U.S. flag

An official website of the United States government


Main content area

Behavioral Strategies for Coping with Poisonous Plants

Pfister, J.A.
Bulletin 1999 no.70 pp. 45
feeding behavior, poisonous plants, toxicity, grazing, livestock, wild animals, poisoning, learning, mortality, conditioned behavior, metabolic detoxification, social facilitation, rangelands, ungulates, Western United States
Poisonous plants are an integral component of most rangelands in the western U.S. Although domestic livestock losses can be severe, obviously most wild and domestic animals grazing on rangelands do not die of toxic plant ingestion. Grazing animals use several interrelated behavioral and physiological strategies to reduce the risk of poisoning: (1) avoid or reduce toxin intake through changes in diet selection; (2) select a mixed diet and dilute the toxin; (3) consume a toxin in a cyclic or intermittent fashion; (4) eject a toxin once eaten; (5) complex, degrade, detoxify, and (6) tolerate the toxin once eaten. A central tenet of the first 3 strategies includes postingestive consequences and aversive conditioning, whereby animals learn from the negative or positive consequences of eating particular forages. The last 3 strategies describe how animals handle toxins once consumed. When livestock reject toxic plants in favor of less toxic or nontoxic species, learning is usually involved. Domestic livestock losses attest that learning is not a perfect avoidance mechanism. Nonetheless, learning enables most livestock to survive grazing on ranges with poisonous plants. Domestic livestock are more often harmed by toxic plants than are wild ungulates, probably because many livestock losses result from human management errors that override coping strategies. Furthermore, wildlife survival is probably enhanced by increased capacity to tolerate or detoxify toxins relative to livestock.