Shrike Feet
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Surely I’m not the only one to have grown up with the notion that shrikes impale their prey because their toes are too weak to hold it. This old chestnut persists, repeated even in BNA:
“[I]mpaling behavior represents a unique adaptation to the problem of eating large prey without benefit of the stronger feet and talons of raptors.”
I’ve been a skeptic ever since I saw my very first Northern Shrike, thirty or so years ago, carrying a hapless American Tree Sparrow in its feet. And today I saw another Northern, a first-winter bird, effortlessly hauling a Song Sparrow through the air–again, holding its prey clenched in its little talons as it flew 100 yards or so against the wind into a thicket.
Clearly, shrikes’ feet are plenty strong to hold even large and potentially squirmy edibles. So why do they impale their lunch?
It’s probably obvious to everybody but me. The shrike I watched this morning wedged his emberizid snack into the crotch of two branchlets, then hopped off to take a position beside the sparrow before plucking it. Aha. The masked bandit’s feet aren’t too weak: they’re too short, and probably set too far back on the body, for the bill to reach an object they hold.
No time to make a model laniid and experiment with the insertion point of the legs, delightful as that sounds, but I’m betting that I’m right. What do you think?
Can't remember ever seeing a Loggerhead Shrike carry prey in its feet, though.
6 Comments
November 29th, 2010 at 9:03 pm
Based on my own observations of (captive) Loggerhead Shrikes, I had seen them tearing and eating preying mantises between their feet without impaling them. I think tearing flesh from larger preys (small birds, reptiles, small mammals, etc) require more force than insects, i.e. they can’t step on it and tear at the same time.
One other explanation for impaling their preys is to create a cache tree, as well as to display their territory from the tree covered with impaled preys.
November 30th, 2010 at 7:30 am
[...] This post was mentioned on Twitter by Gunnar Engblom, Out walking the dog. Out walking the dog said: Crazy birds, shrikes. Shrikes can carry prey like hawks – why do they also impale? RT @Kolibrix BirdAz: http://bit.ly/dGWHfu [...]
December 2nd, 2010 at 5:46 am
Er, I am a bit confused here. In Germany (Europe?) it is “common knowledge” that shrikes impale their prey on thorns in bushes as a way to store extra food for rainy (unsuccessful) days – as PSYL mentions.
It never occured to me that this could have anything to do with the strength of their feet or length of their legs.
However, now that you mention it I might review this more critically.
December 2nd, 2010 at 11:43 am
We’re confusing two perceived phenomena: the one I was talking about was shrikes’ use of impaling (or wedging) while they eat their prey; the other is shrikes’ use of impaling when they leave their prey in a conspicuous position. As I understand it, the view that that latter impaling is simply to store food for later has largely given way to the belief that, as PSYL mentions, this behavior also has a “display” function.
PSYL’s observation of Loggerheads eating from between their feet is just the sort of counter-evidence I was hoping to hear: apparently they CAN reach between their legs to eat. Thanks, PSYL, and thanks, Jochen!
December 3rd, 2010 at 9:19 pm
I can’t believe people pay good money to go birding with you! Lol. . . .
December 3rd, 2010 at 9:21 pm
Money ain’t that good, Vince.
Don’t clutter my mailboxes any more, ok?
Thanks!