinary spatial memory of the Clark’s Nutcracker.
Sometimes they use markers like rocks or the base of a nearby tree to help them indicate the cache. Interestingly, in the winter when it needs to remember these numerous locations, the bird’s brain will physically swell as it recalls the exact locations. It will later shrink back in size after the seeds are retrieved, returning to its ‘summer size’.10 Many schoolchildren will be able to relate to this phenomenon!
Their tremendous capacity to remember and retrieve all their stores sustains them through the harsh Rocky Mountain winters. In the process, they perform an invaluable service for one of the world’s greatest remaining natural ecosystems. How could these birds possibly evolve to such mental feats? Psalm 147:9 says, “He gives to the beasts their food, and to the young ravens that cry.”
References and notes
- Axelson, G., Soul Mates, Living Bird, allaboutbirds.org, 7 Oct 2015. Return to text.
- Bock, W. and 2 others, Morphology of the sublingual pouch and tongue musculature in the Clark’s nutcracker, The Auk 90:491–519, Jul 1973. Return to text.
- Balda, R. and Kamil, A., Linking Life Zones, Life History Traits, Ecology, and Spatial Cognition in Four Allopatric Southwestern Seed Caching Corvids; pigeon.psy.tufts.edu, 2006. Return to text.
- Clark’s Nutcracker Overview, All About Birds, Cornell Lab of Ornithology, accessed 30 Oct 2020. Return to text.
- Lanner, R.M. and AskNature Team, Pouch Stores Seed: Meat Bird, asknature.org, 29 Aug 1996. Return to text.
- Maloy, O.C., White pine blister rust, Plant Health Instructor, 2003; last updated 2018. Return to text.
- Forest Health: Mountain Pine Beetle, National Park Service, nps.gov, accessed 5 Nov 2020. Return to text.
- Eurasian Jay, wikipedia.org, accessed 17 Oct 2020. Return to text.
- Leonard, P. How Clark’s nutcrackers find buried seeds under a blanket of snow, allaboutbirds.org, 14 Apr 2016. Return to text.
- Bumann, G., How good is your memory? youtube.com, 4 Dec 2018. Return to text.