POLITICS: THE SAD STORY OF WOLVES,
CONDITIONED TASTE AVERSION, AND THE WILDLIFE MANAGEMENT HIERARCHY.
( Revised October, 2010 )
Lowell K. Nicolaus
Is it “real”? Among humans, there is a universal but vague familiarity with the process of CTA. When reminded of the process, hardly any adult will fail to volunteer an occasion when a familiar and preferred food (or drink?) cannot now be consumed after having been once associated with illness. Anyone who has searched the subject of conditioned taste aversion (or, CTA; also referred to as the “Garcia effect”, conditioned flavor aversion, taste aversion conditioning and sometimes “aversive conditioning”) will have noticed that there is much available on the subject. A casual search reveals many web sites that describe work on CTA and a closer examination shows detailed discussions of CTA in basic psychology and animal behavior texts (1, 2, 3). A thorough search discloses a vast and very broad scientific literature reporting many thousands of research articles in which hundreds of scientists have described how it works and what effects it can have upon behavior of all animals (4). CTA has been produced in invertebrates as different as sea anemones and gastropods and in a bewildering variety of other animals, including humans (5, 6). 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.
The standard practices of shooting, poisoning or otherwise killing animal “pests” are not very selective, are increasingly resisted by the public, and have often failed to produce long-term reduction in depredation. For example, for more than a century coyotes have been extensively killed in the U.S. but both their range and their populations are actually expanding. Fences and other physical barriers are expensive, difficult to maintain and usually completely out of reach in poorer nations where the majority of endangered species exist and where subsistence agriculture makes every loss to wild animals much more acutely-felt than in developed nations. Repellents largely do not confer protection to prey unless they can be continually and perfectly applied to target prey. Frightening devices often become quickly ignored. Guard animals (dogs and llamas) seem, however, to deter small predators such as coyotes and the potential and the limits of their usefulness should be pursued.
Although there are some circumstances in which CTA is inapplicable, there 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.
The Fore Brain. This portion of the brain is not principally involved in the formation of Conditioned Taste Aversion. Since most people badly confuse the learning of CTA with the learning that occurs in the fore brain, we must dispose of it first to avoid this difficulty. The fore brain is composed of the outer cerebral cortex, where most of our conscious “being” is experienced, together with sub-cortical structures that contribute to the functioning of the cortex. Taken together, the fore brain is built to receive input from the external world and make decisions that guide the animal through its external environment. It uses routines enabling it to improve its performance through learning, and so we and other animals can change the way we respond to and “view” the world on this basis. In general, this learning is a process by which the brain sorts out irrelevant stimuli from relevant signals that are precise in space and time. The learning is rather like trial and error/success, since the external world has so much irrelevant noisiness in it. The rules it follows to “make sense” out of all the confusion through a process known as “classical conditioning” are as follows (18):
The Brain Stem. The unique and powerful features of CTA are understandable only if you understand the general functioning of the brain stem and how it regulates the internal melieu of the body. Among other things, the brain stem receives input concerning the internal working and condition of the body and makes executive “decisions” regulating that internal working. It controls such “vegetative” functions as movement of the gut to aid digestion, respiration, and constriction of blood vessels to fine-tune blood flow (3). Most people are surprised to hear that the brain stem, together with its associated structures, can also “learn” some things much better than the conscious forebrain. 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). This is where decisions concerning what foods you prefer to eat and what foods you prefer not to eat are made.
It is structured as follows (19): 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. Taste information from the medulla is brought forward to an area beneath the fore brain, and a little of this is allowed to reach the cortex where we can consciously report that we “taste” something. This information is very limited, however (we consciously taste only “sweet”, “sour”, “salt”, and “bitter”, often confusing sour with bitter). Most food flavor we experience consciously is really scent, not taste.
[We consciously know little about our unconscious selves, but we can make contact with our powerful unconscious “other person”. For example, consciously decide to hold your breath for as long as you possibly can and a very different inner person will soon oppose you. Or, you might consciously decide to jam your finger down your throat, or chew on an aspirin full of bitter alkaloid and you will soon see what your brain stem thinks of the idea. By doing the last two of these, you are also getting into contact with what it is like for an animal that is confronted with the taste of a food for which it has acquired a conditioned taste aversion!]
If the outcome of digestion and absorption is “good” (nutrient repletion), then all is well and this taste will be “remembered” by the brain stem as acceptable and so again be welcomed in the future. Since the food is still desirable, external cues associated with this food will continue to be sought by the animal as it forages in the external environment. That is, the unconscious brain stem decides what food the conscious fore brain “wants” to pursue. As they say, “You might be able to control what you do, but you can’t so easily control what you want to do!”
