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Re: Island-dwelling dinosaurs (was Re: Gargantuavis neck vertebra)



Mike Keesey <keesey@gmail.com> wrote:

>> Well, they're all not flightless, and at least secretarybirds and seriemas
>> still roost in trees a lot, IIRC even nest there. No time to look up the
>> hornbills.
>
> I meant as the still-flying-but-can-deal-with-other-critters-on-the-ground
> phase.


Yes, that's what I meant too.  If a bird is predominantly terrestrial,
and can deal with terrestrial predators (including protecting its
eggs), then it might actually be advantageous to lose flight.  Flight
is not only energetically expensive, but it also constrains body mass.


Nevertheless, as the Tasmanian nativehen demonstrates, you don't
always need to get big.  For the nativehen, if you're small and intend
to stay on the ground, it helps to be fast.


Brian Lauret <zthemanvirus@hotmail.com> wrote:

>  What we consider to be normal weaknesses and behaviour for flightless bird
>  on islands may not be particularly applicable to flightless birds that evolve
>  on continents, rarer though they may be.


Yes, nicely put.


Large, flightless, continental birds are rare now; but as your post
makes clear, they were all the rage in the Paleogene.  Some, like the
dromornithids and phorusrhacids, survived until quite late in the
Neogene.  Ratites are still with us in Africa (but not Madagascar),
South America and Australasia.


>  Clearly, these are birds that like *Patagopteryx* appear to prove both the
>   'small flightless birds only evolve on islands'-rule and 'continental
>   flightless birds need to be big to survive'-rule wrong. Likewise, tapaculos
>    have also been considered flightless.


Yes, and tapaculos arose in a continental environment.  Nevertheless,
some tapaculo species are critically endangered.  Nevertheless,
tapaculos have fared better than island-dwelling passerines that were
flightless, or nearly so.  One of these, the Stephens Island wren
(_Xenicus lyalli_) of New Zealand, was famously wiped out
single-handedly (or single-pawedly) by the lighthouse-keeper's cat.
However, it appears that more than one introduced cat was behind the
extinction of this songbird.  In any case, the latter evolved in the
absence of terrestrial predators, and so was vulnerable when feral
cats came along.






Cheers

Tim