African Grey Parrots vary in weight, size and colour depending on their genetic background. Generally speaking, Timnehs are smaller and darker than Congos but Congos also show a variation in size and colour, originating as they do from a number of countries in Africa. The broadest range for all the Greys covers 275 grams to 650 grams (275 to 400 for Timnehs and 400 to 650 for Congos) with perhaps more typical weight ranges of 300 to 360 grams for Timnehs and 380 to 550 grams for Congos, but these are only guides and each Grey is unique. A baby African Grey will typically lose weight of 10 to 15% during fledging and weaning. A certain amount of fluctuation is normal after that, and the time of day can influence the weight, but a sustained weight loss can indicate illness so it is always a good idea to weigh even your adult Grey from time to time. In conjunction with weight the keel bone can also be felt to give an indication of "weight for build"; you should be able to feel the keel bone but it shouldn't be too prominent. You should be able to feel a good covering of muscle either side, convex rather than concave, but not so much that the keel bone is buried.