3D reconstruction of high-resolution, micro-computer tomography (CT) scans of thigh bones (femora) from Japanese quail (Coturnix japonica). Whole quail femora (far left and far right) from a male (left) and female (right) are visible here, together with corresponding longitudinal cross-sections (inner two bones) revealing the bone marrow cavity. Intact male and female femora appear almost identical; however the cross-sections reveal an astonishing quantity of medullary bone that is stored by the female quail for eggshell formation. Average length of an intact quail femur is approximately 40 mm.
Like many other birds, quails control the timing of their reproduction through a physiological process called photoperiodism. Quails are highly sensitive to day length and use this information to ensure that reproduction occurs during the most favourable season for their offspring (i.e. in the summer). Increase in day length results in a series of hormonal changes leading to greater oestrogen production and fertility. In birds, these hormonal changes also result in the formation of extensive "medullary bone" within the marrow cavity. This medullary bone is essential to supply the large amount of calcium required to form the eggshell.