Blue Jays are beautiful blue birds perhaps best known for their aggressive and loud behavior. They are frequently seen stealing food from other birds, and protecting their own nest by attacking large predators. Their scientific name, "Cyanocitta cristata" means blue, chattering bird. Their calls sound like a "jay jay" or "queeble." They are also good at mimicking other bird's calls.
Blue Jays have dark gray legs and feet, light gray to white breast feathers, and a blue crest on top of their head. Their wings are blue with white and black lines crossing horizontally and a blue tail with black bars on top and white bars underneath. Their eyes, feet, and beak are black. They grow to be about 10-11 inches in length and 2.5 -3.5 ounces.  The crest on the top of their head is lowered or raised according to its mood. When it is excited or aggressive, its crest feathers stick straight up.  The male and female look identical except that the male is slightly larger. 
Their feathers aren't actually blue, it's the refraction of light. If the feathers were crushed, the blue hue would disappear. During the summer they shed all their feathers, most likely to stay cool during the summer heat. 
Mating usually starts in May and ends in late summer or early fall. A group of males will follow a female, bobbing their heads up and down, trying to show off. The female then chooses one of them to be her mate.  Afterwards, the chosen male will provide for her by finding food for her and getting suitable twigs for their future nest. 
They breed in gardens, farms, forests, or parks.  Their nests are built in trees or shrubs about 8-30 feet off the ground using twigs, bark, weeds, feathers, grass, roots, and whatever else they can find.  The inside of the nest is lined with mud and feathers and is about 10cm across. The total diameter of the nest is about 18cm.  They have also been known to have something white on the outside of the nest. It can be a candy wrapper, piece of bark, a paper towel they've found, or a white leaf. 
They are oviparous, meaning they lay eggs that hatch outside the body.  They lay about 3-7 blue-green eggs at a time, which is called a clutch of eggs.  They eggs can be a variety of glossy colors such as pink, blue, green, or olive with brown or purple speckles.  After the eggs are laid, they are incubated, mainly by the mother, for 18 days. The mothers shed the feathers off a part of their stomach called the incubation patch. The area is filled with small blood vessels and provides heat for the eggs or young fledges. 
After the eggs hatch, the young are helpless, vulnerable, and without feathers. After about 17 days they have all their feathers and at 21 days of age they are able to leave the nest. The baby birds are closely watched and fed by their parents until they leave their nest at about 2 to 4 months old. However, the fledglings can feed themselves at about 3 weeks old but still follow their parents around. 
 The young birds look identical to the adults except that they are lighter in color: their blue feathers are more gray and their black feathers are more brown.  They can start mating withing the first year of their birth. The average lifespan for living in the wild is about 17 years. 
The diet of a Blue Jay consists of nuts, fruits, insects, mice, frogs, and other bird's eggs.  To some people this may seem unacceptable, but it benefits the environment by keeping bird and insect populations from becoming too large.  They are omnivorous, meaning they eat both plants and animals. An estimated 24% of their diet is other animals, and 76% is organic matter.  They like to scare other animals into giving them their food and use their beaks to crack open nut shells.
They are known to be selfish and hostile. Blue Jays have been discovered chasing dogs, hawks, raccoons, and even humans away from their nests. Because of this, not a lot of people like to have feeders for them in their backyard. They are very aggressive and steal food from other birds.  Some have seen them stealing and eating eggs from others birds.  During winter periods, they tend to store up more food than they can eat, which can help the environment in the spreading of plant seeds. They have been thought to have aided in the spread of Oak Trees across North America.  However, they can also be a nuisance because they have been noted to carry the West Nile Virus. 
They are predated by hawks, raccoons, cats, snakes, squirrels, and falcons. Both parents will attempt to scare away any predator by chasing and attacking them.  Blue Jay families, consist of the young and its parents, but don't usually live in close contact with other families. The only time a large number of Blue Jays will gather is to scare away predators. They will even chase and attack humans if they come too close. 
Some have noticed that they use ants or ant excretions for preening (grooming the fur or feathers). This is called anting. There is a theory that they do this because something in the ant excretion helps soothe any possible irritation from the new feathers growing in. 
Most of them do not migrate, but stay in the same area all year round. They live in the Gulf Coast and Eastern United States all the way up to Southern Canada. They are slowly moving westward as well. They live more towards the edges of deciduous and coniferous forests or in urban areas such as city parks.  They love to reside in towns and cities where a quantity of large nut producing trees can be found.  In Missouri, they have estimated a 2% increase of Blue Jays every year.
The Blue Jay's scientific name is "cyanocitta cristata," which is a Greek and Latin word for a "blue, chattering bird."  Their call can be a "jay" sound or a "queedle" sound, along with the many other calls and voices they can mimic. 
They are very loud birds with many different calls. Their sounds can either be very harsh or more of a whistling sound. They are even known to imitate the calls of hawks, supposedly to warn other blue jays that a hawk is near. 
- Blue Jay The Central Pets Educational Foundation and its licensors, November 30, 2008.
- About the Blue Jay ScanSoft Trading Company Ltd., November 30, 2008.
- Blue Jay National Geographic Society, 1996-2008
- Blue Jay Shaw Creek Bird Supply, 2003
- Blue Jay Enchanted Learning, 1999-2008.
- Cyanocitta cristata Jake Frysinger, The Regents of the University of Michigan and its licensors,1995-2008.
- Blue Jay Habits Wild-Bird-Watching, 2007-2008.
- Blue Jay University of Minnesota Duluth, 1999-2008.
- Blue Jay All-Birds.com, 2003
- Blue Jay Cornell Lab of Ornithology,2003.
- Blue Jay Aspen Song™ Wild Bird Food, 2008.
- Oviparous Farlex Inc., 2008.