Baby owlets are obligate carnivores: their digestive systems can only cope with meat, and it needs to be whole food with skin, bone and varying amounts of indigestible material such as fur, feather and scale.
Whole food provides the correct balance of calcium and phosphorus, which is critical for the growth and development of the musculo-skeletal system. These little birds are being fed a mix of food that will ensure they grow up big and strong.
In the wild, parents change the type of food given to babies at different stages of development (just like human parents!) If you find orphaned baby birds, it is very important to get them to a trained rehabilitator as quickly as possible to ensure that the correct food with the right balance of nutrients can be given