Many raptors regurgitate the indigestible parts of their prey, such as fur, scales and bones, and spit them out in fibrous balls known as pellets or casts. By examining the pellets 'contents, researchers can determine what the birds have eaten.
猛禽類常會把不易消化的食物，如小動物毛皮、鱗片、骨骼，像一團檳榔渣一樣吐出來，研究人員稱為食繭；由其中，可以求證黃魚鴞所吃的食物。