Slings and Arrows: Why Birders Love to Hate Blue Jays
They're smart, spectacular, and vocally versatile, so is the species really so bad?
Indeed, as the story is told, a distinguished English bird man once visiting America was eager to see a living blue jay instead of a museum skin. He considered it to be the finest bird in the world and was surprised to find that it was quite ordinary.
While the blue jay is a year-round resident from southern Canada to the Gulf Coast and west to the far edge of the Great Plains, some of them migrate, though their numbers vary from year to year. For instance, as many as 154,000 southbound blue jays have been seen in one day from Hawk Tower at Holiday Beach Conservation Area on the north shore of Lake Erie. But as blue jay students Keith Tarvin and Glen Woolfenden note in their life history account for The Birds of North America project, "All aspects of blue jay migration [are] poorly understood."
Thoreau also portrayed the blue jay's characteristic cry as an "unrelenting steel-cold scream." Experts call it the "jeer call," and it's used for assembly and for mobbing predators (like my outdoor cats) and even human intruders. Or simply when a lonely jay wants contact with others of its kind. But blue jays have a remarkable vocal array, including what I consider one of the prettiest songs in the bird world. This is the "bell call," a series of clear, fluid whistles: kloo-loo-loo. Then we have the "whisper song," described by Tarvin and Woolfenden as a "soft, quiet conglomeration of clicks, chucks, whirrs, whines, liquid notes, and elements of other calls." Fledglings, they note, develop a full vocal repertoire by the time they are six months old.
The blue jay is also a near-perfect mimic of the calls of red-tailed, red-shouldered, and Cooper's hawks. The "hawk call" is typically heard when a jay is in an excited state, perhaps approaching a feeding station. One unproven theory is that jays are trying to trick other birds into believing a raptor is present. (Another black mark: deceit.)
While blue jays are common in woody towns and suburbs, they are truly forest birds. All kinds of forests--deciduous, coniferous, mixed. In fact, their distant ancestors are credited for the rapid northward expansion of oak, beech, and chestnut trees once the glaciers retreated 10,000 years ago. Trees, of course, are rooted in place. But as Louis Pitelka of the University of Maryland's Appalachian Laboratory wrote in American Scientist, "Populations of plants do move, infiltrating new territory by creep of root and shower of seed." And paleoecologists mapping ancient pollen data tell us that nut-bearing trees advanced as much as 380 yards a year, much faster than trees with windblown seeds, like maples and birches.
Simply put, blue jays airlifted the oaks, beeches, and chestnuts to new territories when the ice melted. Nut-squirreling mammals, experts point out, were of little help, since they usually hoard food close to the parent tree.
Curt Adkisson became hooked on blue jays when Carter Johnson, a plant ecologist formerly at Virginia Tech, mentioned seeing jays streaming along a woody fencerow in Wisconsin, carrying beechnuts from a patch of forest to a bog. This led to a three-year study in which the scientists calculated that resident jays made 13,000 round trips from their woodlot habitat to the swamp's vicinity over a 27-day period in September, dispersing 100,000 nuts to sites as far away as two and a half miles. The birds, they reported in American Midland Naturalist, carried anywhere from 3 to 14 beechnuts a trip. In our conversation, Adkisson, a private pilot, compared the sight of a heavily laden jay to a small plane laboring nose-high because of a weight and balance problem.
The fencerow route, the researchers noted, offered the slow-flying blue jays a place to hide from migrating hawks during the beechnut shuttle. And the birds were highly selective when collecting green nuts from burs in the tree canopy. They chose only sound, weevil-free seeds--seeds that were likely to germinate into beech seedlings if a particular bird died, forgot the location of its nut stash, or failed to empty the cache during a mild winter.
Meanwhile, back at Virginia Tech's Blacksburg campus, biologist Susan Darley-Hill was monitoring blue jay acorn dispersal from a stand of 11 pin oaks surrounded by a mosaic of residential neighborhoods, vacant lots, mature woodlands, and old fields. Jays, she related in the journal Oecologia, carried off 133,000 acorns, or 54 percent of the mast crop, while eating another 20 percent on the scene. Most of the nuts left beneath the trees were parasitized by insect larvae and worthless.
The foraging blue jays, she explained, held an acorn with their feet and hammered the nut's cap with a closed bill until it came loose. The birds then used their lower mandibles to pry the cap off and either hammered the acorn open and ate it or swallowed the nut whole for caching. The expandable throat and esophagus of a blue jay can hold up to five pin oak acorns or three larger ones from white oaks, and the bird typically collects one more nut in its bill before departing.
Arriving at its cache site, the blue jays usually regurgitated their acorn haul in a pile, then dropped the nuts one at a time within a few yards of each other, covering them with leaf litter. Darley-Hill reported that 91 percent of the caching sites in the Blacksburg study were on suburban tracts or bare soil where colonies of pin oak seedlings were already thriving. One cached acorn, she added, would never germinate. The jay stuffed it in ivy covering a brick wall.