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Re: Altitude effects on hummingbird flight?

At 07:24 2006-12-21, Guy Leahy wrote: 
The January issue of National Geographic has a
pictorial article on hummingbirds.  On page 126 the
text states regarding one species(the Great
Sapphirewing) that:

"The wings of this high-altitude species are unique
for their iridescent blue feathers and their size:
Thin Andean air requires larger wings and fuller
strokes."

A question... why would this be so?  Does this mean
that above a certain altitude, hummingbird flight
mechanics might not work?  The article does note on
page 123 the largest species of hummingbird is known
to occur at altitudes above 15,700 feet in the Andes,
so it would seem that any altitude constraints on
hummingbird flight mechanics are small.

The article also (on page 122) notes the discovery of
30-million-year old hummingbird-like fossils from
Germany, suggesting that either (a) hummingbirds were
once distributed more widely than the Americas, or (b)
the German fossils represent an extinct group of birds
which evolved convergent flight mechanics to those of
true hummingbirds.

Guy Leahy

Personally I think this is nonsense. The Great Sapphirewing is indeed long-winged and a strikingly fast flier, but while it is montane it is not an extreme high-altitude species, mostly you see it in the upper yungas and at the lower edge of the paramo/puna.
The most extreme high-altitude hummer, the Bearded Helmetcrest which you never see below the paramo and which goes to about 17,000 feet is actually rather short-winged for a hummingbird.
The Giant Hummingbird (the species mentioned in the second paragraph) is long-winged and also goes quite high, but it has a much slower wing-stroke than other, smaller hummingbirds (including the Great Sapphirewing). As a matter of fact it is the only hummer I know where you can actually *see* with the unaided eye how the wing-strokes work in hovering flight and it is quite fascinating to watch. It is also rather unusual for hummingbirds since it frequently glides for short stretches.
Admittedly I haven't watched either the Helmetcrest or the Giant higher than to about 13,000 feet myself, but at that altitude they certainly didn't seem in the least bothered by the thin air.

The question why the Rufous Hummingbird hasn't spread to Asia which was taken up in another message in this thread has probably two answers:

1. It is a forest bird. it is doubtful whether forest has ever extended continuously to both shores of Berings strait at the same time, at least since the Pliocene. If it has happened it would have been during the warmest interglacials (e. g. MIS 11) when the strait would also have been at its widest.

2. It is a tropical migrant. It is apparently quite difficult to shift wintering areas from one continent to another. The species or sibling species which occur both in Eurasia and North America are all residents or short-range migrants. The main exception (the Arctic Warbler which breeds in western Alaska) migrates back to Asia and then south to South-east Asia. Actually the Arctic Warblers here at the extreme west of the range in Scandinavia do the same, they migrate all the way back to East Asia and then south!

Tommy Tyrberg