Sacred Kingfisher regurgitates a pellet

A broad range of bird species regurgitate pellets. The following extract from Wikipedia explains regurgitation of pellets:

A pellet, in ornithology, is the mass of undigested parts of a bird's food that some bird species occasionally regurgitate. The contents of a bird's pellet depend on its diet, but can include the exoskeletons of insects, indigestible plant matter, bones, fur, feathers, bills, claws, and teeth. In falconry, the pellet is called a casting.

The passing of pellets allows a bird to remove indigestible material from its proventriculus, or glandular stomach.

The sequence of photos below shows a Sacred Kingfisher with a small crab meal, but before it swallows the crab it regurgitates a pellet. Given the large number of crabs in this bird’s diet I imagine expelling the indigestible parts of the crabs, especially the exoskeleton, is more comfortable than passing them through the digestive tract and exiting the back end. (1)

Please click on photos to enlarge. 

Sacred Kingfisher with a small crab.

The bird seemed to be taking its time to swallow the crab. Its throat was enlarged.

And then, to my surprise, a brown mass appeared with the crab still held near the bill tip.

Previous photo cropped to reveal a closer look at the pellet which appears to contain small fragments of crab shell.

Then the pellet was dropped and in a flash the crab was swallowed.

The bird looks relaxed and satisfied with the pellet expelled and the crab consumed. 

Many birds regurgitate pellets. Raptors and owls readily come to mind. I have seen Woodswallows regurgitating the hard shells of insects. Wikipedia lists some other birds that produce pellets: 

Many other species produce pellets, including grebes, herons, cormorants, gulls, terns, kingfishers, crows, jays, dippers, shrikes, swallows, and most shorebirds.

There are three other reasons some birds regurgitate. One is to feed young. For example parrots and pigeons regurgitate pre-digested seed to feed their young. Many sea birds feed their young by regurgitating food gathered over long distances and time periods. For example pelicans, albatross and shearwaters. This is also a good way of avoiding or reducing theft of food for their young from pirate birds such a frigatebirds, skuas and gulls. 

The second reason birds may regurgitate is due to disease - sick birds may expel food from their stomachs. 

The third reason is in response to stress, perhaps to reduce weight to enhance their flight from attack or to vomit food onto an attacker in an effort to fend off the aggressor.

(1) Note the photos were taken on the Brunswick River in northern NSW. There were good numbers of Sacred Kingfishers in this area which contained river margins, tidal flats, mangroves and an ocean beach.  There were plenty of crabs which we saw the Sacred Kingfishers hunting on a number of occasions.