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Learning in Rhinoceros Iguanas, Monitors and Other Lizards – observations on zoo animals

Rhinoceros Iguana

Observant lizard keepers cannot fail to become aware of the surprising degree of intelligence exhibited by many species. In the course of my long career at the Bronx Zoo, I was fortunate to have been able to observe the learning abilities of a number of species not often available in the pet trade.

Although species and individuals varied markedly in their capacities, one constant seemed to be that all recognized and responded to changes in their normal routine. This makes sense, of course, from the viewpoint of survival, but I was none-the-less always impressed by the rapidity at which most learned.

Rhinoceros iguanas, Cyclura cornuta, and water monitors, Varanus salvator, were particularly striking in this regard. Animals in the collection for over 15 years, long in the habit of approaching or ignoring a single keeper in their exhibit for routine maintenance, would flee if 2 people entered. It took but 1-2 incidents for them to learn that 2 people meant trouble – i.e. a veterinary exam, but that 1 person meant no harm. The animals unfailingly retained this knowledge over a period of years, even without reinforcement by new events.


An interesting article on intelligence in monitor lizards is posted at:


  1. avatar

    When I first got my previously owned Blue Iguana hybrid from a pet store in which the employees were constantly removing him from a tiny enclosure to show him to customers and then promptly stuffing him back into that “cell,” he had developed a bit of a dislike for those people. I was warned that he was aggressive and would snap at people if handled. It took me about a week to earn his trust and he turned out to be dog tame. A few months later I took him with me to visit the pet store where I got him, and he was calmly allowing customers and children to approach and pet him. But when one of the employees that he had had the bad experiences with approached me, my iguana nearly lunged from my arms and snapped at him. Clearly he recognized this individual and remembered his bad experiences with the employee.
    Also, on his first vet visit with me he seemed to be a little nervous, as if he had had bad experiences at the vet before. When the vet took out a syringe to show me how to administer the medicine I would be giving him, my iguana suddenly puffed up and tried to bolt off the table. I’m guessing he has had shots before and recognized the syringe and what it meant. Amazing!

    • avatar

      Hello Brianna, Frank Indiviglio here.

      Thanks for your interest in our blog. What a great story – thanks very much for passing it along, and congrats on the fine job you’ve done with the lizard. It shows how much can be accomplished if one goes about it in the right way, and how complex these fellows are. I’ll keep your observations on file and will certainly refer to them often.

      You might enjoy these other Iguana Articles….please check in from time to time and let me know how all is going…

      Good luck, enjoy and please keep me posted.

      Best regards, Frank Indiviglio.

  2. avatar

    Hi Frank,

    How do you think the intelligence of leopard geckos compares to that of anoles? Do you have examples of behavior that justify your opinion?
    Thank you.

    • avatar

      Hi Rudy,

      Sorry for the delay in responding..glitch in the system.

      It is likely that all lizards exhibit learning abilities to some degree (please see articles under “further reading”; Unfortunately, I don’t have any basis to compare the 2 you’ve mentioned, and have not come across any studies on the topic. Best, Frank

  3. avatar

    One friend has a chinese water dragon for some years. When he took her from her previous owner, who fed her only worms, she was eating only mealworms and similar wormlike prey. Gradually she accepted other items, though she hasn’t eaten any vegetable yet. But later on, when she needed to go to the vet and got some heavy examination and injections (I don’t remember the health problem), she became fearful, closed her eyes and played dead. Later, after she passed through this stressful experience, she reverted back to eating worms for a time. When she revisited the vet, she was anxious of the place, and when picked up she would respond as before. For a time later on she trusted only her two main caretakers and not anyone else.
    My crested gecko, of the few times I have given him to others to handle, seemed hesitant to go from my hands to the other’s. He keenly looks at other people going to the room or carrying objects, and I thing he pays more attention when I am carrying something or otherwise change my shape to him. I spot him often watching my rabbit as well. He has learned many other things, for example when I spray the tank he climbs up to the mesh to drink the concentrated water droplets, or knows where the food is placed and waites there soon after waking up. He can recognize insects from afar, and gets ready quickly for his favorites, which are green catterpillars and red runner roaches. He pays attention to the narrow spaces near the hinges created when the door of the terrarium opens, and in the past has tried to squees through that, and nearly got in an accident when I tried to close it. So, I am careful if he goes there, which nearly never does now. He is strange. When I open his door, sometimes wants to get out, but when I take him out, then he wants to jump in. He dislikes being taken outdoors for some sunlight or rain, and when he approaches the specific door turns his head back. But he has learned also bad associations. In his first winter, when I didn’t know much about their natural slowdown, I thought he had constipation and put him in shallow water in the same container I used to feed him insects, which until then he recognized as good and was jumping in it happily. After the experience he was shocked about this box and he would run and jump wildly when placed in, and as time passed, only when I was near. Otherwise in other small containers he was fine. Finally he returned to normal. He has become aggressive or fearful some times for 3-4 days when needed to change place, usually when I traveled. Last summer, I had to remove an unstable plastic plant which I always had to put right again, and the place around his hide lightened and became more exposed. For nearly a month after that, he would wake up with the slightest disturbance, would become very aggressive, and not only nip, but bite, hold and shake like what they do when they fight amongst themselves. After a while he became the same even at night. Gradually he calmed again, and adapted to his much more empty terrarium. Now he has a new plant there.
    My bearded dragon was described to me as friendly towards all from her previous owner, and most probably she is. She is in hibernation now and not interacting with anyone

