Friday, January 8, 2010
Biodiversity Corner Blue Jay
Name: The Blue Jay is Cyanocitta cristata which translates roughly into a chattering blue bird with a crest. “Chattering” seems a much too generous-spirited description for the raucous bird I know, but it may be an attempt to accommodate the variety of sounds the Blue Jay can make, some of which we may not hear or may not attribute to the jay. I can’t quarrel with “crest” and am happy to accept “blue” even though the feathers have no blue pigment. The blue color comes from the way light is refracted from modified cells on the outer surface of the feather. If you hold a Blue Jay feather up to the light so it is back-lit it will be pale brown.
Family: Jays, including our Blue Jay, are part of the Corvidae family, which includes crows, ravens, and magpies. All members of the family are noisy birds, and all are known to mob owls and hawks.
Distinguishing characteristics: The Blue Jay is a familiar bird and easily identified. What may be less well known is that the black “necklace” varies a lot and may help Blue Jays recognize one another. Now that I know, I will attempt to distinguish the individuals that come to my yard.
Calls: The Blue Jay has a variety of calls and is also a mimic and a ventriloquist. In Bernd Heinrich’s new book Summer World, he tells of a group of 24 or more Blue Jays in March, perched in a treetop, bobbing up and down, and using six to eight different calls. The call we probably know best is the harsh loud “jaaay.” When I hear this call in the morning while I’m still in bed, it seems to translate into “Waaake up, you’re laaaate.” I much prefer the soporific soothing sounds of the Mourning Doves which tell me to “Roll over, sleep on.” Blue Jays use their mimicry skills to copy anything from squirrels to squeaky doors. In captivity, they can mimic human speech and learn to meow. In the wild, they frequently imitate raptor calls, especially those of the Red-shouldered Hawk. It is not clear whether this is meant as a warning to other jays that a hawk is present or if it is intended to fool other species into thinking a hawk is present, so they will depart from the scene, abandoning a food supply.
Food: The Blue Jay diet is largely vegetarian, made up of seeds, nuts, and grains. Acorns are a favorite food and are frequently stashed. One Blue Jay can carry up to five acorns at a time. Six birds tagged with radio transmitters each stashed between 3,000 and 5,000 acorns in a single season. About a quarter of the diet is from insects or small mammals already dead or injured. Blue Jays have a reputation for raiding the nests of other birds but in a study of stomach contents of 530 birds only six were found to have traces of eggs or hatchlings.
If you don’t like Blue Jays at your feeders, the Cornell Lab of Ornithology website suggests removing the feeder for a few days. The idea is that the birds will move away and find a new food source (at a neighbor’s feeder?) and stay with it until it is depleted or also removed. They prefer tray feeders to hanging feeders so you may be able to discourage them by using only hanging feeders.
The Massachusetts and New Hampshire Audubon Societies have several accounts from home owners of Blue Jays persistently pecking paint off houses and eating it. The reason seems to be that paint often contains calcium carbonate, and in the northeast both acid rain and the natural make-up of our soil result in calcium deficiencies which the birds are trying to correct. If you have this problem, you can stop the birds pecking your house by providing them with eggshells – cooked and crushed.
Bird Count Data: A trend line through the chart of Carlisle Blue Jay counts starting in 1973 would be almost flat, indicating no significant change in the population in 37 years. What is curious is the distinct change in the degree of fluctuation starting in 1987. Prior to that, the Blue Jays seemed to be in a four-year boom-or-bust cycle. For the past 22 years the population is more stable. It can’t be due to the West Nile virus (to which Blue Jays were very susceptible) because the earliest known incidence in the U.S. was in New York City in 1999. Factors that could be playing a role are cycles in the annual size of the acorn crop, migration behavior (which is not well understood), severity of weather during nesting season, stability of habitat, number of bird feeders, or something else. If you have an idea about this, send it in. (Thanks to Ken Harte for the Christmas Bird Count data and chart.)
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