American Kestrels Rejecting Intestinal Tract of Prey

Several times I have photographed American Kestrels discarding the intestinal tract of their prey.  The prey has always been a vole or mouse when I’ve seen it happen, though it may occur with small birds also.  I was surprised by this behavior.  Every time I’ve seen it happen has been during our harsh winters when I would assume every last morsel of food would be significant for their survival.

Below is a series of photos where a female American Kestrel demonstrates the behavior with a vole kill.

Female kestrel begins to pull small intestine out of a vole

And deliberately drops it   

  The cecum? is discarded:  the intestine is still attached to the body and hanging down the side of the post

  She pulls more intestine out of the vole

  Breaks it loose from the body

  And deliberately drops it to the ground

  Finally, she pulls out the last of the small intestine, which she also dropped

I know of others who have seen similar behaviors in other raptors – a variety of hawks and Osprey.  Several theories to explain it have been mentioned by bird photographers and others who have seen my photographs.  Among them:

• “These organs are filled with potentially harmful bacteria”.  Then how are many raptors, owls for example, able to consume their prey whole without harmful effect?
• “These organs are filled with food of low value to the kestrel (vegetative matter). Why fill up on carbs when it’s protein you need?  Begs  the question – Would they also discard intestines of insectivorous birds?  I don’t know…
• “These organs would taste bad”  Perhaps, and that potential problem would be avoided for those raptors who swallow their prey whole.  However, I just can’t quite “swallow” this theory as I’m not ready to equate human tastes  with those of raptors.

I’ve never  seen a conclusive answer.

Up to this point I had never noticed kestrels rejecting the large intestine.  Then this past winter I observed and photographed this male doing exactly that.

Large intestine has been removed

And discarded

And finally, this is a female who has stripped the intestinal tract from the carcass except for one connection, then was spooked and flew off

Thanks for persevering through so many photos that some may find disturbing.  I’m fascinated with bird behaviors and this is one of the most interesting for me.  If anyone knows of a definitive explanation for this behavior I’d love to hear about it.

Ron