    • avatar

      Thanks very much for the interesting observations..sounds like you pay a great deal of attention to details that many overlook. Keep it up – we need more of that.

      The type of learning you’re observing is critical to survival in the wild, as you can imagine, but it takes time and effort to notice and understand. We see individual differences and some learning ability in insects and spiders as well. Best regards, rank

  4. avatar

    Yes they have a good capacity to learn. I think people aren’t paying much attention to the details of their behaivior. And if geckos, which aren’t considered the most intelligent reptiles, can learn so many things we can only wonder for the abilities of monitor lizards or crocodiles.
    As the blog needs observations of keepers, I will mention some others of mine.
    My crested gecko, and most probably most others, has a good awareness of his disability when not sticking well, either when before a shed or when it happens that stuck skin from a bad shed interferes with adhesion. Usually before a shed, he becomes more reclusive and tends to climb less, so there is no much problem. But when he is normally active and, by a bad shed, skin remained causing his problems, he knows his problem and doesn’t try to make stunds. The first time having this problem in my care, he fell sometimes from the glass or high from the corners, and from those accidents he became much more cautious. When having that problem he is extremely careful with passing from a gap between two objects, and he avoids jumping most of the time, instead stretching to grasp the neighbouring object. He will only jump for short distances, and only to surface he knows from experience that they are stable, or on the ground. When he regains the ability to jump sometimes in the beginning he might overestimate his abilities and make extremely strong jumps, lose the target and fall.
    I don’t know how good is their depth perception, but everytime he is somewhere unknown and sees the floor a few tens of centimeters below he remains very hesitant of jumping, but when I put my hand down either stationary or moving it and knocking the floor, or a 3d object is down, he can mesure the hight accurately and jump without hesitation. I think that this is the only time I communicated successfully with this species. There were also times, all in the beginning of having the gecko, were he jumped from hights of a meter or more. He didn’t suffer anything, probably because he is arboreal and flexible, he was though shocked and hesitant to move for a short time. Probably these falls are painful. Another time more recently, I was holding him no more than 15 cm from the floor, but he jumped so forcefully that splashed himself on the ground. The shock of the landing made him fearful of jumping for several minutes, where he couldn’t jump even from a 3 cm hight!
    He seems not to have extremely quick reflexes, though I cannot describe them as slow no way. For example, when I described in the previous comment about his aggression, probably caused by fear and stress from the rearrangement of his environment this summer, he would bite me wherever I put my hand in the cage. He would jump right near my hand, and be ready for my misconduct (cleaning, removing eaten food etc), to chase me out of his territory. Other times he struck from a branch, with only the back legs holding him back. But many times, when I managed to pull my hand before he actually bit me, and he had already decided to bite me or was actually in his way, he seemed unable to stop his trajectory and usually hit whatever object was in front of him. He didn’t bite the objects, only he hit them from the momentum he had. But in the hunting of his favorite insects red runners (Shelfordella tartara) or crickets (though rarely I buy them because they are troublesome), he wouldn’t be different from a small hunting mammal, jumping repetedly, turning back quickly, etc. One memorable time, while he was sitting head down on the glass, I through a large red runner in. He moved the head forwards, then immediately jumped on the ground and missed, but immediately he jumped again and caught the insect.
    They show clearly food preferences also for fruits, not only for insects. Mine prefers the very sweet ones, like apricot or peach. Second come fig and banana, and after that any other I have given him. Sometimes it happens that I give him less ripe, so a little more sour fruits, which he doesn’t prefer. I have observed that he will still eat much more the less ripe fruits from his favorite category, like sour peach, rather than other less eaten fruits, like strawberries or apples. Seeds, peal fragments if any and fibers are usually left in the bottom of the bowl, with some being eaten, which pass easily out of the animal because they are too small. In my experience, it seems that they don’t in fact eat rotten fruit, as most caresheets say. When fruit stays for days it becomes brown and gives of an alcohol like odor, perhapse from fermentation. This fruit isn’t touched.
    Another strange experience happened with simulation of a rotting carcass. I have an Orbea variegata succulent, a relative to stapelia which produces carrion smelling flowers too. The first day that the flower opened and I brought the gecko near it, he seemed to smel the air and flick his tongue, showing some interest. I wondered if it is an opportunistic scavenger in the wild, but most probably he stayed because the odor was yet slight, and perhapse he smelled some nectar compounds I couldn’t distinguish, because the other day, when the flower reached its peak, when he smelled it a little only, he turned the head to the side quickly, and started backing off, and this was repeted many times.
    Your observation of reptiles being aroused by novel or wild caught prey is proven in my case as well. Whenever I have given an unknown insect to the gecko, he attacked it quickly, and whenever it was with other familiar insects it was eaten first. I have also observed that such insects, as well as his favorites, are chewed more quickly. But I had a negative experience ones with wild insects. For a time, I was giving my crested gecko flies, the common housefly variety. In August of 2013, the gecko ate a fly normally. But for a minute later he seemed in discomfort, with head tilted up, open mouth and trying to cough. Finally he threw up both the fly and the previous day’s fruit dinner. He didn’t have any lasting problems, as later he consumed 5 mealworms in a row, but that incident made me reconsider flies and other omnivorous wide ranging insects as live food. After a while, when I traveled to a more rural location for vacations with my gecko, I decided that flies there would be more clean and gave him two. I found the one living and the other killed but not eaten after some minutes. I gave another one 15 days later, and again he bit it and left it. He had learnt that this insect isn’t good to eat. But after nearly a year, the past September, I gave him again a fly to see if he remembers it, and he ate it. Probably in the wild they are exposed to the offending insects routinely, so they remember them, but now, where he had months to see a fly, he forgot the negative experience. I don’t know his memory span, but when I had traveled that August for 21 days and returned back, he adapted to his normal enclosure in a day, and the second ate much. From studies I have read turtles can remember at least up to 5 years, so most reptiles might be able of long-term memories.
    But he has still a small brain, and cannot understand some things. He can for example understand that glass is solid – he doesn’t try to pass through it and can distinguish glass from open surface -, but it seems he cannot fully understand that it is a barrier. When he was aggressive for example, he would rutinly watch me intently through the glass and many times he attacked me through it. I then irritated him on purpose, to see if and when he will understand that his actions were futile, and after 5 days the attacks on glass nearly vanished. However, he still attacked superworms from the glass, when I had my hand perpendicular to eat so they could approach the cage, and sometimes I could dupe him by hiding my hand and moving only the end of the finger parallel to the enclosure floor, like an insect. Although that is rare and most of the time he looks the finger and goes away. I don’t know why he tried to eat worms from the glass and not other types of insects. Neither I had success making him eat the mouse pointer as others say about other reptiles. The times he has seen it, he looked it intently, and then started showing signs of fear, turned its head and slowly walked away.
    Geckos are described by scientists as visual hunters with ability to chemically discriminate prey, and that has been proven in my case. In October I purchased for the gecko some superworms, for which I heard both good and bad comments, but I decided to try them. He ate some at first, but then he rejected them, because probably they filled his belly uncomfortably. But even after he stopped eating them, he continued to attack them behind the glass. When though they were presented in front of him and he had the opportunity to smell them, he refused them, either moving away or ignoring them.
    Before nearly two years, in the beginning of having him (he was born July 25, 2011), I had given him two small snailsdifferent days. The one smallest was consumed whole, with only shell fragments left, the other though, a small and thin-shelled yet Helix aspersa, had the top of the shell left. I don’t know how he managed to do that. He isn’t interested in snails generally, so I don’t offer him anymore.
    I think I was helpful.

