There are actually numerous birds of prey which cough up pellets and it is how they are able to process and dispose of the undigestable parts of their food. Despite what some people think, regurgitating pellets is not a sign of sickness but rather a healthy normal thing that these birds do on a regular basis. Owls are not the only birds that cough up pellets.
Some of the other birds which have been known to regurgitate pellets include eagles, harriers, falcons, kites, and hawks. These birds need a way of getting rid of certain parts of the animals which they eat that cannot be digested normally and as a result they come out as pellets.