Avian Geophagy

Avian geophagy—In birds, geophagy (the intentional consumption of soil) is known for geese, parrots, cockatoos, pigeons, cracids, passeriforms, hornbills, & cassuaries. Brightsmith and Muñoz-Najar (2004) observed ten species of psittacids, three species of columbids, and two species of cracids consuming soil from banks of a river in Peru. They found that preferred soils were deficient in particles large enough to aid in the mechanical breakdown of food and help digestion. Percent clay content and cation exchange capacity (CEC), both predicted to correlate with adsorption of toxins, did not differ between used and unused sites as had been found in a similar study. Instead, preferred soils were more saline and had higher concentrations of exchangeable sodium. This suggests that the choice of soils at their study site was based primarily on sodium content. Experimental evidence has shown that soils are capable of adsorbing biologically relevant quantities of toxins in vitro and that soil consumption by parrots does reduce the absorption of toxins in vivo. Brightsmith and Muñoz-Najar (2004) did not find evidence that parrots choose soils with greater CEC or clay content, the characteristics that correlate with the capacity to adsorb toxins. Instead, they found that birds chose soils with higher concentrations of sodium. These two findings are not mutually exclusive but instead suggest that there may be a set of conditional rules for soil selection. In situations in which sodium concentrations are variable, the birds appear to choose soils that are highest in sodium (this study). In areas in which sodium concentrations are uniformly high, birds may choose the soils that have the largest ability to adsorb dietary toxins.

Article Source – www.biology.eku.edu/RITCHISO/birddigestion.html

Photo Source – www.pbs.org/wnet/nature/realmacaw/photoessay6.html

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