Yesterday, I was walking down Selwyn and came to a stop in the middle of the sidewalk. There, down someone’s gravel driveway, was a Cooper’s Hawk staring at me and eating something that it had pinned under its talons. I stood there for several minutes watching the bird alternate between watching me and taking those kind of stringy bites where it pulls apart the thing that it is eating. It is, at this point, that a typical urban birder gets viewed with suspicion, too. A woman walked by me on the sidewalk while I stood there, staring. She didn’t pause- in fact, I think she actually sped up to walk past the strange guy staring at rocks in a driveway. Ah well. She didn’t call the police, so I’m ONLY weird, not dangerous and that’s a good thing.
Anyway, back to the meat of the story. Really, back to the meat. I tried to see what the bird was eating, but I couldn’t tell much about it, except that it was definitely not a bird. Not a bird? But Cooper’s Hawks are sort of the idealized avian predator, known for hunting small bird prey. Is this an unfounded assumption?
One group of researchers looked at Cooper’s Hawks in winter and found that 100% of their diet was made up of birds. Actually, even more importantly, 95% of their diet was made up of just a few species: European Starlings (yay!), Rock Doves (pigeons) and Mourning Doves. The 4th most common species in the diet was the House Sparrow.
Now, the only issue with this particular work and the bird that I watched (which was clearly not eating a bird) is that this particular research took place in Indiana in the winter. We’re getting on in the season here, but we’re definitely not at a comparable time of year. Terre Haute in the midwinter is not likely to have many mammalian options as prey, especially not small mammals.
Another article, this one from the breeding season, did present some interesting findings. They looked at Cooper’s Hawks nests. Historically, people studied feeding at nests by looking at remains of the prey, but these researchers realized that this methodology actually biased the data. By using direct observations of nests- seeing what food was actually brought to a nest, these researchers showed that nearly 60% of the biomass of food brought to a nest was mammalian. What does this mean? It means that the view of Cooper’s Hawks as a bird specialist is…well…misguided. They certainly are good at taking avian prey, but they also invest a fair bit of time in eating small mammals (especially chipmunks at the sites in this study).
So, what was my bird eating? I never did find out. After a couple minutes of the stare-down, the bird finally picked up what remained of the carcass and flew off into the bushes. It looked smaller than a chipmunk, a mouse or a vole, maybe, but I can’t say for sure. Either way, it was a good meal for the bird and encouraged me to go home and make dinner (though a very different meal for me).