Oaks ‘n’ Folks – Volume 5, Issue 2 – November 1990
Introduction
Oak fanciers have long understood the importance of acorns as food for wildlife. But a closer look at the habits of some birds, particularly jays, shows that they do far more than harvest the acorn crop. An industrious group of jays can mount an acorn airlift that is nothing short of incredible, moving a forest worth of trees every autumn. Often the acorns are planted in the ideal spot for growing an oak seedling. Carter Johnson and Curtis Adkisson, in their article, Airlifting the Oaks, (Natural History 10/86:41-46) documented the oak planting abilities of eastern Blue Jays (Cyanocitta cristata). They discovered that 50 jays transported and cached 150,000 acorns in 28 days, about 110 acorns per day for each bird. I found two scrub jays(Aphelocoma coerulescens) in my backyard to be even more ambitious than their eastern cousins. They moved 140 acorns to their caching sites in just 75 minutes: that’s one every 28 seconds!
It’s understandable that the smartest bird of the suburbs would develop the urge to whisk away acorns. The acorn crop is a short-lived bonanza, arriving just before winter food shortages. Persistence and speed in acorn storage mean more meals of high energy carbohydrates later. You can speculate on whether this behavior is learned or innate, but the jays in my yard have no oaks within a mile of their home range. They removed acorns from a bench where I had placed them and hid them under shrubs and rocks about 10 to 15 yards from the bench, with no discernible pattern. Ornithologists believe that jays apparently know when they are under observation and scramble their behavior to confound research. I do know that they were not eating any of the acorns, even when they swallowed acorns so that more could be carried in flight and disgorged at the cache.
Unlike Acorn Woodpeckers (Melanerpes formicivorus) which store acorns at centrally located granaries, jays scatter their storage sites over a large area. Soft damp soils provide numerous locations and a quick means of covering the cache, so jays inadvertently put acorns where they are most likely to grow. Johnson and Adkisson found that seeds planted by jays had a higher rate of germination than seeds selected at random under trees, suggesting that jays select the acorns which are most likely to grow into seedlings. They point out that the goal of caching acorns may be food storage, but it provides a valuable means of dispersing and planting oaks. Further, they suggest that the rapid dispersal of oaks after the ice age resulted from the northern transport of acorns by birds.
Acorn production costs oak trees a great deal; however, the return in acorn transportation and planting by birds probably balances the energy lost. It is often difficult to describe the interdependencies of wildlife and plants, but there can be no doubt about the reciprocal benefits enjoyed by oaks and jays. UC researchers Mike Morrison and Bill Block suggest that the 300 wildlife species using oak woodlands provide many benefits in return, such as pest control and soil amendment. As we seek to restore and manage our oaks, it is important to remember the contribution of wildlife to the health and vigor of woodlands.
prepared and edited by John M. Harper, Richard B. Standiford, and John W. LeBlanc