Sunday, April 12, 2015

The impoverished crown jewels of the desert

You can read all you like about iridescence and refraction in bird feathers (here you are, for a start), but to truly appreciate it, you have to see it. Witness these consecutive photos of a male Anna's hummingbird at a feeder:

Or these, again consecutive, of a male Costa's hummingbird turning its head:

Or, back to Anna's for a moment, forget the now-you-see-it-now-you-don't colour shift. Consider this single picture (all of these, by the way, were taken by Jessica at the Arizona-Sonora Desert Museum) of a male Anna's perched on a branch. I've consulted several popular field guides on my shelf, and there's a consensus verging on unanimity with regard to colour: both Peterson and Sibley describe the male's throat and crown as "red", National Geographic as "deep rose red", and National Audubon, changing the modifier and punctuation slightly, as "dark rose-red". The Smithsonian guide concurs with Peterson and Sibley ("red"), while the National Wildlife Federation goes out on a limb with "stunning strawberry red". I'd have said raspberry rather than strawberry, but okay, we're all agreed on red. Now, Jessa's picture:

I see raspberry, plum, fuschia, orange, olive, bronze, velvet black...all on this one photo of one bird, depending on how the light happens to be hitting each individual feather. Small wonder that hummingbirds made such an impression when they came to the attention of Western science and the general public. British ornithologist John Gould brought his collection of specimens, representing more than three hundred species, to the Crystal Palace in Hyde Park for the Great Exhibition of 1851, though he didn't get to see his first live hummingbird (a rubythroat) until six years later.

As stunning as the Victorians doubtless found Gould's specimens, the birds themselves are even more unbelievable. To reflect upon all that energy—fueling not just the endless dogfighting of these pugnacious birds, the apparent suspension of gravity as they hover before a flower, but also keeping such tiny bodies warm—coming from tiny amounts of nectar sipped from flowers, plus whatever tiny insects they can catch...well, let's just say it tends to give a person a new perspective on sugar water, and I'll be taking a break from Monster and Red Bull, thank you very much, since I have no intention of matching a hummer's activity level anytime soon.

Of course, hummingbirds conserve energy when they can, resting between fights and feeding sessions. They can also go into torpor, slowing down their notoriously fast metabolisms, at night and when food becomes scarce.

Fascinated as I am by predation, I don't think it plays all that major a role in hummingbird ecology.  Hummingbirds are quick, agile, and tiny—a challenge to catch, with a relatively small payoff for the lucky predator who does manage—and the very fact of their bright colouration indicates that finding a mate (or, rather, the mate du jour, since hummers don't form pair bonds) is a higher priority than avoiding the notice of a predator.

Instead, it would seem that that question of energy intake, conservation, and expenditure is the most salient for these little bundles of life. All creatures must balance the books—in fact, by some definitions, that's what life is. In the black = alive; overdrawn = dead. (In this view, ecto- and endothermy—cold- versus warm-bloodedness—represent different economic strategies.) Hummingbirds, though, have to pay more attention to their checkbooks than most. They are the working poor, never far from catastrophe. (And my, how I can relate to that.) As one source puts it, "Hummingbirds are continuously hours away from starving to death and are able to store just enough energy to survive overnight."

So, bearing this life-on-the-ragged-edge-of-disaster in mind, how miraculous is it to have a tiny surplus to pass on?

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