A clever foraging tactic in arboreal monitor lizards

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Robert Mendyk
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A clever foraging tactic in arboreal monitor lizards

Post by Robert Mendyk » September 11th, 2011, 6:49 pm

Since some of the participants of this forum aren't members of the SSAR and don't receive Herp. Review, I thought I'd share with you some photos and video which supplement an article of mine co-authored with Hans-Georg Horn appearing in the latest issue.

Basically, we discovered that when presented with an inaccessible prey item hidden inside a narrow tree hole or crevice that's too small for the head to enter, the black tree monitor, Varanus beccarii, will abandon its conventional prey capture technique (the jaws) and switch to an alternative technique that uses a completely different set of motor skills. Some might even call it "mammal- or Aye-aye-like":

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Here are two video clips of the behavior, which better illustrates the whole process:

http://www.youtube.com/watch?v=ilPhdnnS ... e=youtu.be
http://www.youtube.com/watch?v=KlPlYAEXLrw

Although our experiments were captivity based, our findings are relevant to wild monitor lizards since we consider this behavior to be a mutual interaction between insight learning (solving a foraging problem) and instinct (the coordinated forelimb movements). Hopefully someday I will make it out to the Aru Islands to make field observations on the natural history and behavior of this species and possibly observe this behavior in the wild... but for now, laboratory-based observations will have to do.

To tie this discussion of foraging behavior in with field herping, I am curious if anyone here has ever observed fascinating or unusual foraging behaviors in monitor lizards, or any other herp for that matter while out in the field? Have you ever observed a behavior that really impressed you or made you say "Wow" ?

Recently on a herping trip through Thailand, Malaysia and Singapore, I was able to follow around several wild water monitors (V. salvator) as they foraged and weren't bothered at all by my presence. I was impressed by their chemoreceptive abilities and patience while foraging, carefully locating buried prey (beetle larvae, I believe) which was then delicately dug up and consumed.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by mikemike » September 11th, 2011, 7:06 pm

Awesome observations and pics. Thanks for sharing.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by mjd123 » September 11th, 2011, 7:28 pm

Robert,
How long did it take before the lizard used its claw to get the worm? Thats a neat form of behavioral enrichment. Thanks for sharing :thumb:

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Re: A clever foraging tactic in arboreal monitor lizards

Post by monklet » September 11th, 2011, 7:52 pm

Robert, that is off-the-scale bitchen! :shock: WOW! So cool 8-) ... :D :D :D

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Re: A clever foraging tactic in arboreal monitor lizards

Post by Jeremiah_Easter » September 12th, 2011, 6:45 am

Those videos were awesome! I've never seen a lizard use its hands like that, it seemed like I was watching a monkey, not a monitor. Really excellent observations.
Reminds me of other giant lizards...

"That one--when she looks at you, you can see she's thinking--working things out."

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Re: A clever foraging tactic in arboreal monitor lizards

Post by lashinala2 » September 12th, 2011, 6:48 am

Robert, any evidence of 'handedness' in specific animals? I.e. are certain ones left or right handed? Success ratio different for either 'hand'?
I guess the closest I have to a wow is the timber rattler that I keep seeing in a copse of trees in the same area year to year under same weather conditions. She's (horridus) gotta be waiting for something...always the same height (around 6 feet) and always in the same black/honey locusts, and always head up like she's waiting for a bird to land. Herps are pretty ingenious.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by Dan Krull » September 12th, 2011, 6:50 am

I'm reposting these vids using the youtube button above so you don't have to leave FHF to view them. AWESOME STUFF MAN!


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Re: A clever foraging tactic in arboreal monitor lizards

Post by -EJ » September 12th, 2011, 10:04 am

That is super interesting. Does the lizard scrape the food item out or grasp it and pull it out. I know that lizard has the capability to grasp. It does look like a unique instinctive behavior.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by monklet » September 12th, 2011, 12:01 pm

Shared this with a friend who asked a good question...

Was the behavior observed in more that one lizard? If so, were those lizards housed separately? If not, is there any possibility of cultural transmission of an acquired habit?

