Ask the Biologist.
Q: While visiting Buffalo, NY, I was fortunate to be watching this red-tailed hawk when it coughed up a pellet. I knew owls did this, but didn't realize red-tailed hawks did as well.
Do all hawks do this?
ELIZABETH MARSHALL, RUSH
A: Neither hawks nor owls digest * everything they eat. They "cough-up" the indigestible parts as pellets, which are composed of feathers, fur and bones and sometimes invertebrate parts. The acid in hawk stomachs is stronger so there are fewer bones than in owl pellets. The pellets are "coughed up" or ejected prior to their next meal, usually one or two a day.
--SCOTT CROCOLL, DEC WILDLIFE BIOLOGIST