nestling period. In the chicks’ first few days after hatching, their sparse down is snowy white. The chicks subsequently undergo two basic moults before entering adulthood. The first moult usually begins after four days, in which black semi-plumes on the head and neck begin to emerge; followed shortly by the emergence of greyish-black down feathers over the body after one week of age. Some white down feathers initially remain attached to give a temporary mottled black and white appearance before finally receding to leave a darkish grey downy plumage. During development of the dark down, the bill, legs and feet are shiny black. A pale yellow stripe extends up the venter, the gular pouch is bright orange, and the iris is dark brown. At hatching, nestlings weigh 76-90g. After the chicks pass their third week of age, the black down develops olive streaks and the only parts of the body that do not appear dark are the bright orange gular skin and a small patch of white down above and below the tail. Just over 10 days later, black flight feathers develop, shortly followed by black contour feathers. At this point, the chicks are fledged and have their first full juvenile plumage after about a month of hatching. Hence, juveniles remain black at fledging, by which time the orange of the gular pouch has also turned pale scarlet. In the second moult, white down begins to return when the chicks are seven weeks old, followed by white semi-plumes then white contour feathers. The first white basic plumage is complete after three months and resembles that of adults. By this time, the legs and feet are now an incipient pink and the bill has become bicoloured (pale blue and maroon). Although the young now resemble adults, the skin surrounding the eye remains black for about a year before turning red, and the dark brown iris does not begin to yellow until after two years old. These are two potentially useful features that identify juvenile maguari storks; but in the field, the dark iris of the juveniles is the most reliable feature that distinguishes them from adults. Two hypotheses have been proposed to explain the dark colouration in the juveniles. First, the blackish feathers may serve as camouflage against both ground and aerial predators. Alternatively, the black plumage may serve a thermoregulatory function by enhancing its absorption of the sun's radiation. This