If the food is poisoned, then something very different happens. 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, which is also known as the “emetic center”. Sufficient stimulation here results in vomiting which purges the poison. Poisons that don’t irritate the gut may remain long enough to be absorbed into the blood. If so, then vomiting occurs when another small area in the brain stem near the NST called the area postrema (AP), is triggered by blood-borne poisons. 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.
What we now understand about the structure and functioning of the brain stem can, in theory, explain why CTA is so powerful and different from classical conditioning. Each of the unique characteristics of CTA listed above under What exactly is CTA? now makes more sense:
1. A delay in time between a meal and illness still produces CTA while such a delay would ordinarily prevent classical conditioning. Since this part of the brain only receives information concerning taste and internal condition of the body, there is little opportunity for confusing and competing information to interfere with making the connection between the remembered taste signal and illness that follows some time later.
2. Since taste and illness information converge at the important brain stem regions, there is a special link between taste events and illness events. This is why electric shock does not alter preference for food taste and bells and whistles don’t get avoided when they precede an illness (7, 20, 21).
3. 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.
4. Again, since the taste-illness axis is insulated from confusion, there is less interference that might result in the kind of “forgetting” associated with classical conditioning. The brain stem will grimly remember the taste of a food that was associated with illness for a very long time without any need to be “reminded” by reinforcement.
5. 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 taste to have access to the taste-illness system (8, 9, 10). Non-taste food cues don’t have access unless there is at least some taste cue present during feeding. Precisely how this process works is a matter of continuing research.
6. CTA only seems irrational if one only considers familiar, conscious learning and thinking processes. It makes much better sense once you understand that unconscious processes that “listen” only to the internal condition of the body decide food preference.
7. Since location and the particular circumstances surrounding a meal that
induces illness do not have access to the brain stem, memory of these details
is not retained by it. The food
taste (and scent/appearance) associated with illness will be avoided wherever
8. The remarkable similarity of behavior among such a wide variety of animals now makes sense, also. Of all of the parts of the central nervous system, the brain stem has evolved the least and so has remained similar among vertebrates. Structural similarity in the nervous system strongly suggests functional similarity.
In 1977, my students and I found that
free-ranging raccoons in a natural setting could be easily induced to cease
attacking and killing live chickens by consuming chicken carcasses laced with
small amounts of Lithium Chloride very well distributed in the baits (14).
The same individuals were observed before, during, and after eating
baits and since the only raccoons that attacked chickens after treatment were
those not present during the treatment, the results seemed clear-cut and
lasted as long as we continued the study (over a year).
Since then, research involving free-ranging predators has proceeded, but its rate has been slowed by lack of funding; a subject I will discuss briefly at the end. In all of the studies involving free-ranging predators the predators were entirely outside of captivity, entirely untouched and entirely free to move wherever they wished. In these field studies, baits were simply placed in the most conspicuous locations possible to optimize the chances that these free-ranging predators would find, consume them, and thus be treated. In much of this field research designed to produce and evaluate CTA among free-ranging predators, eggs were used as prey. This is because eggs are familiar and preferred prey of a very wide variety of predators and aversion-producing substances can be added to the interior. Eggs are also totally without their own defense against predation. Therefore, whether or not CTA can suppress predatory attack among free-ranging predators is a much more clear-cut event than would be the case if eggs were capable of escaping predation without the protection of CTA.
By randomly assigning breeding territories of predatory birds into treatment and control sites in 1981, we demonstrated that free-ranging American Crows very quickly acquired CTA by eating green-colored eggs treated with a small amount of well-mixed illness-inducing agent (26). This not only suppressed attack upon eggs of a particular color in places where their consumption produced illness, but also untainted eggs of the same color in other locations as well. All the while, Crows occupying other breeding territories consumed untreated eggs freely. I repeated the procedure in 1982 with Common Ravens that developed CTA to illness-causing eggs designed to look like those of Greater Sandhill Cranes in a national wildlife refuge (27). At the refuge, breeding pairs of Ravens defended their territory against intrusions by the many non-breeding Ravens. In effect, treated territorial Ravens that refused to consume the eggs themselves, “baby sat” the surrogate eggs by protecting them from predation by others that had not been treated. Again, Ravens in breeding territories assigned to the control group ate “Crane” eggs freely. CTA suppressed attack upon eggs among free-ranging American Crows in two further studies (28, 29) and among a wide variety of free-ranging mammalian egg predators as well (30, 31). In a modified replication of the old raccoon study, individually ear-tagged free-ranging raccoons were observed in the full sequence of consuming untreated egg prey, consuming treated eggs, and then returning to be observed to ultimately avoid untreated eggs at a distance during a post-test spanning two years (15). More recently, CTA has been established among free-ranging nuisance black bears (32) and among free-ranging black birds that consumed insecticide-tainted insect prey (33). On only one occasion in any of my studies have predators failed to acquire a long-term aversion that resulted in avoidance of untreated target prey. Mongooses in the Virgin Islands learned to discriminate between treated and untreated eggs because in the tropics treated eggs began to decompose within 2-3 hours and so both scent and taste of these eggs differed from that of untreated eggs (34).
