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Re: CLIMBING CLAWS



John Bois writes:

>According to David Wescott who works with these birds, they can, in the
>rain forest be amazingly cryptic even away from the nest.  Certainly their
>coloring is quite "loud".  But I'm not sure you can say it does not, in
>the rainforest, add to their behavioral crypticity.  Firstly, bright
>colors are not bright in dull light.  Secondly, (I'm guessing) a greater
>diversity in vegetational colors might give the cassowary a blending
>effect.  Thirdly, since these birds are not particularly dimorphic, it is
>doubtful that it is a sexually selected trait.  Then, what is it for if
>not crypticity.

Bright colours can serve purposes other than sexual display, including
establishing dominance relationships.  According to the Handbook of the
Birds of the World, "It is thought that this array of gaudy colours acts as
a social signal in the dark rain forest; the colours of the bare parts can
change with the bird's mood."

>These are good points.  However, this guild was probably not as competent
>at locating forest nests as guilds which included eutherian predators.
>All known marsupials have a smaller brain/body ratio than placentals
>(except, I think, insectivores).

I don't think anyone accepts that this difference translates into
"competency".  Snakes are remarkably "competent" at raiding bird nests -
look at the effect the Brown Tree Snake has had on Guam, where it has
eliminated almost the entire land avifauna in a few years.

>I argue, as a valid hypothesis, anyway, that the slightly higher diversity
>of large birds on marsupial continents relative to placental continents,
>is due to this relative competency of guilds.

This won't do.  The diversity of flightless ostrich precursors in Asia, for
example, was once pretty high.  Certainly it is true that flightless ground
birds are more common in areas lacking predators, such as islands, but I
cannot believe this applies on continents.  For example, both Australia and
Africa have birds of prey that smash ratite eggs with rocks (the Egyptian
Vulture and Black-breasted Buzzard, respectively).

--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
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