The Blue Jay (Cyanocitta cristata) returns to Evanston.

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The Blue Jay (Cyanocitta cristata) is back, after its population was decimated by West Nile Virus beginning in 2001. Calling “jay, jay, jay,” these birds are flying in loose “neighborhood” flocks just above the treetops. Bold, boisterous, mischievous, aggressive, elegant are some epithets applied to the species. “Rogues and thieves,” proclaimed John J. Audubon.  Although Blue Jays have been kept as pets (Audubon had one) and researched in the laboratory, much of their life history is poorly understood.  
Originally restricted to the United States east of the Great Plains and adjacent Canadian provinces, they have been extending into the northwest.  Jays and their relatives – crows, ravens and magpies – are lumped together in a family called “corvids,” the largest of our perching songbirds.  Humans consider corvids among the most intelligent of birds because of their range of learned behavior and adaptability,.  
Male and female Blue Jays look alike, although the male is slightly larger than the female. A bold black necklace separates the white chin and head from the grayish-white belly and grayish back. White wing bars on blue are distinctive. Bright blue tail feathers are striped in black and edged in white.  
Regardless of their name and appearance, Blue Jays are not blue.  A tail feather shed by a jay, when held up to the light, reveals only pale brown, the pigment of melanin. The blue color is the result of “light scattering,” the reflection of blue light from tiny transparent barbs on the feathers.
Many observers, including Audubon, have witnessed Blue Jays raiding nests for eggs and nestlings.  According to the Cornell Lab of Ornithology, however, when the stomachs of Blue Jays were examined in the lab, only 6 of 560 contained the remains of birds.  Their diet includes approximately 72 percent nuts, usually acorns and beechnuts, the remainder being seeds, grains, fruits, small vertebrates and insects.
Blue Jays often cache their food. They are capable of transporting a dozen nuts of varying types in one trip, filling the gular pouches in their upper esophagus with some, carrying another in the mouth and another in the tip of the bill.  They bury each separately, either by drumming a hole or covering it with leaves.  Cornell Lab reports “six birds with radio transmitters each cached 3,000-5,000 acorns one autumn.”
Blue Jays do not always recover their cached treasures. Research has shown that Blue Jays are more effective than squirrels in dispensing acorns, carrying them much farther from the parent tree and caching them in open habitats conducive to oak growth.  Blue Jays have been credited with spreading oaks after the last glaciation.  This behavior has given hope to scientists that in the event of global warming, Blue Jays will continue to spread oaks, the dominant trees of the eastern forest.
The Blue Jay in a yard on a summer might not be the same Blue Jay who stayed all winter.  Some birds stay put throughout one season, then migrate the next. An early 1960s multi-year study of Blue Jay spring migration in Madison, Wis. found Blue Jays, who are weak fliers, being carried on the winds, flying north, flying south, spiraling upward in the sky, hesitating before crossing a lake, flying singly and in flocks. The investigator, A.W. Shorger, finally concluded that “Jays in migration will not do what is reasonably expected of them.”
Scientists speculate that Blue jays are monogamous. They are not territorial but will fiercely defend their nests against any predators, particularly humans, cats and squirrels.
In contrast to their typical raucous behavior, a nesting pair is quiet.  In my northwest Evanston yard, a pair worked cooperatively on a nest in a Bradford Pear tree. The male provided most of the building material, while the female formed the nest. The male collected stick after stick from the ground or mightily wrenched a small live branch from a tree. Bark and leaves were added to the mix. Rootlets lined the interior. A light-colored rag was loosely woven in.  Spotted blue-green eggs were laid, probably four to five. Throughout the incubation period of about 17 days, the female rarely left the nest and was fed by the male, who also fed the nestlings.  When two nestlings fledged after about two and a half weeks, male and female both fed the young. The family stayed together over one heartwarming month.  The following year, the jays returned to the same pear tree. There, systematically, they dismantled the nest, stick by stick, and transported the entire collection, rag and all, it to an unknown location.
Blue Jays produce an astonishing array of sounds. They are well-known for mimicry, particularly of hawks. Mark Twain caught the temper of the species in “What Stumped the Blue Jays”:
 “There’s more to a bluejay than any other creature. He has got more moods, and more different kinds of feelings than other creatures; and mind you, whatever a bluejay feels, he can put into language. And no mere commonplace language, either, but rattling, out-and-out book talk – and bristling with metaphor, too – just bristling! And as for command of language – why you never see a bluejay get stuck for a word. … You may call a jay a bird. Well, so he is, in a measure – because he’s got feathers on him, and don’t belong to no church, perhaps; but otherwise he is just as much a human as you be.”
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