Twice in the last week a large owl has made nighttime attacks on the incubating Great Blue Heron at the nest outside our office. The female heron does not seem to have been injured by the attacks, which included strikes by the owl very close to the bird’s head.
The attacks were caught by our live-streaming nest camera, and we’ve put together the clips into a short video. The nest camera is very sensitive to low light levels, but even so the views of the attacking bird are brief and blurry. The large bird appears out of the blackness, approaching from below the nest and flying at full speed. It aims at the heron’s head and its momentum carries it almost into the camera. At about 1:35 in the video you can briefly see the owl perch on a branch beyond the nest.
We’re drawn to nest cameras for the intimate views they give us into the activities of the parents and the fragile new lives of their young. The uninterrupted observation is also a source of new data, particularly in the case of hard-to-study species such as Great Blue Herons. But these owl attacks are also a reminder that life as a bird is fraught with uncertainty and danger. Even North America’s largest heron is not entirely safe from predators.
What’s even more interesting than the owl’s brief appearance is the female heron’s defense. Before the attack, she rests quietly over her eggs, feathers sleeked down, her head resting against her body with her long neck folded underneath her. As soon as the owl appears she jumps to her full height, spreads her wings, and lets out a long series of grating screeches. As the seconds tick by, she settles back over the eggs in an entirely different posture—feathers fluffed, plumes erected, her neck extended, fully alert with her heavy bill at the ready. With her wings she forms a tent over the nest and makes herself look as large as possible.
Based on the size of the attacker, the habitat, and the time of night, we believe this was a Great Horned Owl. The diet of these large owls is typically about 90 percent mammals, according to Birds of North America Online. Although they hunt birds relatively rarely, the tactic of taking incubating birds from their nests at night is a fairly common one—Great Horned Owls have been recorded taking coots, ducks, loons, mergansers, and grebes in this way.
Great Horned Owls also sometimes take nestlings at night, meaning that there may be some danger of an owl attack later in the nesting season. For now, the attacks seem to have subsided—the last one was on Monday night. We will continue to watch the herons and hope for the best.