Our working model. The working model we have always followed in predicting that a taste-illness pairing that produces CTA should suppress the killing of prey, wherever they are encountered, is based upon observations of encounters between prey and predators with CTA. Prey survive these encounters because predators with CTA respond to them with “disgust” rather than killing and eating them. 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). Free-ranging predators in field studies have been observed to respond in a similar manner on occasions when they have been observed to come into close contact with offending prey (14, 15, 32, 33). Predatory attack in field studies has generally been absolutely suppressed, presumably because both predators with CTA and their prey are free to avoid each other at greater distances than in captivity.
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.
CTA can control predatory behavior in so many different settings, why is it
not being used right now? I
have been asked this question many times.
My response has, until quite recently, been a shrugging “ask the
governmental agencies with the responsibility for wildlife management”.
In the process I know it sounds like I am hiding some flaw in CTA.
There is no hidden flaw. But,
the U.S. Fish and Wildlife Service, and now the U.S. Department of Agriculture
have widely pronounced that we have been in error and that CTA fails to
produce desired results. Before continuing, we must consider:
A word about scientific ethics.
Whenever a scientist believes that some other scientist has made
false or erroneous reports, it is his ethical duty to replicate the
questionable work in order to see whether or not the original reports are
justified before publicly announcing that the reports are false.
In fact, it is the scientific tradition that no new discovery ever
becomes widely accepted until it has been independently replicated many times
by other scientists and so undergone just this kind of careful scrutiny.
It is precisely for this reason that every rigorous scientific journal
demands that all reports it publishes include clear descriptions of the
methods used to produce results. Only
in this way can other scientists know how to replicate the results.
Claims made by the U.S. government that CTA failed to “work” were founded on tests of CTA that failed to replicate work reported by Gustavson and others. When the tests reporting “failures” of CTA were first published, it was our opinion that the reported results were perfectly reasonable…given the procedures that were used. The problem was these tests failed to replicate Gustavson’s studies. That is, in each case where it was possible to ascertain what the procedure was, the procedures differed from those Gustavson used and recommended. 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. Lithium Chloride tastes salty but live prey do not and so Gustavson recommended care in hiding a sufficient quantity of Lithium in the baits to induce illness in such a way that the taste and scent of baits did not differ from that of live prey. Captive or free-ranging predators that consume an illness inducing bait with food taste that differs greatly from that of live prey will discriminate between the two by avoiding the former and continuing attack and consumption of the latter. That is, an aversion to food item “A” does not dupe a predator into avoiding food item “B” if “A” and “B” differ in ways relevant to CTA. 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). Predictably, predators that consumed salty-tasting meat baits, refused to eat salty meat baits again after recovering from illness (showing that CTA had indeed been produced), but continued to attack and consume non-salty baits or live prey. In other “failed” studies, where substances other than Lithium Chloride were used, differences between bait and target prey continued to be included (38, 39), or the research was arranged in such a way as to make it literally impossible to produce a measurable CTA (reviewed in 35).
The flaws in the studies reporting “failures”
were fundamental, very easy to spot and were thoroughly critiqued in published
scientific review articles. To examine them, we have provided 3 articles to
view, Click on: Article 1,
Article 2, &
Article 3. But, to date no state or federal agency in the U.S. has published the
results of a legitimate replication of procedures used by Gustavson and others
to successfully produce CTA from as early as 1974. Instead, the flawed studies reporting “failed CTA”
continue to be used to support the claim that there is controversy concerning
whether or not CTA can “work”.
