by David Phalen
Birds have a unique system of storing calcium so that when they lay they will have enough to make egg shells. The long bones of the bird, particularly the femur and tibiotarsus, form what is called medullary bone prior to egg laying. Medullary bone forms on the inside of the
cortex and the calcium that is deposited there is put down in a way that will allow its quick mobilization. When a bird is about to lay, she will produce a precursor to yolk that will help to transport this calcium to the egg.
There is no doubt that some, perhaps most birds that are going to lay will increase their calcium intake prior to laying. This is especially common in budgerigars and cockatiels. This may be because they lay more eggs than they would in the wild with repeated clutching, or it may be because in the wild they would seek out higher calcium foods at this time and they are provided with a very high sources (cuttlebone and mineral block), so their instincts tell them to eat it.
It is clear that calcium reserves can be depleted in birds that continuously lay eggs, e. g., the single cockatiel or budgie. These birds will eventually develop egg binding due to weakness of the muscles of the oviduct.
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