Spot-billed pelicans are relatively small pelicans. Mature pre-breeding spot-billed pelicans are generally gray dorsally, blending to white ventrally with a fairly long brownish gray crest. The eye-ring and most facial skin is an orange-yellow colour, though the skin in front of each eye is bright purple. The wings are grey with dark brown to black tips and dull white to slightly pink undersides. The bill is a pinkish to orange-yellow colour with large bluish black spots or smears on the sides and a dull purple pouch that is also blotched with bluish black. Pelicans in general are easily identified in the field by their unique bill pouch, which can stretch while fishing to hold almost three gallons of water in the larger pelican species. Spot-billed pelicans also have fully-webbed feet and legs of very dark brown to black skin. After breeding season ends, mature spot-billed pelicans lose some of the brilliance in their facial colouring, becoming more dull. The crest also diminishes in size. When newly hatched, spot-billed pelican nestling are initially naked with light skin, quickly growing a white down layer. As juveniles they develop a brown colour. Bill-spots begin to develop at approximately six months but are still indistinct until the moult into adult plumage begins in their third year. At this point, approximately 30 months of age, the identifying facial and bill marks become well defined. The change from brown juvenile to grey and white adult plumage is usually complete by autumn of the third year, just in time for the breeding season. Male spot-billed pelicans are slightly larger than females. The basal metabolic rate has not been investigated.