Use of activated charcoal and other particulate substances as feed additives to suppress bird feeding

Abstract

Osmotic strength is a function of particle number. The experiments described here were designed to test whether the consumption of a large number of small particles might induce strong osmotic effects that, in turn, could induce food avoidance learning. The experiments also evaluated whether the abrasiveness of fine particulates or their ability to act as organic adsorbants could mediate or contribute to the avoidance of adulterated diets. In experiment 1, captive European starlings (Sturnus vulgaris) were given two-cup tests between plain chow and chow adulterated with activated charcoal or Anjan-activaid, a product containing large amounts of activated charcoal. Both adulterants decreased consumption of chow at concentrations ranging from 0.63% to 5.0% (w/w). In experiment 2, starlings were given two-cup tests between plain chow and chow adulterated with quartz sand. At the conclusion of the experiment, the gastrointestinal tracts of test birds and other (control) birds were examined for lesions consistent with abrasion. Quartz sand decreased feeding at concentrations of 5.0 and 2.5%, but no evidence of lesions or inflammation was observed. In experiment 3, activated charcoal, Anjan-activaid, quartz sand, and calcium sulfate were placed in dialysis tubing and the tubes were immersed in water to test for differences in osmotic strength: no differences were found. In experiment 4, starlings were given plain chow and feed adulterated with calcium sulfate to test whether organic adsorption might contribute to repellency; unlike activated charcoal, Anjan-activaid, or sand, calcium sulfate is a poor organic adsorbent. No food avoidance was observed, consistent with the hypothesis that adsorbance was important for the effects observed in experiments 1 and 2. Although caution is necessary when extrapolating from the laboratory to the field, these results have testable practical implications: for example, activated charcoal or Anjan-activaid might be used as bird-repellent livestock feed additives and either of these substances or quartz sand might be useful as bird-repellent additives to landfill covers or as repellents applied to crops.