By midsummer, the nests are abandoned and the fledgling birds are on their own. I found this empty Robin's nest, while I was cleaning out my woodshed. I knew that there had been a family of Robins in the shed and I had avoided bothering them until they had gone.
The structure of the nest is admirable. Among the grasses and Red Cedar twigs that make up the majority of the nest, there are also pieces of garden twine and rope. This nest fledged two young ones.
Just two days ago. I saw a juvenile Robin investigating our blueberry bushes. It figured out how to get under the 'bird net' and pluck a berry for itself. I was impressed.
American Robin nest
Behind my house there are two mature Red Cedars, the scene of a little mystery. The larger of the two trees is 113 feet tall (35 meters).* As measured above the root swell at the base, the cedar is 16 feet in circumference and has a diameter of nearly five feet (1.5 meters). Though a tree this size would not impress the first settlers of Bellingham, who regularly encountered giants that were 15 feet across, in present day, it is an impressive. I estimate it is 80 to 100 years old, based on their tree rings usually being 0.5 to 1.0 centimeters thick. (* using a clinometer, which translates degrees elevation into tangents)
Red Cedar (Thuja plicata)
At the base of the tree I found the remains shown below.
You may have guessed from the nursery rhyme title that they are what is left of a Robin. This photo is of my original find, at the base of the south side of the trunk. All the 'evidence' seemed close together on the ground, next to a root. One feather was caught in a spider web above the ground. You see above, a clipped right wing, the upper and lower beak, an unattached tail feather, an unattached primary flight feather, a smashed skull with the feathers attached, and part of the leg (femur and fibula/tibiotarsus). The leg appears to have been eaten and later discarded or expelled. Who killed the 'Cock Robin'?
Later, I found the other clipped wing on the west side of the tree and feathers on the north and northeast side. This scattering is important in reconstructing 'who done it'.
Our neighborhood is well patrolled by cats, but this wasn't a cat kill. They leave a mangled, bloody mess, often accompanied by vomit. Besides, our friendly, neighbor cat has been concentrating on rodents and bringing them to me as a 'gift': 2 rats, 1 mouse, and a shrew in the last two weeks. This robin was neatly butchered after being caught. It was beheaded (and the brains eaten). It's wings were clipped, its larger feathers were plucked, and a leg was broken off. This was the meal of a raptor: either a Sharp-Shinned Hawk, a Cooper's Hawk, or a Merlin, which is a local falcon.
Who does the evidence point to? Both the hawks and the Merlin have tomial 'teeth', a sharp bump on their upper mandible, used for beheading prey. The clipped head does not point to one species over the other.
What about the position of the remains? It seems obvious that the 'food prep' was done from up in the cedar. The heavier pieces fell nearer the trunk and the lighter, free feathers drifted further away. Feathers and wings were found on different sides of this large trunk. A perch was used. This points away from the Sharp-Shinned Hawk for two reasons. First, "Sharp-shinned Hawks often sit on the ground where prey is plucked and then eaten." (Raptors of Western North American; Wheeler). Second, Robins are the upper size range of what a Sharp-shinned Hawk will catch. Larger females will catch a Robin, but not the smaller males. Sharpies are going to start migrating south, starting this month and may be starting upslope toward the Cascades now.
Cooper's Hawks are rare in my neighborhood, though they are occasionally found in the region. The fall migration starts soon for them (mid August) and they will be heading up the Cascades to catch the updrafts along the ridge lines. I don't think it is a Cooper's Hawk.
I do know that our subspecies of Merlin (Falco columbarius suckleyi) take their prey to well-concealed tree perches to pluck or 'plume' their food. They clip the head and eat the brain. They clip off the wings and tail and eat the legs/feet. I also know that where I live is well within the hunting range of our local Merlins. They usually eat smaller birds and insects (swallows, sparrows, dragonflies), but they have been known to eat Robins. Robins are at the upper limit of what they can catch and carry. The males form a resident population and the females migrate.
I cannot be sure who ate the Robin, but the clues explained above lead me to believe the hunter was Merlin. Investigating nature is often like this: putting together a circumstantial case from the available evidence.
