RE: "PACK-HUNTING" THEROPODS

[Nathan Myhrvold <nathanm@MICROSOFT.com>]

Coordinated group foraging behavior does NOT require a lot of intellegence.
If you doubt this, watch film of army ants bringing down prey MUCH larger
than themselves, in what seems to be a coordinated fashion.   Theropods
certainly had the potential to be as smart or smarter than ants!

Many of the highly intellegent "pack hunting" mammilian carnivores (wolves,
lions etc.) actually do far less actual coordination and planning than once
thought.   The old story, especially as rendered in nature films on
Discovery channel and the like is that lions or wolves carefully planned
hunts, with some group members positioning themselves to cut off prey while
other group members flush them toward the waiting ambush.   It is so cute
and so compelling when you see the nature film that it is hard to resist.
Most people - even biologists - accept it as the gospel truth.

It turns out that detailed observations cast some doubt on this. I can give
references on request, I am traveling at the moment and don't have them with
me - mainly field work by Kruuk, Caro, Packer and many others.  

For one thing, there are many bungled hunts where the group members flush
prey the wrong way, or otherwise work to cross purposes.  Part of the neat
story of cooperation is ex post facto selection by humans that want to see
tightly coordinated behavior.  

Much of the so called cooperative hunting behavior is consistent with the
individuals pursuing individual foraging strategies.   They happen to do
this while tolerating the presence of others.  This looks to a human like
cooperation, but it really very shallow cooperation.  This is also how the
army ants work.  There is no master plan - each ant piles on and tries to
grab a piece.  The collective action of many independent agents can appear
highly coordinated - bird flocking and fish schooling are other examples of
this.

Kill ratios bear this out.   Field biologists have carefully tracked hunting
success.   As one example, a solitary lion has a kill rate of typically
about 15% against most prey (i.e. when they start to hunt or stalk a prey
animal 15% of the time they acutally catch it).  Two lions hunting together
have a 30% rate, which is no more than you would expect if they hunted
totally independently.   They just happen to do it together, without
fighting with each other.   It is hard to call this "cooperation".

The thing that they do cooperate at is in eating together, and in defending
the carcass against other scavengers.

Even more interesting is that three lions have a rate of 30%, and so on with
larger numbers of lions.  There is NO benefit in additional lions past 2.
There are two explanations of this.  One theory is that two lions hunt as if
they each were hunting independently, but beyond that they get in each
others way enough that they individually are LESS successful than they would
be hunting alone.   So much for cooperation. Another theory is that when
more than two lions go hunting, a bunch of them are slackers, who basically
want to pretend to hunt alongside, but will hang back from the actual kill
(which is energetically expensive and dangerous).   Again, so much for
cooperation - the additional "cooperators" are really freeloaders.  There is
observational evidence that supports both views, so the situation is
probably a mix of the two.

Similar statistics hold for other measures of hunting success - kg of meat
consumed per day, distribution of kills per time and other measures. 

Another way to put this is that even if they DO have some deep degree of
planning and cooperation, the statistics say that they get neglidgible
benefit from it in terms of impact on their hunting success.   

These figures are against zebra or wildebeest.  Against very large prey
(cape buffalo), lions typically do not attempt to hunt them alone, but again
the same principles hold - and past a point incremental additions to group
size give no kill rate improvement. Wolves, hyenas and other group
carnivores have roughly similiar stories.

Anecdotal stories do exist of how very clever various mammilian group
hunting predators are.  It is very tempting to see deep planning and
intellegence in their actions - just as we can see in ants.  As a result, it
is tough to say scientifically whether these observations are valid, or not.

Perhaps lions and wolves and others do have some degree of true cooperation.
If they do, they have hidden it very well from field biologists.  At this 

However the point for revelance to dinosaurs is that MUCH of the behavior of
so called "pack hunting" animals could be had without much intellegence at
all.   Instead of requiring great smarts, the miracle of pack hunting is
simply that multiple conspecifics tolerate each other in the same area.
Once you get tolerance for a group, having each group member pursue an
individual foraging strategy can simulate a great deal (and perhaps all) of
the "cooperative" pack hunting.

Theropods could have been group living and group hunting without true
cooperation.    All they would need is social tolerance, and the ability to
pursue individual forging strategies - like ants do. Arguments about their
intellegence as a reason to doubt theropod pack hunting are thus rather
suspect.

Nathan