Re: Tail feathers = more pressure on non-avian dinos?

[John Bois <jbois@umd5.umd.edu>]

> From: "James R. Cunningham" <jrccea@bellsouth.net>

> The old style tail would neither help
> nor hinder significantly in this regard. Both tail types can contribute
> to lift at low speed. However, the reduction in stability and consequent
> increase in manuverability due to the new tail might be a big help in
> other ways.  

> At some point the bird of prey will become too large to make
> a vertical launch. Off the top of my head, I'd expect him to wait
> nearby, watching for an opportunity, then launch, gain altitude, swap it
> for airspeed and excess lift, grab the prey, pitch up and swap the
> airspeed back into altitude thus minimising the time near the ground
> (and the adult rhea).  I'm clueless about how they actually do it, never
> having seen these animals.

Here is a piece from Don Bruning describing these hawks and
their modes of attack.  

        "The chicks were in the most danger during the first few days
after hatching.  To survive, they had to keep up with their wandering
father as he frequently covered up to five miles during one day.  Crested
Caracaras (_Polyborus plancus_) posed the biggest threat to young rheas,
being almost always in attendance and waiting for the opportunity to take
one as prey.  The male rhea attacked any caracara that approached too
closely either on the ground or from the air.  In fact, he attacked any
flying object larger than a butterfly--even private airplanes attempting
to land in the vicinity of the chicks.
        Possibly due to the rhea's special alertness toward aerial attack,
caracaras more frequently attempted ground assaults.  They could approach
a group of chicks on the ground more closely than from the air before
being attacked by the male rhea.  A caracara was rather slow and awkward
on a take-off from the ground, while a charging rhea was quite swift.  As
a result, the ground attacks were much more dangerous for the caracara.
The male rhea struck mainly with its bill; but once an object was on the
ground his feet became lethal also..."

You were pretty much on the money--except that they do rely on ground
attack as well.  

One wonders about the size of rhea chicks relative to,
a largish na dino baby?  Certainly the ratio of adult to chick would be
much greater in the non-avian dinosaur.  This would translate into more
opportunities since it would be more difficult for such a big parent to
keep tabs on the tiny hatchlings. I would guess that the mean distance
from parent would therefore be greater in a non-avian dinosaur, and that
this allowed more take-off--or aerial strike time.  But I suppose it could
go the other way.

But the factor that I find most critical would be that a bird of prey does
not need to hover--as in finding small prey--but can camp out on this
horrendously persistent death watch.

If the neornithine tail is not the issue in take-off speed, how
about reduction in mass, i.e., the absence of jaws, etc.

And is it reasonable to hypothesize that neornithines enjoyed improvements
in climb performance and agility as the Cretaceous progressed; that this  
probably meant a reduction in the distance that a bird could position
itself waiting for an opportunity; and that this meant greater
mortality--greater predation pressure on the offspring of non-avian
dinosaurs?



wait for its