Ready for a rousing game of “Who Cast that Pellet?” Take a guess with this first pellet:
See the bone fragments poking through this pellet? Theo the Great Horned Owl left this after eating a furry white rat. His stomach muscles and juices broke down the meat, allowing the meal to continue into the intestines. But indigestible fur and bones remained in the stomach where they were pressed together and, eventually, coughed back up. The time required for this process depends on the size of the meal: larger meals take a longer time to process.
This pellet has smoother edges and no visible bones. If I split this pellet open, we would only find fur. Carson the Red-tailed Hawk ate the same meal as Theo, but hawk stomach acid is much more acidic and can disintegrate bone. The bones of her rat passed through, but the tough fur was still cast back up as a pellet.
While owl pellet schedules depend on when and how much they eat, hawks adhere to a circadian rhythm. In one study, Red-tailed Hawks cast a pellet at the first light of the day regardless of when they were fed the day before. They are even known to cast a pellet after a fast day with no food in their system. Their routine pellet casting at dawn may reflect their hunting strategy. Hawks require daylight to hunt, so emptying their stomach in the morning will prepare them for a fresh meal. Owls, on the other hand, can hunt during day or night, so their system simply empties after the food has been digested.
Learn more about raptor pellets in this Raptor Physiology chapter.