Zero for Two

By Bob Engel
Marlboro College Professor Emeritus of Biology and Environmental Science

I was trying to decide whether to feed the birds today.  If I could see some insects, so could my feathered buddies.  Who would want to beat on a black-oil sunflower achene to get the seed inside when insects were buzzing around?

sharp-shinned hawk eating it's prey

sharp-shinned hawk eating it's prey

But because I’m a softy, I had put out the feeder and was sitting on the porch watching a lot of nothing.  Maybe six or seven juncos were hunting on the ground nearby.  No chicks, titmice, or nuthatches, and no thieving red squirrels.  I started out into the yard to bring in the feeder.  And WHOOSH — for the second time in two days, the noise of wing and tail feathers controlling very sharp turns stopped me.  It was a male Sharp-shinned Hawk in full attack.  The juncos panicked and scattered.  They all made it to cover in the privet hedge.

Sharp-shinned Hawks are the smallest and most common species of the three species of so-called Accipiters — specialized, bird-eating hawks — that breed here.  All three species are built to chase birds, and all have relatively short, round wings and long tails.  Between the constantly beating wings and the long tail, they can turn on a dime and rigidly steer through those turns.  

The Sharp-shinned Hawk, Cooper’s Hawk, and Northern Goshawk all look pretty much alike, but they increase in size from about 11 inches, to 16 inches, and then to 21 inches.  The Goshawk, the largest is also a bit stockier.  The size of these bird eaters also determines what they attack.  

“Sharpies” are after typical little brown birds: chickadees, juncos, sparrows, maybe a nuthatch. Cooper’s Hawks take jays, woodpeckers, and maybe robins.  I saw one in Arizona that had eaten so much of its unlucky prey that the hawk’s crop stuck out as it a balloon had been inflated in the hawk’s crop.  A Goshawk hunts a little differently and takes some mammals in addition to larger birds.  A couple of years ago, I saw one perch in a big pine tree in front of our house.  It was a very pale gray bird, and, therefore a male.  He sat quietly.  Five minutes later, a Mourning Dove flew into the field and the sit-and-wait Goshawk leapt into pursuit.  He was immediately outflown by the dove.  The lesson?  If you’re a larger hawk that waits to surprise a bird, the prey has to be pretty slow, clueless, or maybe a grouse paying too much attention to berries.  

So back to my bird.  It was also a male (substantially smaller and with a brighter breast than a female), and because of its intense, focused attack, it had not seen me.  I froze and the hawk landed on a small branch maybe eight feet away.  He seemed to be composing himself…a bit of preening of some primary wing feathers, a little fussing with the scapularies (feathers at the shoulder) and some bill wiping.  Bill wiping shows up after all sorts of behavior, some of it aggressive, and seems to “redirect the mind.”  Off he went, and finally saw me at about three feet.  He had failed here and was going to try somewhere else (no sightings since).  At this point, I am not certain whether he was the same bird that our feeder birds, mostly chickadees, escaped yesterday.  Today, three chickadees perched near the hawk in the still naked tree and scolded him vigorously.  He looked up at them, and I was tempted to imagine that he considered the whole event degrading.  I would have.

Quite a few years ago, a couple of ornithologists published an interesting paper in the evolutionary and ecological journal American Naturalist.  Am. Nat., as it’s called by the cognoscenti, prints papers that include both some new data and a resulting, novel idea.  The authors looked at a variety of mammal-eating hawks like Red-tailed Hawks (they eat a few snakes, too) and the three bird-eaters we’ve talked about here.  The data they found (mostly in a variety of papers) showed that bird-eating hawks are much less successful per prey strike than are mostly mammal eaters or fish eaters.  

They mused that if food is hard to get, evolution might generate substantial size dimorphism amount the sexes of all three of the bird eaters.  Why?  Because they would hunt differently sized birds, thereby reducing competition within each accipiter species.  Among hawks and eagles, the Accipiter males are significantly smaller than the females. This is all interesting, but pretty theoretical.

What I had seen were two failed attacks by male “sharpies.”  How do you note a successful attack?  When you find a pile of feathers.  I have seen lots of feather piles, and I have seen lots of chases, but I have never seen an Accipiter actually catch its meal.