Squirrels, Acorns, and Tannins

  • Dietland Müller-Schwarze


Squirrels, but also birds such as jays, bury acorns in the ground to cache them as winter food. By this behavior, they also disperse the acorns and start the germination process by exposing the acorns to soil moisture. Burying protects acorns from surface-feeding competitors such as deer, ruffed grouse, and turkeys. It also prevents other squirrels from pilfering the stores, provided the “owner” remembers where he had buried the seeds, and other squirrels are not attracted by the odor of the buried seeds.

An acorn is technically a fruit, although customarily called a “seed.” It consists of a shell (pericarp) that encloses two seedling leaves (cotyledons) which in turn contain food reserves. The cotyledons connect to a tiny seedling by petioles. The seedling is also (technically incorrect) called the “embryo.” This embryo is located near the tip (distal end) of the acorn and is folded between the cotyledons. When germination starts, the pericarp splits at the tip. The seedling root (radicle) appears first. Then the entire seedling emerges, as the petioles of the cotyledons arch out downward and stretch to 2–5 cm. The radicle develops into a substantial taproot, while the presumptive leaves (epicotyl) and stem (hypocotyl) will grow little until spring.

Squirrels certainly do know their taxonomy: they identify acorns as either storable or less suited for underground storage. They bury red oak (Quercus rubra) acorns as winter caches, but eat immediately those of white oak, Q. alba (Smith and Follmer 1972; Smallwood and Peters 1986). White oak germinates already in fall, while red oak germinates later, and therefore “keeps better” in the ground. White oak sends a thickened taproot deep into the ground before winter starts. It thus “buries itself” and is thought to escape seed predation this way (Fox 1982). To prevent white oak acorns from germinating, gray squirrels kill these seeds by excising the seed “embryo” before caching them. Mature squirrels practice this technique more often than juveniles (Fox 1982). The squirrels discard the embryo.


Gray Squirrel Barley Grain Underground Storage Seedling Leave Squirrel Population 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


  1. Chung-MacCoubray AL (1993) Effects of tannins on protein digestibility and detoxification activity in gray squirrels (Sciurus carlinensis). MSc Thesis VPA & State University, Blaxcksburg, VAGoogle Scholar
  2. Dixon MD, Johnson WC, Adkisson CS (1997) Effects of caching on acorn tannin levels and blue jay dietary performance. Condor 99:756–764CrossRefGoogle Scholar
  3. Fox JF (1982) Adaptation of gray squirrel behavior to autumn germination by white oak acorns. Evolution 36:800–809CrossRefGoogle Scholar
  4. Howard WE, Marsh RE, Cole RE (1968) Food detection by deer mice using olfactory rather than visual cues. Anim Behav 16:13–17CrossRefPubMedGoogle Scholar
  5. Koenig WD (1991) The effects of tannins and lipids on digestion of acorns by acorn woodpeckers. Auk 108:79–88Google Scholar
  6. Moerman DE (1998) Native American ethnobotany. Timber Press, Portland, ORGoogle Scholar
  7. Müller-Schwarze D, Brashear H, Kinnel R, Hintz KA, Lioubomirov A, Skibo C (2001) Food processing by animals: Do beavers leach tree bark to improve palatability? J Chem Ecol 27:1011–1028CrossRefPubMedGoogle Scholar
  8. Schmidt KA, Brown JS, Morgan RA (1998) Plant defenses as complementary resources: a test with squirrels. Oikos 81:130–142CrossRefGoogle Scholar
  9. Smallwood PD, Peters WD (1986). Grey squirrel food preferences: The effects of tannin and fat concentration. Ecology 67:168–174CrossRefGoogle Scholar
  10. Steele MA, Knowles T, Bridle K, Simms EL (1993) Tannins and partial consumption of acorns: Implications for dispersal of oaks by seed predators. Am Midl Nat 130:229–238CrossRefGoogle Scholar
  11. Tomback DF (1980) How nutcrackers find their seed stores. Condor 82:10–19CrossRefGoogle Scholar
  12. Vander Wall S (1982) An experimental analysis of cache recovery in Clark’s nutcracker. Anim Behav 30:84–94CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • Dietland Müller-Schwarze
    • 1
  1. 1.College of Environmental Science and ForestryState University of New York-SyracuseSyracuseUSA

Personalised recommendations