biology zoology blog benno meyer rochow strange taste for indigestibles

Strange Taste for Indigestibles

Strange taste amongst our feathered friends: Stories of food pellets

It is important for teachers to involve their pupils and when I reminded my wife, who was a high-school teacher in biology and geography at that time, that some birds swallow pebbles, elephant seals swallow stones as big as tennis balls and freshwater turtles are known to have gobbled up coins tossed into the water while marine turtles ingest plastic bags that clog up their intestines, it gave her an idea.

She was going to give her pupils some food pellets to analyse that a friend of ours had collected from underneath a tree in his garden. These grey boluses, measuring 1 – 2 centimetrs in width and 2 – 3 centimetres in length, contained bits of hair, recognizable feathers, tiny skulls and bones and what seemed pieces of eggshell and chitinous parts of insects. Obviously, an owl had been using the tree regularly to rest and to regurgitate the indigestible food items – hence the accumulation of such food pellets at the foot of the tree.

Owls are well known to bring up and spit out material their digestive system cannot process like the fur and the bones of small mammals (mice and voles come to mind) and that they rest during the day in their favourite trees to sleep and digest is also no great news. However, in one of the owl’s food pellets we examined, there was a small red plastic ring and that was certainly unusual. Or wasn’t it? It was hard to fathom how it could have got inside the owl, but what many people do not know is that not only owls, but many other birds as well, including kingfishers, seagulls, and crows to name but a few, produce food pellets. Even some snakes regurgitate the inedible material like, for instance, egg shells in case of the famous Indian egg-eating serpent Elachistodon westermanni or species of the African genus Dasypeltis.

Perhaps the strangest food pellets encountered in any bird have been reported from urban crows. In one location, favoured by flocks of these noisy and unpopular, but smart, city dwellers, food pellets were picked up and found to contain rubber bands, plastic rings, strips of aluminium foil, a wristwatch strap, pieces of string, chewing gum, and even putty. Most likely the birds swallowed these indigestible objects by accident and one would have expected them to learn from their mistakes and to have avoided these indigestible objects in the future.

But who knows, there may have been some fanciers of chewing gum or rubber bands or putty in the bird world and the uptake of items like these may not have been purely accidental. Small stones are equally indigestible, but numerous species of birds, especially seed eaters, swallow them for a purpose. Lacking “the real thing” (namely worms) our city dwellers may have found that rubber bands, even if they don’t taste like worms and do not provide any calories, are the nearest thing to worms one can get in the concrete world of our big cities and in this way have satisfied their needs. Only future careful observations, perhaps involving school pupils, can solve this riddle of the urban jungle and ourrubber band consuming city crows.

© Dr V.B. Meyer-Rochow and, 2019.
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