More often than not, when crocodiles are gutted pebbles/rocks are discovered in their stomachs. Does anyone have any ideas why this is? I'd be interested to hear the opinions of others, and then I will give my own.

Maybe the rocks help mash up things in order to make digestion easier. Or maybe they are just so stupid that they would swallow anything.

Landrum

To get to the other side?

quote:

Originally posted by Landrum:
Maybe the rocks help mash up things in order to make digestion easier. Or maybe they are just so stupid that they would swallow anything.

Landrum

LOL-I would vote the latter!

Aid in digestion/ballast

Crocs don't have any chewing teeth, so like birds they swallow stones to grind up the food in their gizzards.

/

Okay Alf, you seem to know what you are talking about and you seem certain, but here goes anyway. For a long time I pondered this one and came up with the same reasons given in these posts - it was a toss up between ballast and digestion. Eventually, upon speaking with a more knowledgeable man, I discarded the digestion: that guy said that a crocs digestive system is capable of digesting even the hardest bone, so why should it need assistance. made sense, so I went with ballast for a while. One day, I was talking with my father who is a very knowledgeable guy, and the topic came up. well, my dad had the simplest answer and it still makes the most sense to me. Crocs swallow rocks inadvertedly. In rivers and dams where fish are plentiful, they make up the vast majority of a croc's diet. A very common fish found in African rivers and dams is the barbel (catfish), and barbel spend a lot of time feeding deep, on the very riverbed,as does croc. Barbel are favourite prey for crocs. So, croc comes along, gulps down barbel, and a couple of pebbles in the process......
What do you reckon? I am not suggesting this is proven or anything, I just think it's very interesting. Why do crocs need to balance ballast? They are perfectly balanced in the water from the day they are hatched, without any rocks inside them.....
Just a thought, just a thought.

CMcDermott

I don't know what you mean by chewing teeth, but all the crocs I've seen seem to have more than enough munchers!!!
Crocs don't chew as much as one would think: they tear and twist chunks of meat off prey and gulp down fairly sizeable lumps.
Thanks for the input though, and thanks for your kind words re my story. Read the other one 'Witchdoctors, Vadomas and Elephant Bulls', down the page a bit.
I think I must go to bed. I am in a very different time zone to most of you guys and work begins in a few hours! I can't help it, I love this site! I think I am becoming addicted. There is so much interesting conversation going on. Thanks again, to all of you

CMcdermot

Oh, it wasn't you with kind words about the story, sorry. You see how AR has drained me tonight, I am like a zombie! Thanks anyhow

/

Thanks Alf

As I said, I'm sure you do know what you're talking about. As I'm sure all these professors do. But...I've never really been one for science and I'm still running with Dad's theory. Ha ha. Aren't scientists the guys that try to convince us that the world came about because 2 cells fused? But where did those first 2 come from....?

I meant to write 'life on earth came about', not 'the world'. Forgive me

Furthermore....
A croc is not capable of discerning thought. How does it know how many rocks it should swallow to achieve perfect counterbalance? It cannot of course, and that lends huge weight to dad's theory. Instinct? Maybe it instinctively knows it should swallow some rocks, but it is impossible for it to know just how much weight it needs to ingest. Do you reckon it swallows a few, floats around a bit to assess the result and then dives down for more because it doesn't feel quite balanced?

Then why do birds eat pebbles?

What to make flying easier?!!!

Maybe a long pre-historic connection between reptiles and birds as the evolutionists claim.

Personally, I buy the theory that dinosaurs are related to birds. Evidently, some dino's swallowed stones, so say the Paleontologists. Secondly, birds have gizzards. They require grit daily to help the gizzard grind up grain, seeds, insects etc. Maybe Croc's swallow stones for some of the reasons mentioned, and some we'll never know. Until we can ask one of them, we'll have to settle for guessing. Remember when they said T-Rex was a sluggish moving, upright stumble bum? Look at how theories have changed.

Because boulders are too big, and stones aren't filling.

It's the buoyancy factor. I recently read about it. It's definitely not for digestion since crocs don't have a gizzard like chickens do.

/

This is what the pebbles look like ...



We took these from a croc last year.

Johan

that's quite a heap of pebbles. I reckon that croc was seriously unbalanced.

I gotta think it the bouyancy.

JPK

JPK

Do you mean it, or is it humor?

Do those pebbles help the croc float before or after the cup of zebra?

RayRay,

I really mean it, but put it poorly. I meant that the rocks are to make the croc sink!

JPK

quote:

Originally posted by David Hulme:
Johan

that's quite a heap of pebbles. I reckon that croc was seriously unbalanced.

I wonder if they'll find a cache like that in my ex-wife... she's pretty unbalanced.

