Friday, September 17, 2010

Green-breasted Mountain-gem

Green-breasted Mountain-gem - Lampornis sybillae adult male

In today's post we're taking a closer look at the Green-breasted Mountain-gem, a hummingbird species that is found in central Honduras (east of the Sula Valley) and northwestern Nicaragua. Closely related to the parapatric Green-throated Mountain-gem, which occurs in Honduras west of the Sula Valley and in northern El Salvador, Guatemala and southeastern Mexico, it is separated from that species by more extensive green mottling on the breast in males, a buffy wash on the throat and more green mottling on the sides of the breast in females, and more contrasting white on the outer tail feathers in both sexes.

Green-breasted Mountain-gem - Lampornis sybillae adult male

Adult male Green-breasted Mountain-gems are stunningly beautiful creatures, whose iridescent throat and breast feathers channel a dull green, or a bright aquamarine or light blue, depending on the angle of the sunlight and the position of the viewer.

Green-breasted Mountain-gem - Lampornis sybillae adult male

Mountain-gems, in the genus Lampornis, are fairly large hummingbirds, one species of which just barely reaches into the United States: the Blue-throated Hummingbird. They are generally associated with highlands, especially cloud forest, and are found throughout Central America. Currently, seven species are recognized, although some work, using mitochondrial and nuclear DNA sequencing, remains to be done on the taxonomy of this genus.

Green-breasted Mountain-gem - Lampornis sybillae young male

Here's a young male, with more or less complete greenish mottling on the throat and breast, like an adult. Both males and females soon after fledging acquire an adult-like plumage, but can still be aged by the presence of buffy edges to the dark green upper head and back feathers, and by the amount of bill striations, or bill corrugations.

Click on this photo for an enlarged view, and you'll notice this bird shows some buffy edges on the head feathers.

Along the side of the bill, little corrugations can be seen that are typical of young hummingbirds. They lose these striations as they get older, and the bill gets harder and smoother. Some adults retain up to 10% of bill striations. The bird in the photo above has a bill striations score of about 60%, and so is very likely a hatch year bird. For some northern species, for example Anna's Hummingbird and Rufous Hummingbird, the timing or rate of this process of bill smoothing is known, and the percentage of bill striations can thus be used to reliably age individuals of those species (see for example Yanega et al. 1997).

In tropical species, however, much remains to be learned about the rate of this process. I'm currently working on a paper about the Green-breasted Mountain-gem's sister species, the aforementioned Green-throated Mountain-gem. In this species, it appears that bill smoothing takes more than one year to complete. Bird banders working in the tropics are thus advised to exercise caution when using rate of bill striations for ageing hummingbirds.

Green-breasted Mountain-gem - Lampornis sybillae adult female

This is an adult female, with a buffy wash on the throat. Females of the more northerly/westerly sister species Green-throated Mountain-gem have white throats, while females of the more southerly/easterly White-throated Mountain-gem have orange throats. Geographically located between these two extremes, the female Green-breasted Mountain-gem appears to be intermediate in that particular aspect also.

Note that this bird has a modest amount (<10%) of bill striations near the base of the bill.

Green-breasted Mountain-gem - Lampornis sybillae adult female

Here an unusually pale-throated female Green-breasted Mountain-gem. A small percentage of females will look like this, approaching Green-throated Mountain-gem in this feature. Note however the green mottling on the sides of the breast and belly; in female Green-throated Mountain-gems, the green mottling generally does not extend beyond the sides of the upper breast.

Note that this bird has no bill striations, but a small abrasion on the distal part of the bill, a mark that's probably the result of some external impact.

Green-breasted Mountain-gem - Lampornis sybillae adult female

And here a top view of the same bird, showing the whitish outer tail feathers, a field mark good for Green-breasted, not Green-throated Mountain-gem. Note that the right outer tail feather is cut. We do this to mark individuals. Special permits are required for hummingbird banding.

All these photos were taken this past week in Reserva Biológica Monte Uyuca, Honduras. I was there to band birds with the banding crew of SalvaNATURA, a conservation NGO for whom I'm currently volunteering. If you want to learn more about the valuable work we do in SalvaNATURA's bird monitoring program, then please visit Maratón de Aves El Salvador / Birdathon 2010 and consider sponsoring the birdathon, which I have the honor of organizing this year. All funds collected in this 8th edition of the birdathon will go toward SalvaNATURA's bird monitoring project. Your contribution will be greatly appreciated.

Cited literature
Yanega, Gregor M., Peter Pyle & Geoffrey R. Geupel 1997. The timing and reliability of bill corrugations for ageing hummingbirds. Western Birds 28: 13-18.

No comments: