Tuesday, April 17, 2012
Midnight madness in a heron nest
Transcript of today's For the Birds
Ever since the Cornell Lab of Ornithology put up a couple of video surveillance cameras in a Great Blue Heron nest, I’ve been spending a lot of time watching the birds and helping to moderate the chat room at www.allaboutbirds.com/cornellherons . It was great fun watching the birds fixing up and adding sticks to the nest they built in 2009, and courting and mating, especially because all this takes place on the nest itself. I even got to see the female lay all five of her eggs, which was amazing. Every morning I woke up excited to see what would happen next.
Then last week, when I was sound asleep and several people were in the chat room, something darted at the mother and got her up, squawking in a loud, strident vocalization we’d not heard before. Next time they could clearly see the bird, she was missing the long, flowing nuptial plumes on the back of her head, though no other feathers seemed to be missing and she didn’t appear to have any injuries. One person on the Cornell staff went through the archived recordings and clipped out the video and played it in slow motion, and we could clearly see that the attacker was a Great Horned Owl. The next night the owl was back again. This time while the female was squawking, the male answered her from a distance.
The female heron looked exhausted, stressed, and intimidated. Female Great Blue Herons usually have night duty on the nest, but the male started spending more time near the nest with her. And for two nights the owl did not return. Then Friday morning at about 2:20 am, the owl came back. This time both parents fought her off. Friday night, something alarmed them, but we couldn’t tell what. The male has now been spending time at the nest each night, and last night, Monday the 16th, he was on for at least 13 hours in a row.
It’s impossible to know what the Great Horned Owl wanted, but we’re certain she wasn’t after the eggs--owls can’t swallow large eggs and seldom if ever feed on small ones. She wasn’t after the nest itself. Great Horned Owls do take over old Great Blue Heron nests for their own breeding, but it’s too far into the owl’s own nesting for her to need a new nest. We don’t even know for sure that the owl is a female, but that’s my guess because females are more aggressive and attack larger prey than males. And Great Horned Owls are known to kill and feed on Great Blue Herons. The owls weigh 3 or 4 pounds while the herons weigh 5 to 7 pounds, so obviously an owl cannot carry one in flight, but can strip meat from a heron and carry chunks back to its own nest to feed its young.
Then yesterday, the 16th, we saw that one of the eggs is dented. It’s possible that during an owl attack as the mother crouched or jumped up, she pressed one egg against the stick nest too hard, or that one of the parents stepped on it at some point--we just don’t know.
Exciting as watching the cam has been for me, it’s been fraught. This is no population of birds for whom collecting data and observing mortality is a matter of scientific curiosity. People who have been watching these particular birds interacting and painstakingly turning their eggs and incubating for endless hours are invested in these particular birds. I wake up in trepidation, afraid to turn on my computer in case a tragedy took place over night. Birds devote 100 percent of their time and energy and focus on nesting, and we humans watching the cam are suddenly feeling what this investment really means.
Posted by Laura Erickson at 7:26 AM