Here is an excerpt from a very interesting article.
by Diane Porter
A blasting jeer comes from a blue jay in the big oak. Smaller birds scatter, except for a downy woodpecker, who freezes motionless on a tree trunk. A sharp-shinned hawk glides silently into my yard. It settles on a branch, watching for some small bird it can seize. It might have caught one, except that the blue jay ratted it out.
The blue jay may only have meant to warn other jays, but all the other birds understood perfectly. The feeders are suddenly bare, and the downy woodpecker thatwho did not fly holds so still that it’s almost invisible. I wonder if it’s even breathing. The sharpie won’t catch a bird this time.
Blue jays at sport
Walking in the woods on a winter afternoon, I hear a great ruckus of cawing in the distance, too high-pitched for crows. Coming to an opening, I see a crowd of blue jays in the air above the top of a bare tree. Jays are diving down into the branches, and others are springing up, as if the whole bird mass were at a fast boil.
I know what it means. The jays have discovered an owl in its day roost. A few feet below the top, an unfortunate barred owl hunches in the branches, eyes almost closed, as if trying to ignore its tormentors. Maybe my approach puts the owl over the top, for it breaks out of the tree and hurtles toward a thicket of oaks that are still clothed in dry leaves. The jays follow, a screaming blue streamer behind the brown owl, until it buries itself from view in the oaks. The jays don’t follow into the depths of the trees but perch on top, still cawing and yodeling, as if celebrating their team’s victory.
Family life and social structure
Even non-birders know a blue jay when they see one. It’s a bird found in backyards all over eastern North America. Yet, few ethologists have studied its social life, and most of blue jay society remains a mystery.
We do know that blue jays are monogamous. In early spring, the male feeds the female as part of courtship. In many cases, the bond is lifelong, but some blue jays find a new partner after one or several breeding seasons.