This study describes the morphology and investigates the possible function of the air bags found on the nestlings of Monteiro’s Hornbill Tockus monteiri. These air bags increased in size with age and mass of the nestling until 14 d of age, and then decreased in size. By 20 d of age, the air bags were absent. Histological examination of the air bags showed that they were integumentary structures composed of an outer epidermis and an inner dermis. The air bags were not connected to the respiratory system. The body temperature (Tb) of Monteiro’s Hornbill nestlings increased significantly with increasing age. Comparisons of ambient, nest and female body temperatures were made. Female Tb was higher than ambient and nest temperatures. It appears that airbags may provide an effective intermediate insulatory mechanism for the nestlings while they are developing their thermoregulatory ability. Therefore, it is suggested that the dorsal air bags evolved primarily for thermoregulatory benefits to nestlings, although further research is required.
Ostrich 2009, 80(1): 53–58