This site seems to indicate both ballast and "gizzard stone" functions are correct.
http://www.arbec.com.my/crocodilesturtles/estuarine/estuarine.php

Bahati: You save those stones and sell them as coming out of a croc's belly. You could start a small business that way. . .

"QUESTIONS ABOUT STOMACH STONES. I have recently read about 200 articles about crocodilian stomach morphology, and the stomach contents of living and fossil crocodiles, and also about stomach stones in fossil reptiles like plesiosaurs and brontosaurus. I am convinced that the function of the stones in crocodilians is not yet understood, and that there is a real need for more information.

Hugh Cott concluded that stomach stones in East African Nile crocodiles function as ballast. Many subsequent authors have belittled Cott's evidence and gone back to a popular belief that the stones aid digestion in a manner analogous to chickens eating grit to grind food in their crop. The crocodile stomach is described as being muscular, like a bird gizzard.

Perhaps crocodile farmers know the answer? Do they routinely add stones to crocodilians diet, like poultry farmers adding grit to chicken food? If not, it would be an interesting experiment to compare growth and digestion in two groups of captive crocodiles, one given stones and the other scrupulously deprived of stones. Additional comparison of the kinds of stones, size, hardness, sharpness and color might also be instructive. Do the crocodiles choose one kind of stones over another? How do they get rid of excess stones? Do they defecate stones? Crocodile breeders with multiple pens of captives could control these variables and experiment. If you discovered that captive crocodiles grow to marketable size more rapidly on less expensive food if they are offered a certain kind of stones, it would pay for the experiment.

Some wild crocodilians do not have stomach stones, but instead have nuts, hard pieces of wood or hard undigested food items. An additional question concerns Cott's ballast theory. He found that the quantity of stones in Nile crocodiles was always around 1% of body weight. If captives have unlimited access to stones, do they eat a fixed percentage of body weight? or does the percentage vary under different conditions? The effect of ballast is probably more significant for wild crocodiles that may contend with river currents or varying salinity and buoyancy that may have an influence on fitness in a demanding environment.

Field reports on stomach contents should include data on rocks. Rock type, hardness, scratches and wear, and color should be noted. Are the rocks all the same? Are they similar to rocks common in the environment or are they brighter, larger, softer than average? The published data are generally deficient in such details. Typically, anecdotes describe how the biggest crocodile had a really big polished stone in its stomach but the quantity and relationships to other material is not reported.

Additional useful information can be gained from X-rays which clearly show rocks. Comparison of seasonal differences in living crocs would be interesting. I recommend a series of still X-rays of comfortably resting animals rather than attempting video tapes of digestive motions. A fluoroscopic motion picture of a caiman digesting a mouse at Yale University was made around 1968 but the observations were never published, although it is mentioned in the popular paleontological literature. The observations were said to be inconclusive because of the interference with natural digestion by the equipment and procedure.

My reading has created more questions than answers. I suspect that too many different kinds of reptiles are being compared, although comparisons with other rock eating vertebrates would be instructive (for example some fish, seals, sea lions, penguins, mutton birds and some sharks have stomach stones). Any information that readers of the CSG Newsletter can provide to this publication would be appreciated." -- Franklin D. Ross, Boekelstraat 14, 2131 WT Hoofddorp, The Netherlands.

I have to damit that i dont know squat about crocs but from that picture above how could so little amount of stones act like ballast, dont crocs weight many hundreds of pounds if not in the thousand pound range? Just an observation.......

It is definately not accidentally ingested, why do Caprivian (sandy region) also have about 1% bodyweight stones in them? Why can young/ small crocodiles (without stones)not float horizontal in water, but big crocs (with stones), can? I believe the stones helps with this, so I would say the ballast teory is about right.

I asked a croc farmer in Otjiwarango that very question !
He said no, ( and laughed) he does not give his little crocs stones as they dont need them to digest the fish and meat he feeds them, nor do they need ballast in the concrete pens they are in. His breeders, in an outside concrete pool do have and take on stones even though there are no live fish on the bottom to mistakenly scoop up. Looks like ballast wins out.

Gentlemen

Far from being close to back-pedaling in the face of all the 'evidence', I am going to have to leave this question open to debate until conclusive proof (one way or the other) is provided. None of the arguments are actually conclusive.
Karl, I don't know about your young crocs in Namibia, but the young crocs that we farm here can certainly float horizontally. They don't spend a lot of time doing it, but they do it. In any case, floating horizontally would surely be rendered more difficult with stone ingestion, not the other way around, if you get my drift! Forgive my ignorance, but do sandy regions have no pebbles? I don't really go with that one, I'm afraid.
TSJ, your argument is more sound but does not convince me entirely. Crocs could still unknowingly scoop up rocks, even if there are no live fish in the ponds. It would be interesting to take two specimens of the same age - one bred in captivity and one from the wild - and compare the amount (weight) of pebbles, don't you think?
fgulla, I like your theory that a pound or two of pebbles could not possibly affect the balance of such a heavy creature. A Nile crocodile can weigh up to 8oo kgs, what is that in pounds? Would anyone like to hazard a guess as to the weight of that pile of stones in the pic posted by Bahati?
I am not refuting any of what you say gentlemen, because I don't know, but I am now running with Nickudu's above 'curve-ball' post: there is simply not enough evidence either way. I agree that we can probably trash the digestion theory.
The response to this post has been great, thank you very much for making it so interesting. I am going to get in touch with a couple of croc gurus here and see what they have to say. I will let you know what their opinions in due course.

