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definition of scavenging and definition of fish-eating



S. Friesen wrote:
 
>Well, it is scavenging.  it is also scavenging when they eat something that
died in a flood or of old age, even if they do not have to chase any other
predator away.  (Scavenging is defined as eating something that one was not
involved in killing).
>The problem with saying that any animal that scavenges is a scavenger is
that virtually *all* predators will scavenge if given the opportunity.  (I
have heard it said that some snakes and some mustellids will refuse dead
meat, but I am not sure I believe it).
So, being a large flesh eater, *of* *course* T. rex would scavenge at least
*some* of the time.
>But the usual definition of scavenger is an animal that derives almost all
of its sustenance by scavenging.  This is to make the distinction between
scavenger and carnivore clear an meaningful.
 
 
I would say Friesen's statement is the closest to the true definition.
However, defining scavenging or any other way of getting food is ungrateful task. Most meat-eaters  are opportunistic feeders.  Yet, in the diets of some of the carnivores the meat that came form their own active hunting prevails (like lions), while in the diets of some other meat-eaters like vultures the dead animals prevail. How can one define where is the border among the active hunters and scavengers? 51%?? To me it is almost a philosophical issue. Even among the same species some individuals might hunt 80% and more of its prey, while other members of the same species will scavenge 80% of their meals. Take for instance falcons and hawks. Those inhabited along the highways will live quite prosperously from the road kills and yet, who calls them scavengers. Or take for instance lion herds: in most of them lionesses take care of hunting food, while the old male joins in when the meal is ready - does it make it a scavenger?
The bigger problem is considering the nature of a long gone animal. We even cannot agree which of the living animals are scavenger and which are active hunters.
I came to the similar problem when defining fish-eaters. Baryonyx and Spinosaurus are defined as fish-eating dinosaurs. How can we know? First of all their snouts and teeth are built for catching fish. However, there is no doubt that they caught other animals and scavenged, too. But their primary specialization (anatomy) is what discloses them as piscivorous. The crocodiles and sharks are piscivorous, too, although they also catch and eat other prey. So, I think, when approaching the issue of scavenger or active, one should watch for the primary specialization - the anatomy of the animal: What was it built for? For me, as far as T.rex is concerned, there is no doubt it was specialized for active hunting. T.rex wouldn't refuse dead meat either - the more the better!
 
  
Berislav Krzic
veselinka.stanisavac@siol.net
Beri's Dinosaur World
http://www.geocities.com/CapeCanaveral/Lab/1638/index.html
Dinosaur Books
http://www2.siol.net/ext/zza/index.html