Intelligence in Nature - Jeremy Narby [62]
parrots choose fine-grained soils with high clay content and correspondingly high cation exchange capacity and presumably can adequately masticate hard food items with their powerful and dexterous bills. Hence, geophagy in parrots invites alternative hypotheses on its function based on the structure and potential function of the clay itselfâ (pp. 912â13). They add: âIn summary, analyses of geophagy soils and experiments on captive parrots strongly reject the grit and pH-buffering hypotheses, and although minerals are released, our data suggests that minerals are unlikely to be the primary cause of the geophagy in parrots. From the in vitro adsorption trials, the effects on the toxicity of parrot food items, and the reduction of bioavailability of [the harmless plant alkaloid] quindine in captive birds, we conclude that geophagy can function to detoxify dietary toxins for vertebrate herbivores. The persistence of clay in the gastrointestinal tract may also be an important function of geophagy. Since detoxification is likely to occur in the lumen of the gut and the gastrointestinal mucosa is roughly similar among vertebrates, these two functions, dietary detoxification and cytoprotection, may well be universally applicable to all soil-eating animals including humans, nonhuman primates, ungulates, and other herbivores. Because of their structures, however, soils can, and likely do perform a variety of functions for vertebrate consumers. Given the complexities of plant chemistry, gastrointestinal physiology, and animal ecology, the causes of this phenomenon are likely to be multifactorialâ (p. 918). Diamond (1999) comments: âPeruvian parrots behave like sophisticated human tourists and hunter-gatherers. Their preferred soils were found to have a much higher cation-exchange capacity than adjacent bands of rejected soilsâbecause they are rich in the minerals smectite, kaolin and mica. In their capacity to bind quinine and tannic acids, the preferred soils surpass the pure mineral kaolinate and surpass or approach pure bentonite. Clearly, parrots would be well qualified for jobs as mining prospectorsâ(p. 121). Engel (2002) writes about geophagy more broadly: âIf there is one fact on which scientists researching geophagy agree, it is that the phenomenon has many benefits. The director of the Geophagy Research Unit at York University, William Mahaney, concludes that all geophagy is a form of self-medication. And the consumption of soil is so widespread and so inextricably linked to wild health that Timothy Johns suggests that geophagy could be the earliest form of medicine. Although some soils can be a source of nutrients (minerals and/or trace elements), the primary benefit of clay consumption is in countering dietary toxins. In essence, eating earth allows animals to deal with the effects of unavoidable toxinsâ (pp. 69-70).
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P. 11: GLENN SHEPARDâS DREAM
See Shepard (1998).
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P. 14: FALSE ALARM CALLS BY BIRD SENTINELS
Munn (1986b) writes: âThe sentinel role has enabled T. schistogynus [the bluish-slate antshrike] and L. versicolor [the white-winged shrike-tanager] to establish a novel symbiotic relationship with other flock members. Both sentinel species rely on the insect-flushing abilities of other flock species for more than 85 percent of their food. Rarely do they steal arthropods directly from the bills of other birds. Rather, they sit in the center or beneath a group of actively foraging flock species and fly out or dive down after dropping arthropods flushed from hiding by the more active species. When a bird of another species begins to chase an arthropod that it has flushed out, the faster-flying, more aerobatic sentinel often catches the arthropod first. It is during these multi-bird aerial tumbles after arthropods that both species of sentinel give the same alarm call used when a hawk attacks or flies by. I interpret these calls as false alarm calls, presumably used by the sentinel to distract other birds and thereby to increase its own chance of capturing the arthropod. These aerial contests are over in less than