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Re: T.Rex Feather Skepticism
My apologies for the confusion. I meant whether any ground nesting
passerines show greater terrestrial mobility as neonates or earlier
feather development than purely arboreal passerines, since this would
be a 'precocial-like' trend (though they would still be considered
'altricial'). I cannot think of any either, but (as is probably
apparent) life history characters are not generally my forte, so I
thought I'd ask those with more expertise.
In any case, I never meant to imply a hard and fast rule, only a common
trend. As you point out so well, altricial, ground-nesting passerines
have means other than early-age mobility to reduce predation (namely,
rapid overall growth). This doesn't actually surprise me much for two
reasons: 1) Since passerines are altricial ancestrally, they may be
unlikely to derive precociality (this has already been pointed out on
this thread) and 2) Given how small many terrestrial passerines are,
especially as chicks, rapid growth and the early onset of flight is
probably more 'viable' than being able to run from danger at an early
age (which would, presumably, delay the onset of flight).
Incidentally, in regards to the previous point about deriving
precociality from altricial lineages: I cannot think of any instances
of a truly 'altricial' lineage leading to one labeled as 'precocial'.
However, I can think of one example of increased precociality, that
being megapodes (which appear to have derived superprecocial life
history traits from a typically precocial ancestor, according to most
avian phylogenies that include them).
On Thursday, September 15, 2005, at 10:13 PM, Ronald Orenstein wrote:
At 05:07 PM 9/15/2005, Michael Habib wrote:
Good point; though altriciality is the ancestral condition for
passeriform birds. The more useful question would be whether
passerine birds nesting on the ground tend to become more precocial
than those that nest in trees. There is variation within passeriform
altriciality, after all.
I'm not sure exactly what is meant by this, as I do not know of any
tendency towards precociality in Passeriformes. It is true that some
ground-nesting birds, like larks, develop extremely rapidly and fledge
at an early age - 8 or 9 days in some cases - probably to limit the
risk of predation, but they are still altricial. Also, probably the
longest nestling period of any passerine belongs to the Superb
Lyrebird, a highly terrestrial species that nests on the ground.