    • avatar

      Wonderful observations, thank you! I trust, from the detail, that you are keeping notes….we need more folks doing the same. I still refer to my notebooks dating back decades (we all forget details in time, no matter how important, so I write or type everything). Keep up the great work, Frank

  5. avatar

    Yes, I am keeping notes of important events or observations.

About Frank Indiviglio

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Being born with a deep interest in animals might seem unfortunate for a native Bronxite , but my family encouraged my interest and the menagerie that sprung from it. Jobs with pet stores and importers had me caring for a fantastic assortment of reptiles and amphibians. After a detour as a lawyer, I was hired as a Bronx Zoo animal keeper and was soon caring for gharials, goliath frogs, king cobras and everything in-between. Research has taken me in pursuit of anacondas, Orinoco crocodiles and other animals in locales ranging from Venezuela’s llanos to Tortuguero’s beaches. Now, after 20+ years with the Bronx Zoo, I am a consultant for several zoos and museums. I have spent time in Japan, and often exchange ideas with zoologists there. I have written books on salamanders, geckos and other “herps”, discussed reptile-keeping on television and presented papers at conferences. A Master’s Degree in biology has led to teaching opportunities. My work puts me in contact with thousands of hobbyists keeping an array of pets. Without fail, I have learned much from them and hope, dear readers, that you will be generous in sharing your thoughts on this blog and web site. For a complete biography of my experience click here.
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