Thanks,
Brad

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Re: A clever foraging tactic in arboreal monitor lizards

Post by Retes » September 12th, 2011, 12:07 pm

Hi Robert, nice capturing that on vid and stills.

I wonder, how is that different then many many other species of varanids that dig up their prey in all manner of ways.

Varanids and other reptiles do have many many methods of securing prey. Not just what we saddle them with. Varanids being such generalist. That is, are not very prey specific, have all manner of approaches to securing prey.

heck I once saw one of our albig males donk a rat with its tail then go eat it. hahahahahahahahahaha That same male would regularly smack the lite bulbs in his cage. I have to build protection, it was getting expensive.

Anyway, nice going. I got word my green trees are getting close, hahahahahahaha

For Monklet, thats a common behavior amoungst varanids. That is, to smell hidden prey then secure it by digging, pulling etc.

Of interest we have seen and photographed varanids move their eggs by carrying them with their arms. Cheers

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Re: A clever foraging tactic in arboreal monitor lizards

Post by -EJ » September 12th, 2011, 12:36 pm

I don't think it's the same thing. That lizard looks like it is acting with a thoughtful purpose... it tries to reach the food item with it's snout then reaches into a hole with its arm. I think it is amazing.
Retes wrote:Hi Robert, nice capturing that on vid and stills.

I wonder, how is that different then many many other species of varanids that dig up their prey in all manner of ways.

Varanids and other reptiles do have many many methods of securing prey. Not just what we saddle them with. Varanids being such generalist. That is, are not very prey specific, have all manner of approaches to securing prey.

heck I once saw one of our albig males donk a rat with its tail then go eat it. hahahahahahahahahaha That same male would regularly smack the lite bulbs in his cage. I have to build protection, it was getting expensive.

Anyway, nice going. I got word my green trees are getting close, hahahahahahaha

For Monklet, thats a common behavior amoungst varanids. That is, to smell hidden prey then secure it by digging, pulling etc.

Of interest we have seen and photographed varanids move their eggs by carrying them with their arms. Cheers

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Re: A clever foraging tactic in arboreal monitor lizards

Post by Molotov » September 12th, 2011, 2:10 pm

Very nice! I've always thought reptile intelligence was under rated. In some species you can look into there eye's and tell there's something going on.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by -EJ » September 12th, 2011, 2:24 pm

I had an opportunity to see some Komodos and even get a photo with one... the way he looked at me... I declined the opportunity. With monitors... there is something going on inside that 'primitive' head for all of them.
Molotov wrote:Very nice! I've always thought reptile intelligence was under rated. In some species you can look into there eye's and tell there's something going on.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by Retes » September 12th, 2011, 4:45 pm

Hi EJ,

I don't understand, are you saying all the other monitors that dig up or pull out prey are not doing it on purpose. As far as I can tell, they do this very very purposeful.

On only purposeful, but with linerial thinking. For instance, when I kept Odatria, in a huge outdoor cage(ackies, kims, tristis) They were very purposeful in how they hunted certain prey.

For instance ackies are not the fastest monitor around, so they would dig up prey lizards. The fast ones like Whiptails and zebratails, they would first pull of the tail, until it would not break anymore then consume the lizard. But if the prey was not in a burrow, they would poke under one side of the rock and quickly pull their head out and see if the prey ran out the other side. All while undulating their own tail, like a cat. Unfortunately ackies often could not catch running lizards, but the kims could, hahahahahahahahaha the dang lizards did not have a chance.

Another behavior ackies did was, acclimise the prey. That is, not chase the prey until the prey become use to them. Then they would simply walk up and grab the prey and consume it.

Apples to apples, we did throw superworms in that outdoor cage and many would burrow down into the ground. It was common to see odatriads work and dig them up, and even pull them out of branches like the Blacktrees did.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by condyle » September 12th, 2011, 4:55 pm

Another million years and they'll be picking locks!

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Re: A clever foraging tactic in arboreal monitor lizards

Post by -EJ » September 12th, 2011, 5:20 pm

Aren't those monitors?

I'm just saying that particular action seems to have required some complex thought.

It's like the peg boards the shrinks use... you know... squares, triangles... round pegs.



