Little Egret swallowing a prawn

William Ip photographed a Little Egret (Egretta garzetta) catching and swallowing a prawn head-first.

The prawn is covered with a continuous thin and flexible exoskeleton giving it protection without sacrificing mobility. This exoskeleton is periodically cast off through moulting as growth of the body proceeds. The new exoskeleton remains soft for some time before it hardens as calcium carbonate is deposited. As such, newly moulted prawns, as with other crustaceans are soft and vulnerable.

The prawn has no sharp spines as in fish. Instead, it has a sharply pointed rostrum that arises from the front end of the carapace, the tough covering of the head.

The Little Egret swallowing the prawn with the rostrum pointing inwards apparently causes no or minimum damage. And if the prawn has just moulted, there should be no possibility of injury. Once swallowed, the highly efficient digestive system would deal with the entire body except the exoskeleton. This would be compressed by the crop and eventually cast as a pellet.

Local photographers have recently documented pellet casting in owls, bee-eaters, shrike and kingfishers. However, so far, no one had photographed a heron casting a pellet, let alone observing one doing so.

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