The Blue Jay (Cyanocitta cristata) is a familiar, large songbird known for its striking plumage and noisy calls. With its perky crest and a mix of blue, white, gray, and black feathers, the Blue Jay is easily recognizable. These intelligent birds exhibit complex social systems and strong family bonds, often mating for life. While often disliked for their perceived aggression, Blue Jays are fascinating creatures with a diverse diet and intriguing behaviors.
Breeding and Family Life
Blue Jays maintain tight family bonds. They often mate for life, remaining with their social mate throughout the year. Only the female incubates; her mate provides all her food during incubation. For the first 8-12 days after the nestlings hatch, the female broods them, and the male provides food for his mate and the nestlings. The female shares food gathering after this time, but the male continues to provide more food than the female. Some individual nestlings begin to wander as far as 15 feet from the nest 1-3 days before the brood fledges. Even when these birds beg loudly, parents may not feed them until they return to the nest; this is the stage at which many people find an “abandoned baby jay.” If it can be restored to or near the nest, the parents will resume feeding it. The brood usually leaves the nest together when they are 17-21 days old. When young jays leave the nest before then, it may be because of disturbance. The jays are usually farther than 75 feet from the nest by the end of the second day out of the nest. Young remain with and are fed by their parents for at least a month, and sometimes two months.
Communication and Mimicry
Blue Jays communicate with one another both vocally and with “body language,” using their crest. When incubating, feeding nestlings, or associating with mate, family, or flock mates, the crest is held down; the lower the crest, the lower the bird’s aggression level. Blue Jays have a wide variety of vocalizations, with an immense “vocabulary.” Blue Jays are also excellent mimics. Captive Blue Jays sometimes learn to imitate human speech and meowing cats. They will often copy the calls of hawks, especially the red-shouldered hawk.
Aggression and Dominance
Blue Jays are disliked by many people for their aggressive ways, but they are far less aggressive than many other species. In one Florida study, Red-bellied Woodpeckers, Red-headed Woodpeckers, Florida Scrub-Jays, Common Grackles, and gray squirrels strongly dominate Blue Jays at feeders, often preventing them from obtaining food, and Northern Bobwhites, Mourning Doves, White-winged Doves, Northern Mockingbirds, and Northern Cardinals occasionally dominated them as well. Sometimes Blue Jays mimic hawks when approaching feeders.
Food Storage and Dispersal
Blue Jays carry food in their throat and upper esophagus-an area often called a “gular pouch.” They may store 2-3 acorns in the pouch, another one in their mouth, and one more in the tip of the bill. In this way they can carry off 5 acorns at a time to store for later feeding. Six birds with radio transmitters each cached 3,000-5,000 acorns one autumn. Their fondness for acorns is credited with helping spread oak trees after the last glacial period. Blue jays assist with seed dispersal by hiding seeds and nuts for later use, and occasionally failing to retrieve them.
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Dietary Habits: An Omnivorous Approach
Blue Jays are omnivorous, meaning they consume both plant and animal matter. Their diet includes a wide variety of items, adapting to what is available in their environment. Studies have shown that the adult Blue Jay diet is about 88% vegetal. When I took care of injured and orphaned jays as a licensed rehabber, I found that they like a lot of variety in their diets, and seemed especially fond of some items, like ice cream, Froot Loops ®, canned dog food, cottage cheese, hardboiled eggs, walnuts, acorns, and peanuts. Back then, if someone had asked me what a Blue Jay’s favorite food of all was, I would have said strawberry ice cream, because the jays I cared for gobbled that down so very fast when it was offered.
Plant-Based Foods
A significant portion of the Blue Jay's diet consists of plant-based foods. Acorns are a particular favorite, and Blue Jays play a crucial role in dispersing oak trees.
- Acorns: Blue Jays are known for harvesting acorns and storing them in holes in the ground. They can carry multiple acorns at once, storing them in their gular pouch, mouth, and bill. These skilled jays can determine if the acorn is infested with pesky weevils-a process that still puzzles scientists-by simply picking one up in their beaks.
- Nuts and Seeds: Besides acorns, Blue Jays consume beechnuts, sunflower seeds, and other nuts. They will come to feeders for seeds. They pound on hard nuts or seeds with their bill to break them open.
- Fruits and Berries: Blue Jays also eat various berries, small fruits, and sometimes cultivated fruits.
- Grains: Grains are another component of their plant-based diet.
Animal-Based Foods
While plant matter makes up the majority of their diet, Blue Jays also consume a variety of animal-based foods.
- Insects: Insects, especially caterpillars, beetles, and grasshoppers, are a significant part of their diet.
- Spiders and Snails: These invertebrates also contribute to their nutritional intake.
- Eggs and Nestlings: Blue Jays are known to eat the eggs and sometimes even the baby birds of other species.
- Small Animals: Occasionally, they may consume small rodents, frogs, or carrion.
- Other: People have reported to me that their backyard jays are eating small birds killed at windows and roadsides, mealworms and other insects, dog food, sunflower seed, cracked corn, fruits on trees, acorns, and peanuts. In the past I’ve observed them feeding on road-killed carcasses, beechnuts, walnuts, peanut butter and peanut butter crackers, and eggs and baby birds-well, I haven’t seen adults eat these last two but I have seen them feed them to their babies.
Dietary Preferences and Variety
When I would feed Blue Jays, some days they’d go straight for one item and not another, while other days they might do the exact opposite. I think the way Blue Jays achieve a relatively balanced diet in nature is to select different items from day to day, quickly growing tired of one thing and moving on to others. Even though variety seems very important to jays, there were some food items that they hardly ever ate. I’d see them take corn but not peas, scoop out every trace of egg yolks while leaving the whites intact, and pick the raisins out of cereal while ignoring the bran.
Blue Jays and Acorns: A Symbiotic Relationship
Blue Jays play a vital role in the dispersal of oak trees. They harvest acorns and store them in the ground for later consumption. The acorns that are not eaten have the opportunity to germinate and grow into new oak trees. Because of this, Blue Jays are often credited with spreading oak tree populations after the last glacial period.
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Blue Jays in Northern Illinois
The blue jay is a large songbird that is common in Northern Illinois. A blue jay has a bright blue back with black markings, a white belly and a blue crest atop its head. Wings are blue with black and white bars across them. There is a collar of black feathers around the neck. It has a wide tail that is rounded at the end. Adult blue jays measure 10-12 inches (25-30 cm) with a wingspan of 13-17 inches (34-43 cm). The average adult blue jay weighs 2.5-3.5 oz (70-100 g). Breeding season occurs from March through July. Blue Jays form pair bonds which usually last until one member of the pair dies. They build nests in trees and shrubs. The female lays three to six eggs per clutch (group of eggs). Eggs are incubated for 17-18 days before hatching. The female primarily incubates the eggs, but males may assist with the incubation.
Conservation Status and Threats
Despite being common, conspicuous birds that have been studied by many researchers, much about Blue Jays remains a mystery. Although still common and very widespread in Massachusetts, the Breeding Bird Survey indicated that Blue Jays may be undergoing a quiet decline in abundance as a breeding species. Many Blue Jays do migrate a short distance in winter, but plenty are still around in the cold months. However, data from the Christmas Bird Count indicates that these overwintering birds are also gradually diminishing in number.
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