Stop it. You’re making me hungry.

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.

Roth, T.C. II, and S.L. Lima.  2003.  Hunting behavior and diet of Cooper’s Hawks:  An urban view of the small-bird-in-winter paradigm.  Condor 105:  474-483.

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).

Bielefeldt, J., R.N. Rosenfield, and J.M. Papp.  1992.  Unfounded assumptions about diet of the Cooper’s Hawk.  Condor 94:  427-436.

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).

 

 

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About thomasbiology

I'm an Associate Professor of Biology at Queens University of Charlotte with a background in animal behavior with an emphasis in bird song. I've got two secret goals with this blog (well, since I'm sharing them, they're not so secret): 1. To encourage people to look at the natural world around them- not just as a hiking destination, but to notice all the little things moving around them all the time; and 2. To show some of the science that relates to these little things moving around. There's some really fascinating research out there that so few people get to see.
This entry was posted in birds, ecology, foraging, mammals, predation, raptors. Bookmark the permalink.

2 Responses to Stop it. You’re making me hungry.

  1. We saw a Cooper’s dive after a rat on our property. It was hanging onto one of those twirly corn things to lure 4-leggeds away from our bird feeders. (How the rat got there I don’t know, because we witnessed that it cannot get off without just dropping to the ground) I asked other birders about this because it seemed so odd. They told me that yes occasionally they rats and things, either because they are immature or if they see something available they will take it. I tell you this bumped up my rating of the Cooper’s ten-fold, as they preferred Juncos around our place and that’s our favourite bird.

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