The only hopeful sign was in 1995 during a conference on repellents (42) where a paper was given supporting the use of baits that successfully mimicked live prey. Thus, our enjoiners to dupe predators by maintaining the same taste and scent cues between baits and live prey were finally adopted, but for some reason were repackaged under the unwieldy reference to “Conditioned food aversions based on deception or, CFABD. The author correctly made much of the need to be sure baits retained the same food cues as those of the live prey we wished to spare from predation. Curiously, however, none of the work in which this principle was so flagrantly violated was cited as obvious illustrations of why such “deception” was so necessary. The idea was near to the right track but unfortunately as seen below, this move, like all of our enjoiners, has not much influenced the leadership in the wildlife management hierarchy.
versus the American wildlife management hierarchy.
We really should not be too hard on government agencies with a
mission to manage natural and other resources. All resources are subject to
conflicting public interests and so it is rare that any action or policy
favorable to one interest will not injure the interests of others. Of
necessity, then, wildlife management agencies, originally claiming to be run
on the basis of the best scientific principles have long since entered and
remained in the sphere of politics. Those who rise to policy-making positions
in the bureaucracies are endowed with political skills and none rise who
oppose agency policy or their superiors. Agencies such as these tend to be
rigidly hierarchical and autocratic and retain a very long institutional
memory when they are opposed or their incompetence is revealed. Free inquiry,
the essence of science, is anathema to a bureaucracy since if it be science,
the outcome cannot be known beforehand and so free inquiry could well produce
information contrary to policy or make the past pronouncements of superiors
look foolish. That this almost never happens is the clearest evidence of what
is going on. In science, one attempts to find new facts. In government, the
science is too often assigned the task of finding facts to support policy.
How might Gustavson’s work be
replicated? Since 1974 public support for predator-prey research in which
predators kill and consume live prey has changed and so an absolutely pure
replication of Gustavson’s research is no longer possible.
A modified procedure, however, could still legitimately replicate
Gustavson’s procedure at least in so far as we currently understand the
process of CTA, complete with suppressed attack upon live prey and in a way
that meets any reasonable objection on humanitarian grounds.
Although a legitimate replication of Gustavson's research will require some funding, this sort of research need not be prohibitively expensive. CTA is a relatively low technology procedure that doesn’t require expensive bells and whistles. I know this because to date, I have had to pay for most of my research out of my own pocket and I am not a rich man (see the acknowledgements sections of each of the research papers I have authored).
I presume that once it becomes generally known what a proper application of CTA can do, the wildlife hierarchy will not be able to continue to resist it with the impunity they have enjoyed for so long. I believe the public deserves to receive what it pays for when it supports organizations responsible for wildlife research, though they will not receive it unless they are informed enough to demand it. This should be nothing less than honest and prompt reporting of results of good-quality, honest, aggressive research into any process with prospects of success, regardless of its bureaucratic popularity. Where research expertise outside of the organization exceeds that inside, it should be willing to support rather than resist these research efforts. Mistakes of the past should be admitted even though such admission might embarrass a colleague.
Finally. You are probably wondering why I am authoring this web page. I have to author it. Carl Gustavson died a few years ago, no one else has stepped in to correct an increasingly contaminated public record and there have been precious few competent scientists working on the problem of field applications of CTA. I am now semi-retired and so have nothing to gain other than peace of mind. From the first, CTA struck me as very interesting, and an honorable thing to spend my life researching. This I have tried to honorably do and I will no longer remain silent while it is so grossly misrepresented.
that every manner of objection will be raised by what is said here and fear
that the main point may become obscured.
Here then, is the main point: ordinary scientific ethics require a
legitimate and absolutely open public replication of research that has been
called into doubt, especially if the outcome is as important as the survival
of endangered species. I urge
that interested individuals and non-government organizations seriously
consider financially supporting legitimate replication of Gustavson's
work. If ever a little money could make a difference, this is
I expect to be crucified for speaking the truth but I fear being crucified for saying something stupid. I have therefore asked a variety of persons to read and comment upon these pages. These referees range from very wise laymen to loving well-informed family and eminent scientists. I would like to thank them all and would, under ordinary circumstances, do so by name. But, the cyber-ground we now tread is not firm enough to assure fair treatment to every contributor. Indeed, some have taken professional risks by participating. To the anonymous, I would like to express my sincere thanks. My relatives are already implicated and so I can name them with thanks and love: Jan my wife, John and Michael my sons, and Beth and Michelle my daughters. Thanks also to Lorraine and Brian Sinclaire and Torsten Langgemach for the German translation...And thanks also to Jose' Herrera for his help along the way.
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