Jays and Oaks

Field Notes

~by Jim Eagleman

They fly in, loud and obnoxious, typically in groups of two to four, frightening all other birds at the feeder.

You are in for a show of dominance and aggression, not just with other birds, but often among themselves. “Thief, thief” is their call. It’s the blue jay.

Like other misaligned wildlife with bad reputations, the jay has a good side. Several, in fact.

It’s fall and you have probably noticed that the nut crop on oaks, walnuts, hickories, and beech trees is ripening. Collectively called the Mast, this annual production of nuts, along with seeds and fruits, is a giant pay-off for the wildlife that exploit them. This fall production will feed an assortment of forest wildlife through winter, including deer, turkey, many rodents, crows, and songbirds. The acorn crop alone is responsible for providing a food source for deer, making up as much as 75% of their winter diet.

Occasionally white oaks produce an oversized crop of acorns. It’s usually not just one oak here and there, but often in the same year nearly all the oaks in an entire region produce an extraordinary number of acorns. This is called masting and was thought to be an adaptation against acorn predation.

Acorns are a valuable source of winter food for many types of animals. If oak trees predictably produced a moderate number of acorns each year, the squirrels, deer, mice and jays, ducks, towhees, and all other creatures would surely increase their populations. These extra animals would outstrip the food supply and oak reproduction would plummet. But if oaks unpredictably produced many more acorns than the acorn feeders can consume, some acorns would escape the predatory scramble for food, and they would germinate.

When jays aren’t at your feeder, you may have seen them fly by with an acorn in their jowls. It’s almost comical. We know they can carry up to six acorns in the mouth—three on either side. Over eons, jays have become so dependent on acorns that they have adapted both physically and behaviorally to acorn shapes. The small hook on the pointed end of a jay’s beak, for example, is designed to rip open an acorn’s husk. The jay’s expanded esophagus (called a gular pouch) enables it to carry them off efficiently.

Just because a jay can carry more than one acorn at a time doesn’t mean they take them to the same place.

When birds cache groups of seeds for use during drought or cold, they bury them singly, just beneath the ground surface. These are at sites scattered throughout the winter territory, often over a mile from the tree. This makes jays the undisputed champions among acorn dispersers, competing with squirrels. It’s assumed each jay will remember all the places it buried an acorn and then know exactly where to go to retrieve it. But apparently this is more of a mental challenge than most jays are up to. And you can’t blame them. A single jay can gather and bury up to 4500 acorns each fall, and from research, it typically “remembers” where only a quarter of them are buried before springtime. If a Cooper’s hawk feeds on a jay in December, that jay retrieves none of its acorns. The end result is that each jay plants somewhere in the neighborhood of 3360 oak trees every year of its 7–17-year life span. Jays have enabled oaks to move about the earth faster than any other tree species.

Jays can help oaks in other ways, too. When oak disease hits an area, (sudden oak death and oak wilt are examples), there are survivors that may show a slight resistance. These hardy trees produce the most and best acorns. It is the jay that preferentially selects and disperses acorns with resistant genes. Future generations of oaks are likely to survive infections as seeds are spread throughout the countryside.

This is natural selection at its best, but it only works when a partnership between oaks and jays continues to thrive.

Here is another example of often overlooked relationships in nature: birds and trees, food and consumers of foods, seed dispersal and propagation—all taking place, all year long, all over our area, often on our own properties right here in Brown County.

A member of the crow family, jays are studied for their intelligence and cunning talents.

The jay isn’t actually blue. Blue is rare in nature. Pigments in the jay’s feathers (melanin) are brown, but we perceive them as blue due to a phenomenon known as light scattering. It is similar to the effects of a prism. The wings contain tiny pockets made of air and keratin, a substance like hair and fingernails. When light

hits these pockets, all the colors of the wavelength except blue are absorbed. The blue wavelength is refracted, which is what allows us to see the feathers as blue.

Known as “bully birds,” jays can be tolerated at your winter feeder if you give them space and a feeder of their own. Small feeders for chickadees, nuthatches, and woodpeckers that prevent larger birds from feeding can be installed. But the jay’s presence, the feeding and transport of oak acorns, and its cunning talents should remind us to welcome this visitor.

Look for jays this winter.