Retes wrote:Hi EJ,

I don't understand, are you saying all the other monitors that dig up or pull out prey are not doing it on purpose. As far as I can tell, they do this very very purposeful.

On only purposeful, but with linerial thinking. For instance, when I kept Odatria, in a huge outdoor cage(ackies, kims, tristis) They were very purposeful in how they hunted certain prey.

For instance ackies are not the fastest monitor around, so they would dig up prey lizards. The fast ones like Whiptails and zebratails, they would first pull of the tail, until it would not break anymore then consume the lizard. But if the prey was not in a burrow, they would poke under one side of the rock and quickly pull their head out and see if the prey ran out the other side. All while undulating their own tail, like a cat. Unfortunately ackies often could not catch running lizards, but the kims could, hahahahahahahahaha the dang lizards did not have a chance.

Another behavior ackies did was, acclimise the prey. That is, not chase the prey until the prey become use to them. Then they would simply walk up and grab the prey and consume it.

Apples to apples, we did throw superworms in that outdoor cage and many would burrow down into the ground. It was common to see odatriads work and dig them up, and even pull them out of branches like the Blacktrees did.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by -EJ » September 12th, 2011, 5:21 pm

Aren't those monitors?

I'm just saying that particular action seems to have required some complex thought.

It's like the peg boards the shrinks use... you know... squares, triangles... round pegs.

I'd still like to know if the lizard grabbed the prey or if it dragged it out?



Retes wrote:Hi EJ,

I don't understand, are you saying all the other monitors that dig up or pull out prey are not doing it on purpose. As far as I can tell, they do this very very purposeful.

On only purposeful, but with linerial thinking. For instance, when I kept Odatria, in a huge outdoor cage(ackies, kims, tristis) They were very purposeful in how they hunted certain prey.

For instance ackies are not the fastest monitor around, so they would dig up prey lizards. The fast ones like Whiptails and zebratails, they would first pull of the tail, until it would not break anymore then consume the lizard. But if the prey was not in a burrow, they would poke under one side of the rock and quickly pull their head out and see if the prey ran out the other side. All while undulating their own tail, like a cat. Unfortunately ackies often could not catch running lizards, but the kims could, hahahahahahahahaha the dang lizards did not have a chance.

Another behavior ackies did was, acclimise the prey. That is, not chase the prey until the prey become use to them. Then they would simply walk up and grab the prey and consume it.

Apples to apples, we did throw superworms in that outdoor cage and many would burrow down into the ground. It was common to see odatriads work and dig them up, and even pull them out of branches like the Blacktrees did.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by Robert Mendyk » September 12th, 2011, 6:15 pm

mjd123 wrote:Robert,
How long did it take before the lizard used its claw to get the worm? Thats a neat form of behavioral enrichment. Thanks for sharing :thumb:
It didn't take long for individuals to successfully retrieve the prey once the conscious decision was made to abandon use of the jaws and switch to the foreclaws. Once the animals realize that their heads are too large for the hole (they seem to quickly learn how to judge this, and the time intervals decrease with experience), they immediately switch to using the forelimbs.

Of course the deeper the hole, the more time, effort and coordination it takes to extract the prey.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by Robert Mendyk » September 12th, 2011, 6:22 pm

lashinala2 wrote:Robert, any evidence of 'handedness' in specific animals? I.e. are certain ones left or right handed? Success ratio different for either 'hand'?
All specimens tested in the study (n=3) successfully used both hands interchangeably depending on their body positioning in relation to the hole, and I did not notice any favoritism that would suggest handeness (although this is not something I specifically looked at quantitatively). For instance, if their body positioning was off centered, and they weren't able to probe the entire depth of a hole with one arm, the animal would switch to the other limb to probe deeper.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by Andy Avram » September 12th, 2011, 6:40 pm

That is a cool video. Makes those reptiles look so mammalian it is almost eerie.

