But Gilardi et al.10 found that soils preferred by parrots contain lower available quantities of most biologically significant minerals than non-preferred soils, and much lower quantities than the parrots' preferred plant foods. Hence, unless the parrots are making a big mistake in their taste preferences, they are not selecting soils for mineral content. A third function of geophagy, proposed for ungulate livestock, is to buffer the rumen contents6. Because parrots lack a rumen, it will come as no surprise that their preferred soils have no more buffering capacity than distilled water. Because many of these chemicals are positively charged in the acidic conditions found in the stomach, they bind to clay minerals bearing negatively charged cation-exchange sites2,3,5,9.
Peruvian parrots behave like sophisticated human tourists and hunter-gatherers.
In their capacity to bind quinine and tannic acid, the preferred soils surpass the pure mineral kaolinate and surpass or approach pure bentonite. Clearly, parrots would be well qualified for jobs as mining prospectors. Gilardi et al. confirmed this hypothesis with two sets of bioassays. Many of the brine shrimp died, confirming the toxicity of the parrots' diet. Second, Amazon parrots were given an oral dose of the alkaloid quinidine with or without preferred soil, and quinidine levels were measured in the parrots' blood for three hours as absorption took place from the gut.