Re: Tyrannosaur hunting strategies (was Re: How Did Hadrosaurs Survive?)

[Brett Booth <brettbooth@worldnet.att.net>]

For some reason this didn't show up until Sunday.



on 11/1/02 9:03 PM, Dann Pigdon at dannj@alphalink.com.au wrote:

> Warning! Warning! My sensors detect rampant speculation ahead!
> 
> Brett Booth wrote:
> 
>> But they appear to have more in common with modern birds and
>> mammals than crocodilians. So they can be compared to those animals, we know
>> of no reptiles that hunt in packs.
> 
> Crocs can hunt in groups, and even specialise their tasks. Smaller ones
> chase mammalian prey into deeper water, while larger individuals wait
> down stream to finish them off. They usually do this when herds of
> herbivores cross rivers during annual migrations. I doubt it is true
> "pack" hunting, but it does the job quite nicely. Even when scavenging,
> they work together and specialise tasks. Large crocs clamp down on the
> carcass, while others twist pieces off. They'll even work together to
> chase lions off a kill. There's not complex communication involved. Just
> a combination of instinct and experience.

I've never heard this, everything I know on crocs says that they are highly
canniblistic and would just as soon eat the young croc as the mammal. I know
they will share a kill like komodo Dragons, but from what i know they don't
hunt coopertively. They hunt and capure an animal and the other crocs in the
area come over and 'help' eat the food.

>> If you are going to postulate that rex
>> was a pack hunter, it pays to look at modern pack hunters, since we are
>> unable to look at extinct ones.
> 
> There are no modern predators that even come close to a Tyrannosaur
> analogue. Thinking modern may not be the way to go, and may simply limit
> our ability to postulate new theories (like this one).

Why not? Just because it was big? It's food was big. I think Lions and
Tigers, who usually hunt similar sized prey, make a great example. At least
you can make some basic scientific claims and don't need to invent a new
hunting technique, never seen before, just for T. rex.

 
>>> Young juveniles (say, a year old) could have concealed themselves and
>>> watched, or been used to scare up prey to determine which ones were
>>> easiest to hunt. Animals that are several years old, but not full
>>> adults, could have guided them, since they probably had several years
>>> experience themselves.
>> 
>> And where do these young juveniles, just a year old, learn which animals
>> will make good prey?
> 
> That's the point. Their hunting skills would be crude, so they'd charge
> about making lots of excited noise. The prey animals recognise them as
> juvenile tyrannosaurs (just as crocs recognise juvie hippos and know
> that adults can't be far away), and start to panic. In the panic it
> becomes clear which animals are fit, fast and smart, and which ones lag
> behind for whatever reason. Then the sub-adults take over, persuing prey
> items accordingly.

And what if the juviniles die? Or it's a new mated pair with NO offspring?

And you just don't run into a heard and scatter them, you have to drive them
to the 'killers.' No animals just scatter the herd, they make their choices
BEFORE they start, then if that ones gets away they regroup and make another
choice. You're making T. rex out to be MUCH more complex than any modern
animal. Now I think T. rex was halfway intelegent, but this goes way beyond
that. You're bassing there entire existance on the young, and that just
doesn't work for me.
 

> Cheetahs learn how to hunt within a couple of years, then go it alone.
> As do leapards. Animals may hunt quite successfully before they reach
> full sexual maturity.
> 

Yes, but they aren't hunting in a pack, that requires different techniques.
It still doesn't explian what happens when the chain of babies is broken.


>> To have the entire pack depend on the young ones for
>> sustenance makes absolutely no sense.
> 
> Not really young animals. Just the "teenagers". And they may not
> have relied on them, just taken full advantage of what abilities
> their group members may have had. If sub-adults were faster
> and had better endurance, then why not utilise the fact? Why do
> anything if you're big enough to force others to do it for you? :)

Your supposing T. rex lived in large packs, any evidence for this? why would
they really need to be that fast? The animals they are hunting aren't
exactly speedsters. But again, if there are no young, how do the big ones
eat? 
 
> Besides, alpha lion males, and elderly lionesses, hunt less often
> in a pride. The large size and impressive mane of the male is
> great for defence or intimidation, but they slow them down a
> bit as predators. That doesn't mean that adult male lions can't
> hunt at all. They can survive by themselves if need be. However,
> when in a pride, it is the younger and smaller females that do
> most of the active hunting stuff, since they're better at it.
> The larger male concentrates on defensive behaviour - whether
> it be a carcass, territory, or others in his pride. Any social
> animals will take full advantage of the best attributes of
> their members. Those that hunt best, hunt. Those that have
> better defensive capabilities defend. Of course the defenders
> can hunt when they have to, and the hunters defend, but if
> there's someone else about who is better at a certain task,
> then it makes sense to let them do it.

Yes, but why risk loosing a kill due to adolesant stupidity? You never see
young Lions, wolves ect. hunting with the adults. Why? Becasue they screw it
up, you don't eat and you die. The sub adults might be allowed to watch, but
not participate until they were were versed in the technique. And why would
you have the inexperianced sub-adults teach something that the adult were
much better at?



