Thursday, January 13, 2011

The variable song of the White-eared Hummingbird

female White-eared Hummingbird, January 2011, Montecristo, El Salvador
White-eared Hummingbird is one of the most common hummingbirds of Mexican and northern Central American pine-oak forests, a bird highly characteristic of its habitat. Having spent considerable time in that habitat, I thought I knew it quite well.

But it turns out I hardly know it at all.

For example, I thought I knew its vocalizations, both song and call. I've spent the last four winters in Central American pine-oak forests looking for wintering Golden-cheeked Warblers, and saw and heard this hummingbird all the time.

But a couple of days ago, while banding birds at the pine-oak banding station in Montecristo national park, El Salvador, I recorded a hummingbird song that I was not familiar with. I knew the hard, metallic chip that males produce constantly this time of year. But the insect-like chirp that I recorded on Tuesday is very different. Here it is:

Here's another, shorter fragment of the same bird, singing the same song.

And here's a short fragment (of presumably the same bird) with rather typical feeding calls. These I was already familiar with.

Alexander Skutch, in his fascinating book on birds of the region called Trogons, Laughing Falcons, and Other Neotropical Birds, writes about White-eared Hummingbird singing leks he studied in Guatemala. He notes something that was new to me, but immediately 'clicked' when I read it. I'll quote at length:

Perhaps the most typical note of the male White-eared Hummingbird is a low, clear tink tink tink, sounding like the chiming of a small silver bell. This was the note that I first heard and prefer to remember. Some individuals toll their tiny bells very rapidly, others more slowly and deliberately. But as I became familiar with more and more White-ears, scattered over miles of mountainside, I was surprised by the variance of their voices. Many individuals consistently uttered notes so different from the usual clear tinkle that I did not recognize them as belonging to White-ears until I laboriously stalked the birds and watched them calling. These notes were dull and flat, devoid of the clear timbre characteristic of the species, or high and squeaky, or low and melancholy. One White-ear that I often visited repeated rapidly a harsh, metallic click, a buzz almost painful to hear.

Equally unexpected was my discovery that all members of an assembly sang in much the same way but differently from those in other assemblies.  If one bird of a group repeated a silvery tinkle, his neighbors would be found to do the same; if I was attracted to an assembly by chirping notes, this was the prevailing tune.

from Alexander F. Skutch, Trogons, Laughing Falcons, and Other Neotropical Birds, 1999, Texas A&M University Press, College Station, Texas, USA.

The insect-like song that I recorded is not described in Howell's guide to the region, nor in Sibley's or Kaufman's guides to North American birds. In fact, apart from Skutch's perceptive observations quoted above, most bird guides tend to give succinct, seemingly complete descriptions of its vocalizations. To my ears, none of the other White-eared Hummingbird vocalizations represented in xeno-canto at the time of writing sound like my bird. And although only a single bird can be heard in my recordings, I sometimes heard another one there, duetting with a similar song.

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