What type of bird produces castings containing bones and sometimes entire skulls of prey?

Owls are unique among birds of prey in their method of digestion and how they process their food. They have a specialized digestive system that allows them to consume their prey whole, including bones, fur, and feathers. Because owls swallow their food entirely, they cannot digest everything. Consequently, undigested parts, such as bones and sometimes entire skulls of their prey, are formed into compact pellets known as castings.

These castings are regurgitated by owls after the bird has digested the metabolizable parts of the prey, such as muscles and organs. This behavior allows owls to efficiently handle their food intake, maximizing the nutrients they extract while disposing of indigestible remains. The presence of bones and skulls within these castings provides insight into the diet of the owl and the types of prey it hunts, making owls a subject of interest for both birdwatchers and researchers studying food webs in ecosystems.

In contrast, longwings, accipiters, and buteos have different feeding habits and do not produce castings containing undigested bones in the same way owls do. Longwings typically refer to a specific group of birds that may have agile flight but do not exhibit this casting behavior.