>> Pack hunters also do not just 'scare
>> up' prey to determine which ones could be readily killed; by the time they
>> make a run at a herd, they have already picked out an animal and are testing
>> their assumption. If their assumption is wrong, they fall back and regroup
>> to try again.
> 
> That's one theory. Based on some modern animals. Besides, I've seen
> dingos hurl themselves into a flock of magpie geese. The fit animals
> react quickly and fly off. Sick or injured animals become apparent
> immediately. I expect that arctic foxes do something similar, since the
> geese can generally see them coming with not much cover about.

 But that's not really hunting in a pack is it? They aren't collectively
bringing down the birds, they're just running in to see if they can grab a
few. You don't need a pack for that, any house cat can do this.

>> A male (or female) grows to adulthood and leaves it's pack
>> to start it's own family. It meets up with a mate and they produce young.
> 
> Outside of an established group, sub-adults may be able to breed. A one
> year old wolf can breed, but doesn't get the chance if the alpha pair
> are around. Send it out by itself and it gets the chance.
> 

Not really, MALE wolves might breed at that age, but females take 2 years
before they have their first heat. But since they are able to breed wouldn't
that make them adults? Animals generally don't work like humans in this
aspect. 


>> If
>> the adults are incapable of the 'flushing the prey' behavior, who teaches
>> the babies? And how do the adults eat until the babies are old enough to
>> participate in hunting? How do the adults even feed their babies in this
>> case?
> 
> They pick off smaller prey, until their offspring are old enough to join
> them. The complex pack-hunting of really large prey is worked up to
> gradually. Arctic wolves raise young in pairs, hunting mostly rabbits.
> Other wolves hunt in packs, and can bring down items larger than
> themselves. Even lone wolves manage to survive. Being a predator means
> being flexible.

If they can pick off smaller prey, which is most likey faster and quicker,
why not just hunt the Big stuff? Plus you can't feed the chicks with just
small stuff, not at that size. They need a big kill to feed everybody.
Arctic wolves will hunt larger prey like moose, it depends on what's in
their area, I've seen them do it (in fact the male was 14 years old!)

>Being a predator means
> being flexible.

Yes, so why would they be so INFLEXABLE as to only hunting the big food
items with the young?If they're so adept at hunting fast small animal and
they have the ability to bring down large prey, why not just hunt the big
stuff?
 
> Besides, in social animals (and we're assuming the tyrannosaurs were
> social - a BIG assumption), it's not just the adults that help feed
> young. Offspring from previous years also help out. Year-old wolves
> will regurgitate for the pups.

It's not a big assumption, they have several T. rex sites with multiple
animals, they have a site with 12 Albertosaurs, seems like pretty good basic
evidance to me. So why wouldn't the sub adults stay home and guard the
juviniles, like modern animals do.

> Magpie geese actually nest in threes -
> the breeding pair, and one of their offspring from the previous
> year. They all help in raising that years offspring.
>

So do coyotes, but geese don't hunt in packs. The yearling coyotes stay with
the new young while the adults go hunting.


>> T.rex was as big as most of the food items it hunted.
> 
> Most? How do we know what tyrannosaurs habitually hunted?
> There is no rule that says a large predator needs to always hunt
> large prey (wolves mostly eat things like mice).

That is a myth, wolves eat whatever food is in the area and what season it
is. If there are large animals in the area wolves will prefer to hunt them.

So what you're saying is that to hunt a large animal T. rex had to have
juviniles? I'm not bying that, if they only ate small animals what would the
be, Gallimimus? If they're doing so well on these small food items why
switch to the larger ones?
 
>> What would the advantage be in having such an extended
>> family together?
> 
> Complex pack-hunting of really large prey. Share the risk about.

Why risk the inexperiance young if hunting is so risky? Not very good
parenting is it?


>> Why would you need anything more than a small family pack?
> 
> You wouldn't, necessaarily. A large group can do things that a smaller
> group might not be able to, but the smaller group can still get by using
> other hunting strategies. I'm not suggesting that tyrannosaurs had just
> one strategy. A successful predator needs to be flexible.

But you need to look at the food items, would they support large packs?
Maybe, maybe not. Butwhat evidance we have is more for small family groups.
One or two T. rexex is plent big enough to kill anything in it's echo
system, why would you need a large pack?

>> You're also assuming that they would produce young every year, so there
>> would be an endless supply of juveniles to scatter prey animals. What
>> happens if there's a bad year and the babies die?
> 
> They don't have to breed every year. I'm guessing a tyrannosaur took
> several years to grow into a 12m monster. In fact, young juveniles may
> have learned more from their siblings that are two or three years older
> than themselves than they would from last year's hatchlings.

Well, since we have no idea how long they took to gro up, I'm not going to
speculate on this one;)


>> Who feeds the adults then,
> 
> Adults simply employ other hunting strategies, if required. Why not
> scavenge for a while?

So while waiting for the babies to grow up, say a year and a half, the
adults scavenged? Not very likely. They'd have to sit around waiting for
food to die, plus feed the chicks, scavenging alone just can't support large
animals.


