RE: Life of Birds (vertical running)

["Tim Williams" <tijawi@hotmail.com>]

Michael de Sosa wrote:

> Because their food sources, nests, water supplies, mates, [etc...etc...]
> were on the ground?
>
> The hypothesis suggests that these tree-runners were ground-based animals
> that ran up into the trees to escape predators, much like some modern 
> ground birds.

Exactly.  Vertical running might be helpful in getting up the tree, but it's 
not necessary to get down.  To reach terra firma again, the predator can 
take a short cut - and this time he (or she) has the help of gravity.

I'd also like to reiterate something Tom Holtz said.  The old "trees down" 
vs "ground up" dichotomy for the origin of avian flight is an historical 
artifact and actually impedes sensible discussion on the topic.  IMHO, this 
aspect of the debate is really about whether flight initially evolved in 
opposition to, or with the assistance of, the force of gravity.

> Eventually some must have spent more and more time up there until
> they became arboreal, but the first ones would have been mainly cursorial
> and would probably go back down once the predator gave up and left.

Or, when these little maniraptoran predators spied a particularly juicy 
morsel themselves on the ground.  Remember, being of a higher elevation also 
lets you keep a better look out for your own favorite prey.  When prey is 
sighted, the little predator could jump down from the tree, and hopefully 
land as close to it as possible.  If not, it could chase it the remaining 
distance over ground.

I'm not putting words in Michael's mouth; this is my own pet theory: Flight 
developing from a method of "sit-and-wait" ambush predation.  So many birds 
do it today - why not their immediate theropod ancestors?

> Or maybe I'm using arboreal the wrong way. I thought arboreal meant you
> spent significant portions of your life in trees, not just a few tense
> minutes every now and then. Am I misinformed? It wouldn't surprise me if I
> just used the wrong word.

As Darren Naish once said, even goats can climb trees.  But nobody would 
call goats arboreal. I don't think Michael de Sosa qualifies as truly 
arboreal, despite his youthful tree-dwelling predilections.  I think to be 
considered arboreal, it has to form an integral part of your behavior.  (I'm 
guessing it didn't Mike - though correct me if I'm wrong  ;-)  )


Tim

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