[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Velociraptor scavenged azhdarchid pterosaur




On Mar 4, 2012, at 12:45 PM, Denver Fowler wrote:
>> Birds of prey will fairly commonly take prey that are subequal in size to 
>> themselves (which would be the case with a 13kg Velociraptor vs a 9kg 
>> pterosaur). Peregrines take a lot of pigeons, hawks take rabbits; 
>> accipitrines take all manner of large birds their own size, or sometimes 
>> slightly larger. Flight has little influence on the hawks and accipitrines 
>> as they take prey on the ground, and other than being typically rather 
>> surprised have plenty of fight left in them. If you take "large" prey 
>> (subequal size to the predator; that cannot be contained within the foot), 
>> the issue is how do you immobilize an animal that might retaliate? 

Mike Habib replied:
>I was expecting that birds of prey would get mention in the discussion.  Yes, 
>birds of prey do take large prey items.  However, I assert that your 
>supposition regarding the unimportance of flight in this regard is mistaken.  
>Most birds of prey do take prey on the ground, but that hardly removes the 
>importance of flight.  The ability to fly removes a huge component of the risk 
>in attacking large prey.  A bird of prey has a very high probability of escape 
>if the initial attack does not subdue the prey item as expected.  The critical 
>detail here is not what happens when the attack is successful, but what 
>happens when it fails.  Most attacks on large prey fail, but those failures 
>likely carry relatively low risk if the predator can fly and the prey item 
>cannot.

Generally speaking, the predator seems more at risk if prey capture is 
successful than if it is not. Most prey do not seem to want to stand and fight, 
preferring to run (or fly) away. If the prey is somehow unable to escape then 
it may fight, and this is when effective immobilisation is crucial. Falcons can 
stun prey somewhat, if they stoop it from the sky. In hawks, flight does not 
afford any real advantage to the immobilisation process, other than the element 
of surprise. Well, other than stability flapping maybe. I don't think the 
predator needs to wo
 own escape rather than standing there looking a bit embarrassed after a failed 
attack.

Relative prey-predator posture is important. It's pretty cool how hawks have 
learned to place a foot on a prey item's head, to stop that method of 
retaliation; usually when dealing with "large" mammals. With large bird prey 
(where pinning by bodyweight is a more 50:50 affair), the predators always seem 
to get into the position where they are standing atop the victim (almost a 
mating position), with the feet placed between the victims wings. this limits 
the ability of the prey to attack, but I think it also minimizes the prey's 
wings from getting in the way  as the predator is positioned between the 
maximum extent of the upstroke (may also explain mantling; see our 2009 paper). 
This position is also the safest place to avoid attacks from the prey's head 
while giving access to the prey's own neck and back. Contrast this with the 
hyper-dangerous strategy of throat attacks by big cats (where the predator is 
very close to being trampled), or potentially
 attacking organs through the belly: this would kill a prey item more quickly 
but subject the predator to the full capability of the forelimbs, hindlimbs, 
and head. Safer instead to bite down through the back, even if it is mostly 
bone.


>In any case, your point is well taken, but the RPR behavior is applicable (as 
>you noted above) to any prey that cannot be easily contained within the foot.  
>So even in a case were the prey was, for example, 20-25% of the mass of the 
>predator it would count as "large", and your model would be potentially 
>applicable.  I am not necessarily arguing that dromaeosaurids did not eat 
>larger prey than average, only that a specimen of a Velociraptor preserved in 
>the midst of having the snot beaten out of it by a Protoceratops that probably 
>greatly outweighed it in life should not be taken to mean that dromaeosaurids 
>routinely attacked prey substantially larger than themselves.  Suggesting that 
>a RPR strategy might have allowed predation on animals 50% of the predator's 
>mass does not stretch incredulity in the same manner as the assertion that 
>mid-sized theropods went around beating down sauropods or that dromaeosaurids 
>went berserker-style after prey 400% of
 their own mass or more.

I agree completely, but it is worth bearing in mind that the "prey riding" 
observed in various hawks is a viable (and real) behaviour by which a 
dromaeosaur could subdue substantially larger prey.

----------------------------------
Denver Fowler
df9465@yahoo.co.uk
http://www.denverfowler.com
-----------------------------------