>> .. and who would the babies learn from if there were no sub-adults around?
> 
> If tyrannosaurs had an alpha pair, and they took many years to reach a
> size capable of challenging them for breeding rights, then they may have
> remained sub-adults for several years. Amongst mandrils, males only
> reach sexual maturity if there is no dominant male around. When the
> alpha male dies, one of the younger males suddenly has a growth spurt,
> becoming larger and developing his "war paint". It actually happens
> quite rapidly. 

Yes, but wouldn't the big female rex be his mother? You still didn't answer
the queston, who teaches the babies how to hunt if their are no sub adults
to teach them? 


>> What
>> if there's a small litter or clutch or whatever you want to call it and the
>> single surviving juvenile is killed or injured during hunting? Hunting is
>> dangerous. What about disease? Young animals tend to be more vulnerable to
>> disease than adults, what happens when disease sweeps through the pack and
>> kills the young ones? Do the adults just roll over and die of starvation?
> 
> No, because... yep, you guessed it - they can employ other food
> procuring strategies. Ambush animals along a game trail. Steal from
> other carnivores. Turn on each other, if need be. There's more than one
> way to feed a tyrannosaur.

Why are you so adverse to them hunting down a hadrosaur if they needed too?
I'm sure they scavanged and I'm sure they ambushed, but even an ambusher
needs to be able to run if the food isn't comming right at them.

>> It's a huge risk and makes the forming of new packs or
>> family groups totally unlikely, for the adults to depend so heavily on the
>> juveniles for hunting success.
> 
> They wouldn't depend on them. Just utilise their greater speed and
> agility. If it's not there to be utilised, then do something else. But
> if they do happen to have a bunch of spritely sub-adults, why not
> maximise their hunting strategy by assigning specialised tasks
> (flushers, chasers, killers, defenders of the carcass).
> 

 Why risk the young like that, taking say a 20 foot juvinile and placing it
into a herd of 40 ft hadrosaurs is very dangerous. The juviniles would
easily get trampled if not VERY careful. Again why risk the young like this?


>> In that scenario 'd have to assume that rex
>> was mainly a scavenger (which I totally disagree with,)
> 
> Most modern carnivores ARE mostly scavengers. Why turn down a free meal
> if you can get it?
> 

No, they are oppertunists, and they only scavenge when they find an easy
meal or can't kill it for themselves.


>> and the juveniles
>> were used for hunting only when the adults were unable to find a carcass or
>> steal one from another predator.
> 
> Or the other way around. They scavenged, or resorted to other food
> procuring strategies, if they didn't have a group structure that allowed
> for more complex hunting strategies.

You can't have the largest predator in an echo system scavange for a living,
the land would be over run with herbivors. It just doesn't happen,
Scavengers are usually small so they can survive off the meager food they
get.


>> No, that's called special rules for T. rex, who was evidently so intelligent
>> and such a good hunter that it was successful despite the welfare of the
>> entire group being placed on the shoulders of the young'uns.
> 
> Adult male lions do less hunting than their offspring. Besides, maybe
> that was why they layed lots of little eggs. Any given ecosystem can
> only support a given number of carnivores, even fewer if they happen to
> be large animals. If only a couple of animals survived from each clutch,
> in a few years you'd have a sizable group. So what it a few get killed?
> That's the life of a carnviore, and since they probably layed lots of
> eggs at any given time, there would have been plenty of young'uns to
> spare - probably too many, actually.

But what if a desease runs through? All the babies would be very vunerable
and most would die, then the adults can't eat. Or another animal raids the
nest and eats all the eggs?

> Of course what you have to keep in mind is that is is merely a theory.
> I'm not suggesting that this is definitely what tyrannosaurs did, or
> that they only used this strategy. They may not even have hunted in
> "packs" at all. Hell - they may not even have hunted, period!

It's a theroy that, to me doesn't hold up in a real echo system. The
scavenging thing is a differnt argument all together (hyenas are not
scavengers anymore than wolves are!)


> In fact, here's another theory: sub-adults chased prey into one of
> several waiting adults (which are scattered about in strategic places).
> The adult grabs the prey (in this case an Edmontosaurus) by the tail,
> and uses its bulk to hold it steady (or as steady as a terrified
> hadrosaur can be). The sub-adults arrive. They would have been too small
> to subdue the prey themselves, but with it held securely by the tail by
> a heavier adult, the more agile sub-adults can nip in and deliver quick
> well-aimed bites to kill the animal. The larger adult is able to hold
> the prey, but may have lacked sufficient manoeuverability to dispatch it
> safely without being injured (and a badly injured tyrannosaur is in
> serious trouble). By working together, and utilising the various skills
> of different tyrannosaur size classes, the predators make a successful
> kill. 

They'd need arms for that. It's WAY too risky. Why risk a kick from a
edmontosaur, why not just have the adults bite the head off. Much less
risky.
 
> Of course, if the adult was unable to hold the prey long enough for the
> sub-adults to arrive, then it may have escaped, bearing the scars of its
> close call. Now if only we could find an Edmontosaur skeleton with a
> healed bite mark on its tail... :)

I think that bite mark would be the mark from hell.

Best,

Brett
www.demonpuppy.com