Friday, May 1, 2015

Why do Parrots Eat Clay?

Geophagy, or the practice of eating earth-like substances (most notably clay) is not exactly an uncommon occurrence in the animal kingdom. Many ground dwelling/foraging birds that feed on hard grains and seed, for example, some doves and various species of fowls, may intentionally ingest small bits of pebbles and earth that aid in digestion. This is thought to be because these kinds of birds swallow their food whole and the small pebbles and rocks provide rough and hard surfaces to help mechanically break the food particles down in the crop - a digestive pouch located along the bird's neck. But not all birds ingest earth matter as a digestive aid. 

A modest flock of green-winged macaws (ara chloropterus) gather at a clay-lick in Peru
On the banks of the Peruvian Amazon River, and like clockwork each day, large flocks of parrots - sometimes numbering in the hundreds - gather to imbibe on clay rich soil. The gathering of so many parrot species in one location, is arguably one of the most unique and beautiful displays of group feeding in the animal kingdom. This behavior is practiced by many of the Amazon Rainforest's colorful collection of birds, most notably the larger and strikingly colored macaws. For the longest time, however, experts were baffled as to why the parrots were behaving in such a manner. Parrots, unlike other birds, have beaks that are perfectly adapted for chewing and do not as a general rule, swallow the nuts, seeds, and plant matter they eat whole. Earth matter, in other words, was not being ingested to aid in the digestive processes of parrots.

Pionus parrots flocking to a clay lick in Peru
An early explanation for geophagy in parrots was suggested by James Gilardi of the World Parrot Trust in 1996. Gilardi speculated that because parrots such as macaws frequently feed on a large amount of fruit, nuts, leaves, and other parts of the plants in their environment, they would in turn, inadvertently ingest a significant amount of plant matter that was poisonous, or caustic enough to cause substantive harm to the bird's digestive tract. It was therefore proposed, that in order to counteract the ingestion of these poisons, parrots would then later feed on large amounts of clay from the Amazon basin. The clay, in turn, was thought to have a binding effect on the poisons, neutralizing them, or separating them from the edible plant matter in the bird's digestive tract so as to not be absorbed into the body. The behavior was thought to be hardwired into the genetics of parrots who feed on poisonous plant matter as the birds were observed to visit these "clay licks" with such regularity and frequency, except in situations when weather conditions were unfavorable. For the better part of the past decade, this was the only explanation for geophagy in parrots and was thus largely accepted as a scientific fact by ornithologists all over the world. 

In an even more recent study, however, it is revealed that geophagy in parrots may in fact be utilized for yet another purpose and that is to counteract a supposed sodium deficiency in the parrot's living environment. The study was conducted by Donald Brightsmith of the Tambopata Research Center in Peru, who discovered that they key difference in the composition of soil ingested by parrots, and soil from the same bank that was ignored, was in fact not the soil's capacity for absorbing toxins (cation-exchange capacity) but rather, that soil favored by parrots was higher in sodium than others. This theory was also supported by the fact that the distribution of clay licks on the Western side of the Amazon basis seems to place many of these birds' habitats the furthest away from any oceanic influences and thus, away from the largest naturally occuring body of diluted sodium. A third theory was offered that parrots were thought to ingest clay to absorb trace amounts of vitamin B12 and calcium but this claim was largely unsupported as macaws residing outside of the Western Amazon region do not exhibit geophagy and so, the wild birds must be getting the bulk of their calcium and B12 requirements from another source. 


In captivity, it is largely accepted that macaws do not need to be fed clay. Companion macaws do not forage and are fed by their parronts thus reducing any or most risk of accidentally ingesting poisonous plant matter. Furthermore, all captive parrots should be fed a mix of parrot-formulated pellets, seeds, fruits, vegetables, and the occasional treat from the dining table that should ensure that almost all of their nutritional requirements are being met. 

photo source: wikimedia.commons.

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