Do Blue Jays Plant Oak Trees? Acorn Caching Explained

How blue jays harvest acorns

In late summer and fall, blue jays visit oaks and beech trees and pick nuts straight from the branches. They carry them in an expandable pouch in the throat, and a jay can hold up to about five nuts at once: several in the throat pouch, one in the mouth and one in the tip of the bill.

The jay then flies off to a caching site, puts the nuts down and hides them. Each acorn is usually pushed into the soil or leaf litter and covered with leaves, grass or a small stone. Jays tend to bury acorns singly, a few meters apart, rather than in a large pile. This is called scatter-hoarding.

How many acorns does a blue jay bury?

A lot. A widely cited study in Blacksburg, Virginia, published in 1981, followed blue jays harvesting acorns from a stand of pin oaks. The results were striking:

Other research suggests that a single blue jay can cache several thousand acorns in one autumn. Many of the acorns that were left lying under the trees in the Virginia study were infested with weevil larvae, which suggests the jays were choosing sound, healthy nuts.

Why blue jays are such good tree planters

Not every animal that eats acorns helps oaks. Deer and many birds simply digest them. Blue jays help because of a combination of habits:

• They bury the nuts. Covering an acorn protects it from drying out and from many seed-eaters, which improves its chances of germinating.
• They carry them far. Gray squirrels usually bury nuts within a short distance of the tree. Blue jays regularly move them hundreds of meters to more than a kilometer, into new areas.
• They pick open ground. In the Virginia study, most caching sites were in suburban areas whose open, disturbed vegetation resembled forest edges and clearings, the kind of sunny sites where young oaks grow well. Oak seedlings were found growing at jay caching sites.
• They choose good nuts. Selecting healthy acorns means the seeds they bury are more likely to be able to sprout.

The jays preferred small to medium-sized nuts, such as pin oak, willow oak, black oak and American beech, which fit easily in the throat pouch. They avoided the large acorns of northern red oak and white oak.

Did blue jays spread oaks after the Ice Age?

During the last ice age, glaciers covered much of northern North America, and oaks survived far to the south. When the ice retreated, beginning around 20,000 years ago, oak and beech forests spread northward much faster than seems possible if heavy acorns simply fell and rolled from trees.

In 1989, ecologists W. C. Johnson and T. Webb argued that blue jays could explain this puzzle. Jays carrying acorns a kilometer or more at a time, year after year, could move oaks and beeches north quickly. It is not possible to prove exactly what happened thousands of years ago, but the idea is widely accepted as a likely part of the story.

Do blue jays remember where they hid them?

Blue jays belong to the crow family, which includes some of the best memorizers among birds. They use landmarks to relocate many of their caches during winter and early spring, when other food is scarce.

They do not recover them all. Some jays die over the winter, some caches are stolen by squirrels or other jays, and in years with plenty of food some acorns are simply never needed. Those leftover acorns are the ones that grow into trees. Unlike their relative Clark’s nutcracker, which is known to recover a high share of its pine-seed caches, the exact recovery rate for blue jays in the wild is not well known.

Squirrels and other jays as tree planters

Blue jays are not the only animals that plant oaks. Eastern gray squirrels also scatter-hoard acorns, and many of their buried nuts sprout too, as explained in do squirrels remember buried nuts?. However, squirrels tend to keep their caches close to the parent tree, while jays move seeds over longer distances.

In Europe, the Eurasian jay plays the same role for English oak and sessile oak, burying thousands of acorns each autumn. Foresters have long noticed young oaks springing up in fields and clearings far from any oak tree, and jays are a major reason. In the mountains of western North America, Clark’s nutcracker and the pinyon jay depend on pine seeds and help whitebark and pinyon pines spread.

Why it matters

Oaks are some of the most important trees in North American and European forests. They support huge numbers of insects, birds and mammals, and their acorns are a key food for wildlife. By moving and burying acorns, blue jays help oak woodlands regrow after fires, logging or farming, and spread into new areas as the climate changes.

So while a blue jay never sets out to plant a tree, its winter food stores add up to a quiet, long-term service to the forests of eastern North America.