Yours in reptilian mystery

Dave

Karl S

1% of body weight? I don't think so. In a fully mature croc that would be 5/6+ kgs of pebbles. Unlikely, I think. In my experience, big crocs usually have the same amount of rocks in them as those shown in Bahati's picture. Bahati, can you tell us how big that particular croc was? And what would you estimate those pebbles to weigh? I am off to collect and weigh a similar pile right now!

Dave

Dave

1% was taken from a previous quote, and I seem to recall reading that weight somewhere before. You will definately have more time to view young crocs than I do, so I believe you if you say they do float horizontal. Those that I have observed in the wild, have not, beause of lack of ability, or some other unknown reason, I really do not know. I thought that a bigger croc have more body fat, which I recon would "float" more, so it might need something like stones to help with the ballast. Surely an interesting topic, I hope we can find an answer. Looking forward to see what your pile weighs.

Karl

Like I said, I don't refute any of what anyone has said here. I simply don't know the answer, that is why I brought the topic up. I live and work with a bunch of guys who have many lifetimes of bush experience (as I'm sure you also do), and none of them has a watertight answer. I do see small crocs floating horizontally. Not often and I don't think they maintain the pose for long, but they do it. Have no idea about the 1% stat, just ahrd to believe in a big croc, that's all. Needing stones to negate bouyancy created by body fat does make sense.........I just don't know. Ivan Carter, where are you? He would probably know more than most of us and he is a member here. Maybe he'll pick up on this thread. Thanks for your input Karl, it sure is an interesting topic.

Dave

quote:

Originally posted by David Hulme:
Bahati, can you tell us how big that particular croc was?

Dave

I think it measured 12'8" or so. Here the guys are busy skinning and salting the croc. The "normal" stone yield is probably between 4-5 cups - or about 2 heaped handfulls for crocs in the 12-15 foot range.



I'll get the guys to collect some stats this year on the "crocrocks" as we hunt a few every year. You normally only watch from a distance as the stomach is cut open ... as the smell is really f*cking terrible!

David,
I'm not sure how accidental it could be? The crocs are in a concrete pool with some sand in certain spots. The rocks were placed in a pile on a sandy patch. The crocs would spread the pile around looking for the rock they wanted. I dont know, I suppose they could be looking for little lizards and ingest a rock that way, but I would doubt it as they are well fed.

TSJ
Yep, well, obviously not accidental if they're spreading them out and choosing particular rocks! Jeez, makes you wonder eh? What did I write earlier? Crocs are not capable of discerning thought? Your comment kinds of puts that one to rest eh? Having said that, I think I'm going to have to put this one to rest, as I have run out of steam. Don't worry, I'm not surrendering, just consolidating! I have to go back to the drawing board and return with more ammunition! Seems I'm not as smart as I thought, need to do more research. I hope someone is able to dig up some more controversial info soon......

Dave

Bahati

Thanks for the input, those photos are great. There's still much to be laid to rest, I can't go with the pebble/body mass stat of 1%. It would be good if you could do some research this year. I should come across a few croc corpses this year and will also find out what I can. Maybe we can start a croc/rock database, or something.
An aside: There is no animal that I have more repect for than a crocodile.
Another aside: Have you ever taken the heart from a freshly killed croc and put it in a bucket of water? I guess hearts differ, but some hearts have been known to pump water for quite some time after croc has been pronounced dead. Notice for how long they twitch and jerk around at the skinning shed. True dinosaurs, for sure. This thread has inspired me to learn more about these amazing creatures. I could get a very good article from all this.

All very interesting, but I don't think anyone really knows for sure, and one theory is about as good as another. IMO, since a crock lives so long, and habitually catches his prey along shore lines, with sudden launching grabbs, the stone are simply scooped up as he feeds. Since he is a swallower, instead of a chewer, the stones are simply swallowed along with wht ever he catches. Over time the stone collect, and do not digest. I think you will find the type of soil, along the rivers/lake shores where he lives most of his life will show in the type, and amount of stones found in his belly. To me, that makes far more sense, than thinking a croc decides which stones to swallow, but like every opinion, of both readers here, and scientests in the reports, I don't know, but I don't think they do either!

AHHHHhhh the mistories of the wild!