Re: Altitude effects on hummingbird flight?

[evelyn sobielski <koreke77@yahoo.de>]

> ---------------- Good points, although there are a
> lot of willing
> pollinators around here (FL). I like Tyrberg's
> second hypothesis best for
> explaining the lack of re-invasion across the Bering
> Strait. Any hummer
> that happened to cross the Bering Strait in the
> summer
> certainly would be in big trouble if it tried to
> 'home in' on its'
> winter grounds in the Fall. If I had thought of

I'd second that, FWIW.

> that, I never would have raised the issue. Of
> course, that doesn't attempt to explain the initial
> disappearance from Eurasia.

And the sphinx moth argument doesn't fly either.
Except if *they* did evolve in Eurasia too and hummers
became strict flower-feeders in N America only, then
it might. *Where* the specialist lineage evolved is
not known at present; the very basalmost hummers and
modern crown-group forms are all that is known. Hummer
fossil record is good for Caribbean paleobiogeography
and Apodiform radiation, but not much for hummer
evolution itself.

As to disappearance in Eurasia (+ Africa?); and
evolution towards specialization is based on the
bauplan, especially plesiomorphies, you have. Other
lineages stay generalist and fine-tune to the
ecosystem at large, not to a niche. These have a
fairly high chance (if they survive long enough) to
outcompete erstwhile specialists.

Eurotrochilus and relations were semi-hovering small
birds that picked inverts off plants and could feed on
nectar, but they were built in the world of the past.
Such lineages usually survive over evolutionary time
either after mass extinctions (I'm talking Big Seven
here) or as species-poor ones in remote areas.

Regards,

Eike


        
                
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