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Re: Altitude effects on hummingbird flight?

----- Original Message ----
From: Dann Pigdon <dannj@alphalink.com.au>
To: DML <dinosaur@usc.edu>
Sent: Thursday, December 21, 2006 6:16:03 PM
Subject: Re: Altitude effects on hummingbird flight?

don ohmes writes: 

> Hummingbirds are the largest observed species using hovering, a
> size-constrained locomotion; if some "un-related" group of similar size
> evolved hovering, it seems to me that a high degree of convergence
> would be expected. In either case, I wonder what could have knocked
> them out? Given that hummers occur in Alaska, it astonishes me that
> they never got a foothold in Asia. Anybody know got a clue?

Some (many?) extant hummingbirds seem to be highly specialist feeders, 
sometimes only feeding from a very limited number of flower species. Often 
those flower species themselves mostly get pollinated by hummers alone. If 
one species is reduced in number then the other may follow (if one or the 
other can't adapt to a new food source / pollinator). I can very easily 
envisage a feed-back spiral driving both into extinction in times of 
environmental stress. 

The question really isn't why hummers from other parts of the world may have 
become extinct; perhaps the more interesting question is why such highly 
specialised species have managed to survive (and even thrive) in the 
Americas for so long. Specialists generally don't do so well during 
extinction events. 

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


Dann Pigdon
GIS / Archaeologist         http://www.geocities.com/dannsdinosaurs
Melbourne, Australia        http://heretichides.soffiles.com