Andy

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Re: A clever foraging tactic in arboreal monitor lizards

Post by -EJ » September 12th, 2011, 6:47 pm

Again... was the prey grasped or dragged out. If it was grasped, which they are more than capable of doing, it would add a whole new element to the action. It is still cool, regardless.
Robert Mendyk wrote:
lashinala2 wrote:Robert, any evidence of 'handedness' in specific animals? I.e. are certain ones left or right handed? Success ratio different for either 'hand'?
All specimens tested in the study (n=3) successfully used both hands interchangeably depending on their body positioning in relation to the hole, and I did not notice any favoritism that would suggest handeness (although this is not something I specifically looked at quantitatively). For instance, if their body positioning was off centered, and they weren't able to probe the entire depth of a hole with one arm, the animal would switch to the other limb to probe deeper.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by Robert Mendyk » September 12th, 2011, 6:53 pm

-EJ wrote:Does the lizard scrape the food item out or grasp it and pull it out. I know that lizard has the capability to grasp. It does look like a unique instinctive behavior...

...I'd still like to know if the lizard grabbed the prey or if it dragged it out?
I'd say it's a combination of the two. From what I've seen in 20+ species of monitors, members of the Varanus prasinus complex (aka "tree monitors") appear to have the greatest degree of dexterity in their foreclaws, and this new behavior certainly supports this general observation. However, as dexterous as they may be, they can't clench a fist and of course lack opposable thumbs; therefore, they're not completely grasping the prey item, but rather curling the digits around the prey to the point where it can be pulled out. What also occurs quite often with both soft and hard-bodied prey, is that the sharp claws impale prey item, where it is then yanked right out of the opening while still attached to the claw, where it is then gently seized with the jaws and swallowed.
-Monklet wrote:Was the behavior observed in more that one lizard? If so, were those lizards housed separately? If not, is there any possibility of cultural transmission of an acquired habit?
This behavior was initially discovered in a male V. beccarii in my private collection. To determine whether this was an just isolated case of insight learning performed by a particularly "gifted" individual or a behavior used across the species, three specimens were tested. The two that were tested from my collection were never fed together and were kept separately except for breeding introductions; therefore, the possibility of learning from one another or some "cultural transmission" as you mention was not possible. The third specimen tested was not even a part of my collection; residing in a collection more than a thousand miles away under conditions that differed from what my captives live in.

One of the things we discuss in our paper is that this behavior seems to be a mutual interaction between insight learning and instinct. Since it was performed by all three specimens and the specific limb movements and body positioning were identical in all three, we contend that all V. beccarii are capable of this behavior, and go even further to suggest that this behavior is probably used by other members of the V. prasinus complex given how similar/near-identical they are in ecology, diet, size and morphology.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by -EJ » September 12th, 2011, 7:03 pm

That is still mind blowing. I do have an idea that they can grasp with those talons which is why I asked.
This was a really entertaining and informative post. Thanks.

You mentioned a paper... has it been published... if so... where?

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Re: A clever foraging tactic in arboreal monitor lizards

Post by Robert Mendyk » September 12th, 2011, 7:10 pm

Oops, my apologies for not posting the reference. It has just been published in the latest issue of Herp Review.


Mendyk, R.W. and H.-G. Horn. 2011. Skilled forelimb movements and extractive foraging in the arboreal monitor lizard Varanus beccarii (Doria 1847). Herpetological Review 42(3): 343-349.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by -EJ » September 12th, 2011, 7:32 pm

No need to... you mentioned it in the opening lines... I missed it.
Robert Mendyk wrote:Oops, my apologies for not posting the reference. It has just been published in the latest issue of Herp Review.


Mendyk, R.W. and H.-G. Horn. 2011. Skilled forelimb movements and extractive foraging in the arboreal monitor lizard Varanus beccarii (Doria 1847). Herpetological Review 42(3): 343-349.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by saratoga » September 13th, 2011, 5:37 pm

Great observations and video.

Are the 3rd and 4th fingers on that monitor longer than normal? Perhaps if they are longer it is specifically for this purpose!

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Re: A clever foraging tactic in arboreal monitor lizards

Post by Sam Bacchini » September 13th, 2011, 6:06 pm

That may be one of the coolest things I've seen in a long time. :thumb:

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Re: A clever foraging tactic in arboreal monitor lizards

Post by vincemartino » September 13th, 2011, 8:20 pm

Monitors are so fascinating with there ability to solve problems. Excellent observation and documentations.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by Cole Grover » September 14th, 2011, 6:17 am

Unreal. Seriously cool observation. The videos make it all the better. I eagerly await my SSAR publications to show up.

