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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).

Cheers,
--Mike Habib

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.