Blue Jay

The pigment actually present in a blue jay's feathers is melanin, which is brown to black. The blue you see is produced physically, not chemically. Each feather barb has a spongy layer of keratin full of microscopic air pockets, and that structure scatters incoming light in a way that sends blue wavelengths back to your eye while other wavelengths pass through and are absorbed by the melanin behind. Because the colour depends on the intact structure, it disappears if the structure is destroyed; grind up a blue jay feather and the powder is grey-brown. The same structural mechanism produces the blue of bluebirds, indigo buntings, and a peacock's neck, and it is why those birds can look duller or brighter depending on the angle of the light.

In effect, yes, though not on purpose. In autumn a blue jay gathers acorns, tests them, rejects rotten or weevil-infested ones, and flies off to bury the good ones one by one in soil and leaf litter, often hundreds of metres from the parent tree and frequently at woodland edges and in open ground where an oak seedling can get light. The jay relies on remembering and eating these caches through winter, but it makes far more than it needs and forgets or dies before recovering many, and those buried, well-spaced, viable acorns are ideally placed to germinate. Studies of pollen and tree spread since the last glaciation credit jays, along with squirrels, with much of the rapid northward march of oaks across North America and Europe.

Blue jays are excellent vocal mimics and regularly reproduce the calls of hawks, especially the red-shouldered hawk, so precisely that experienced birders are fooled. There are two main ideas about why. One is deception — a jay arriving at a crowded feeder or a food source gives the hawk scream, the smaller birds scatter, and the jay has the food to itself. The other is information gathering — by imitating a hawk and listening for a real one to answer, or watching how other birds react, the jay checks whether a predator is actually in the area before committing to feed in the open. Both may be true at different times.

Their reputation as ruthless nest robbers is overstated. Blue jays do sometimes take the eggs and nestlings of other birds, and they will mob and harass birds and mammals near their own nest, but detailed studies of what blue jays actually eat find that animal matter, and nest contents in particular, make up only a small fraction of the diet, which is dominated by acorns, nuts, seeds, fruit, and insects. On balance blue jays are far more important as seed dispersers and as noisy sentinels that alert the whole woodland to hawks, owls, cats, and snakes than they are as a threat to other birds.