-Cole

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Re: A clever foraging tactic in arboreal monitor lizards

Post by TravisK » September 14th, 2011, 8:41 am

Wow, that is incredible! Probably one of the most interesting things I have seen all summer. Those monitors look like mammals when they do that. What a fascinating creature. Thank you for sharing that with all of us.

Regards,

TravisK

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Re: A clever foraging tactic in arboreal monitor lizards

Post by ritt » September 14th, 2011, 9:32 am

Very cool stuff, Bob. Do you know which issue of Herp Review it'll be in? I look forward to reading the report. Have you tried similar experiments with any other members of the prasinus complex, or other species of varanids?

By the way, if you make it to Aru (or anyplace with other species of prasinus complex varanids), good luck trying to do some observations. I've spent spent around three months in a few areas that should have V. prasinus, but have yet to so much as see one (much less try to collect one or make some behavioral / natural history observations on one). Also, in nearly 20 years of working in PNG, and months in the field in a variety of sites, my major professor has only gotten a few prasinus. Perhaps beccarii is more common (Steve Richards might be someone to ask about that, I believe he's been to the Arus), but it seems like unless you get really lucky, observations of even a single individual would be tough at best (not necessarily impossible, but very difficult).

-Eric

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Re: A clever foraging tactic in arboreal monitor lizards

Post by Retes » September 14th, 2011, 11:14 am

I have a japanese friend who has seen thousands of prasinus in nature.

He said, they are very very difficult to see/collect in natural habitat. But very very very common in disturbed habitat. Without going into details, in some areas, they were more then abundant. Cheers

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Re: A clever foraging tactic in arboreal monitor lizards

Post by Robert Mendyk » September 15th, 2011, 7:34 am

saratoga wrote:Great observations and video.

Are the 3rd and 4th fingers on that monitor longer than normal? Perhaps if they are longer it is specifically for this purpose!
While I am not sure if the long and slender limbs and digits evolved in response to this type of foraging (i.e., a potentially unused/open niche), they certainly compliment the behavior well. It could very well be possible that the long limbs and digits evolved with arboreality in the species/complex; however, it should be noted there are many other arboreal species of monitors that have short stumpy legs and digits (i.e., V. gilleni, V. similis, etc.), so long limbs/long digits are not necessarily a requirement for arboreality.

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Re: A clever foraging tactic in arboreal monitor lizards

Post by Robert Mendyk » September 15th, 2011, 7:48 am

ritt wrote:Very cool stuff, Bob. Do you know which issue of Herp Review it'll be in? I look forward to reading the report. Have you tried similar experiments with any other members of the prasinus complex, or other species of varanids?
It appears in Vol. 42 No. 3 which should be arriving in people's mailboxes soon. I have not personally tried this with other members of the complex, but I have with Varanus similis, which does not appear to be capable of performing this behavior- although I will continue to experiment with them. I have asked many keepers- both private hobbyists and zoos to test for this behavior in additional species; I'm curious how extensive it is.
ritt wrote:By the way, if you make it to Aru (or anyplace with other species of prasinus complex varanids), good luck trying to do some observations.
I understand how difficult finding forest monitors in the wild can be, and I wouldn't set high expectations for myself if I were to visit these areas. I recently returned from a seven week long trip traveling through Thailand, Peninsular Malaysia, Sarawak, and Singapore where I did manage to encounter many V. salvator and V. bengalensis out bush, but struck out completely on V. dumerilii and V. rudicollis, even in areas where they were purported to be "very common" by locals. Regarding the prasinus complex, a few colleagues of mine have traveled to Batanta and Waigeo in search of V. macraei and V. boehmei, with limited success. They had far better luck/success when consulting locals to show them where and how they could be located. Locals don't seem to have any problem locating and capturing them, just look at the live reptile trade... I would also imagine it would be easier to spot them in Sago palm and coconut plantations rather than primary forest.

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