Reptile & Amphibian Forums

I have to wonder why varanids have snakelike tongues and related sensory organs(jacobsons organ). Its easy to understand that snakes have this to "see" in the dark, not just at night, but where they spend most of their lives, in holes and such.

I have to wonder if they have these tongues to not just find food, but to aid in keeping track of eachother, it also seems that monitors and snakes(both sexes) both have very developed scent glands.

I imagine, if it was, all about eyesight, then these tongues(organs) would not be needed and they would have short stubby tongues like most other lizards.

So why would monitors have snake tongues? Just something to think about. FR

I was about to reply to SamSweets post below with just such an observation, when I notice this post.

SamSweet wrote that at night monitors are "...just sitting there hoping to not get eaten by something before it gets light. They can't see what's coming after them, and they can't see where to go, which is a bad combination. People who study monitor eyes will tell you that their night vision is just about nonexistent."

Well, I have wondered why they (monitors) have snake-like tongues and apparently poor night vision… and then one night while feeding my Savvy crickets in the dark, it hit me.
I’m nowhere near an expert in this area but Raven was hunting down the crickets with pinpoint accuracy as if she had no problems “seeing” in the dark. I notice that there was a lot more tongue flicking going on than there was in the light. I figure that at night and in low light conditions they compensate for their nonexistent vision by tracking scents.

Come to think of it, how good really, is their vision in light? I think they just “see” movement and shapes anyway, but then again I’ve never studied monitor eyes.

I just assumed that they could “see” in the dark just as good as they could in the light.

Just my .02

Michael

I have said this before, I feel, monitors have really poor eyesight in bright lite. Let me clarify that, at distance, they have incredible vision, but up close, they seem to detect movement well, but simply cannot decern what it is, that is, until they bite it or smell it. Thanks FR

The sense of smell thing wouldn't convince me that they are nocturnal. There are many diurnal snakes that are sight hunters, yet they still have forked tongues and an excellent sense of smell. In fact, there is no shortage of animals out there (whether they be reptiles, mammals or even fish) that have excellent senses of smell and are active by day.

One simple good reason for a monitor needing a good sense of smell is for finding food they cannot see, even by day. Whether it be a small morsel of dead something-or-other lying hidden amongst the visual noise that is leaf litter, or a small animal hiding in a burrow, tree hollow or under a flat piece of bark. They can also track down a mate by the scent left behind, find good basking or roosting spots scent marked by themselves or others, determine whether or not a female is cycling etc etc.

As far as the whole nocturnal/diurnal debate, part of the problem appears to be people wanting absolutes: diurnal animals should never be active by night and nocturnal animals should never be active by day. That's rarely the case with any animal. Monitors are referred to as diurnal simply because for every one sighted at night you'll make 500 daytime sightings. The reason everyone can quote a paper or documentary about night activity is that someone has bothered to write a paper or make a documentary about it because it isn't the norm. You don't see scientific papers with the title of 'Diurnal activity noted in a monitor' because it's commonplace for them to be active by day. I can tell you which of my friends have seen monitors active by night because they've bothered to tell me about it, usually in the form of: "you'll never guess what I saw out on the road last night!" So far, I've yet to hear anyone say "hey, I saw a monitor out yesterday in broad daylight!"

A year or so ago I was out hiking and saw an adult water dragon scoot past in a real hurry. It ran diagonally across my path trying to get away from something else. Not long afterwards, a lace monitor came along following the very same route as the water dragon, moving at a fast walk and tongue-flicking like mad. It was clearly in pursuit, but out of visual range of the dragon and using olfactory (and possibly auditory) cues. It was day time, yet the monitor was using cues other than eyesight to find the dragon. If it could see the dragon it would have been running full tilt after it.

I agree and actually covered most of that. Remember I mentioned It may be easier to help people understand reptiles, by not labelling them, nocturnal or diurnal, but instead, labelling the behaviors they do as such. Because as you mentioned, they DO both.

I also mentioned, calling ones behaviors, predominately nocturnal, etc. Like as you said, monitors are commonly seen in the day.

But you missed a main point I was trying to get across. That is, when inside, are they always sleeping or do they have other behaviors being met. For instance, Lacies commonly inhabit hollor limbs or hollow trees, What else goes on in there besides sleep? Do you think thats where the babies stay until they are large enough to defend themselves? Do you think they feed inside trees? have you ever looked and seen what lives inside these trees? Tell me whats in there? Thanks DK, FR

I believe both terms are purely a label for a behavior not for an animal, "on average their feeding is largely diurnal, but they are known to to forage at night or early morning in the dark". To label any animal that shuts completely down and not responds at all at night to any stimulus until morning light, a diurnal species would be accuate. I wouldnt call a monitor a diurnal animal, Ive seen pics of wild salvators foraging for crocodile eggs, bird eggs, and geckos at night in the dark in India, the pics were taken with a spotlight, there were many adult waters in an area about 100ft square climbing, searching the ground, bushes, holes, eating etc.

"To label any animal that shuts completely down and not responds at all at night to any stimulus until morning light, a diurnal species would be accuate. I wouldnt call a monitor a diurnal animal"

If that were the definition of diurnal, you'd be right.

It isn't.

I think you'd be hard pressed to find a definition of diurnal that insists animals shut completely down all night.

The fact remains, no matter how many documentaries you watch on TV, if you go out into the wild you'll see dozens and dozens of monitors out by day for every one you happen to spot at night, no matter how much road driving you do. Does that odd time you see them out at night mean they are nocturnal? No.

I've seen insectivorous bats flying out just before sunset. That doesn't make insectivorous bats diurnal. Labels such as diurnal and nocturnal are placed to describe the general time of activity, not the exceptions.

In the post I said picture, as in 35mm pictures taken with a spotlight in India.
I aggree its primarily diurnal behavior, but a bad term for an animal. Another generic label.