Birds must develop rapidly with even the largest growing from hatchling to fledgeling in a matter of weeks. This Eurasian Eagle Owl (Bubo bubo) chick weighed 51 grams upon hatching on [10 March 2020]. Today, just two weeks later, it weighed in at over 400 grams!
Most of the resources utilized during the first stages of hatchling development are dedicated to the growth of down to assist in thermoregulation. Until a nestling is able to efficiently keep itself warm, one parent must continue to brood, or sit on top of the young chicks, constantly. This means that only one parent can actively hunt for food. In this series of images, you can see the transition from new, helpless hatchling to a 10 day old nestling covered in fluffy down.
