"Although at first many rejected the idea because it was so revolutionary, CTA is now probably supported by more solid empirical evidence than is any other behavioral process. With the sole exception of the wildlife management hierarchy in the United States, there is now no serious controversy within the scientific community concerning whether or not CTA exists as a unique and most powerful form of learning, or whether CTA can quickly produce long-term changes in predatory behavior."(2)

"When large predators are induced to approach humans because of associated foods, this threat could also be reduced by CTA without the need to kill the predator."(2)

"Although there are some circumstances in which CTA is inapplicable, threre are many others involving agricultural losses and declining populations of endangered species in which CTA may be the only solution. I believe efforts to reintroduce wolves and other carnivores into the wild in the face of opposition by agriculturalists are excellent examples of this."(3)

Characteristics of CTA:
"1. Illness is associated with food taste even with a substantial time interval between eating and illness onset.
2. Illness and food taste are linked by the way the nervous system is organized and so except as described in #5 below, animals do not learn to avoid non-food/non-taste things ar places in their external world through illness as a punishment.
3. Only a single taste-illness pairing may be sufficient to produce aversion.
4. The aversion is extremely resistant to forgetting, or extinction and does not require repeated illnesses for it to be remembered long after recovery from the initial illness.
5. As long as the taste of the food is present during the meal, other non-taste food cues such as food scent or, in the case of birds, visual food cues can be conditioned by illness, too. In this way, a taste-illness event results in avoidance of food from a distance on the basis of its scent or appearance (8,9,10).
6. … It has been observed that wolves and coyotes that have consumed a mutton bait containing an undetectable dose of illness-causing substance will, long after having recovered from the illness, avoid live, moving, bleating sheep as long as they taste and smell like the baits. This is so even though the bait was not living and moving when it was eaten (12,13).
7. Very different animals that have acquired CTA behave in remarkably similar ways, Mammals presented with the offending scent or taste close by may shake their heads from side-to side, wretch…..its appearance, the response may be much less dramatic; a simple act of ignoring an offending object. If they taste the food, however, they engage in just the same kind of head shaking and other behaviors seen among mammals (17).
8. Location and specific contexts are largely irrelevant to the formation and expression of CTA."

"the brain stem receives input concerning the internal working and condition of the body and makes executive ‘decisions’ regulating that internal working…. It is the brain stem, together with some structures that project above it, that ‘learns’ what foods are good to eat (that is, improve the internal environment) and what foods are dangerous (damage the internal environment: illness)."(5)

"The nerves in the tongue that bring taste sensation to the brain do not go to the conscious forebrain. Instead, they first go to a part of the brain stem in the medulla called the nucleus of the solitary tract (NST). Converging at the same place is a branch of one of these nerves (the vagus nerve) that also brings sensory impulses from the upper gut."(5)

"For predators, eating follows an inevitable sequence. It starts with food seeking (appetitive) foraging behavior controlled largely by the fore brain…. By the time food actually gets into the mouth the brain stem largely takes over (salivation and gastric secretion begin) and this includes taste sensation going to the brain stem. If the food has not been previously linked with illness, then the brain stem will allow it to remain in the mouth and be swallowed."(5)

"Many poisons produce gastric distress. These signals are brought by the vagus nerve from the gut to the nucleus of the solitary tract (NST) of the brain stem…. If the poison is removed by vomiting or by the lengthier and usually more punishing process of detoxification, then the animal may fully recover. The only lasting effect will be that a ‘memory’ for the taste of food eaten before the onset of the illness will be retained by the brain stem. As described earlier, other senses like food scent or appearance can also be conditioned and so the offending food may be avoided at a distance."(6)

"A delay in time between meal and illness still produces CTA while such a delay would ordinarily prevent classical conditioning…. Since taste and illness information converge at the important brain stem regions, there is a special link between taste events and illness events…. Since there is much less confusing ‘noise’ in the taste-illness system, only a single pairing of taste and illness may be sufficient for the learning to occur…. Animals that have experienced a taste-illness pairing can avoid the offending food/prey on the basis of non-taste stimuli (scent, visual cues) because in some way the taste component of the meal allows other non-taste cues that were simultaneously present with the atste to have access to the taste-illness system (8,9,10)…. The food taste (and scent/appearance) associated with illness will be avoided wherever encountered."(6-7)

CTA is not aversive conditioning: "Most aversive conditioning involves some form of external punishment such as electric shock or rubber bullets that are used to punish an animal just as it is engaging in some kind of forbidden behavior…. The learning follows the rules listed above for classical conditioning rather than the learning rules for CTA…. Since this learning is very different from CTA, it also fails to alter preference for food taste (7,18,20,21)."(7)

After wolves and coyotes were given tainted mutton baits by Gustavson, "Predatory attack was suppressed, resulting in the prey surviving unharmed over post-test durations vastly exceeding predator-prey confrontations in nature… CTA to control coyote predation upon sheep was again successfully tested in a 3-year field project in Saskatchewan (25)."(8)

"CTA has been established among free-ranging nuisance black bears (32)"(9)

"Long after having recovered from eating a treated sheep bait, captive wolves and coyotes gag and retreat as though punished again by the mere scent of live sheep (12,13)."(9)

"Sometimes, only the taste component is conditioned and so we find a hungry coyote whose nose and eyes say ‘YES!’ and so it attacks, but then whose tongue says ‘NO!’ What is seen then is the coyote with CTA to the taste of lamb wretch and run away upon biting lamb (12). When again confronted with live lamb, predator avoids at a distance."(9)

Many have attempted to replicate Gustavson’s experiments, but have failed because of significant procedural differences: "These differences usually took the form of including some feature of the experimental procedure that enabled predators to discriminate between the food cues associated with bait and those of the live prey…. Thus, while we recommended that meat baits be carefully constructed in order to hide 3.0-8.8 g of salty-tasting Lithium Chloride per Kg of meat bait (average: 4.0 g/Kg bait) (12,13,14,35), studies reporting failure of CTA used from 13.5-45.0 g Lithium Chloride per Kg bait (average 22.6 g/Kg bait, or a factor of 5.5 times more salty Lithium) (36,37)."(10)

"Fortunately, other substances such as thiabendizole and ethinyl estradiol that are very effective in producing CTA have been identified since 1974. They are much less detectable and they also do not produce severe illness symptoms among the predators (15,16,30,31,32,43)."(13)