Human bones have bone marrow, which is also one of the largest organs of the human body, with hematopoietic, immune and defense functions. So, is there marrow in the bones of birds?
In order to adapt to the life in the sky, the bones of birds have undergone great changes, which is to develop in the direction of “lightness” and “healing”. The bones of a bird account for only about 5% of its body weight, while human bones account for 20% of its body weight. The bones of birds are mostly hollow, with thin bone fragments, without bone marrow, filled with air, and there are oblique small bone beams inside, which can strengthen the weak bone fragments. In addition, the skeleton is integrated to reduce unnecessary movable joints, and the center of gravity is moved down, which plays a balancing role when flying.
However, in order to compensate for the inflexibility of the body (fewer joints), the necks of birds are particularly flexible and longer than other vertebrates. The swan has 25 cervical vertebrae, and the smallest hummingbird has 8 which is more than 7 for mammals.