Wild Neighbors: CSI Cosumnes River

By Joe Eaton
Sunday January 09, 2011 - 07:36:00 PM
Victim: an American coot.
Gary Kramer, US Fish & Wildlife Service
Victim: an American coot.
Suspect: a female northern harrier.
Len Blumin
Suspect: a female northern harrier.

You’d think identifying a dead bird would not be much of a challenge. It helps if the deceased is intact, though. 

Ron and I got out of the house last Friday and drove up to the Delta—the Phil and Marilyn Isenberg Sandhill Crane Reserve, to be exact—to visit the wintering multitudes. It’s always good to see and hear sandhill cranes, even if in relatively low numbers. There were also a couple of large congregations of tundra swans, a variety of ducks, and a lot of red-tailed hawks, hanging around waiting for the tule fog to burn off. Redtails aren’t social birds, but we counted at least half a dozen in the same oak tree. 

We went on, as we usually do, to the Cosumnes River Preserve, a splendid multi-agency venture that includes old-growth riparian forest and nearby marshes. The preserve is also notable for its restrooms, which are few and far between in that part of the state. 

Across the road from the visitors’ center, a trail leads out into the marsh; paved at first, eventually turning into a boardwalk. It’s an excellent place to see cinnamon teal up close, and sometimes even the elusive Wilson’s snipe. 

In the middle of the paved part of the marsh trail were the remains of the aforementioned dead bird. Not just dead, but dismembered. Wings, spinal column, and legs had all been disassembled. At first, since the feet were gone, we thought it might have been a duck. Then we found the skull, neatly defleshed. The chicken-like beak pegged it as a coot. (Coot feet, unlike duck feet, have lobed as opposed to webbed toes.) About a foot away, nearer the water, there was a pile of black-to-dark-gray feathers, and a few white ones from the underside of the tail. This bird had been thoroughly plucked. 

But whodunit? We wondered about a peregrine falcon, a raptor that would be entirely capable of taking out a coot. But peregrines have a habit of leaving the wings of a carcass attached, through the breastbone. The size of the prey seemed ambitious for a red-tailed or red-shouldered hawk. Northern harrier seemed the most likely suspect. Although coot would be about at the upper limit of eligible prey for a harrier, we had seen it done. (Old Southern codger: “Do I believe in infant baptism? Hell, I’ve seen it done!”) A couple of years ago we watched a female harrier attack and drown a coot. She was unable to get airborne with it, and eventually lost her prize to an opportunistic redtail. 

One other possibility: there was a trace of something musky at the scene. We knew river otters frequented the marsh, having seen their spraints—the special term for otter droppings—on the viewing platforms. We knew otters prey on young waterfowl. “They eat the ducklings like they were popcorn shrimp,” a Fish and Game warden once told me. But the plucking and careful disarticulation was not an otter’s MO. A creature that swallows crayfish whole is not going to be finicky about feathers. Maybe an otter had investigated the scene, hoping for leftovers. 

I have neglected to mention that the remains were quite fresh. The whole thing happened in broad daylight, or at least foglight, at a location that gets a fair amount of foot traffic. Whatever killed the coot was a bold predator indeed. 

Back home, I went straight to the invaluable Birds of North America site. I quote from the entry on the feeding behavior of the northern harrier: “Large items, especially birds, are plucked and eaten, usually on the ground but sometimes on elevated perches. Smaller items swallowed whole. Small birds usually beheaded, bewinged, and befooted.” 

Not an airtight case, maybe, but I would still lean toward the harrier theory. That’s about as conclusive as forensic birding usually gets.