are formed within six to ten hours of a meal in the bird's gizzard (muscular stomach).

Ornithologists may collect one species' pellets over time to analyze the seasonal variation in its eating habits. One advantage of collecting pellets is that it allows for the determination of diet without the killing and dissection of the bird. Pellets are found in different locations, depending on the species. In general, these are roosting and nesting sites: for most hawks and owls,