Monday, May 23, 2011

Hummingbirds in Monte Uyuca

Azure-crowned Hummingbird
After two months of hawk counting on Sandy Hook, NJ, I'm back in Central America, really now my home away from home. I was very happy, obviously, to be reunited with my girlfriend Roselvy, and also to see my good friend Oliver again. They picked me up from the airport in Tegucigalpa Wednesday around noon, and a couple of hours later Roselvy and I were already putting up mist nets in Reserva Biológica Monte Uyuca, not far from Tegucigalpa. This is a biological reserve where we have banded together many times before since Roselvy set up the banding station here in January 2010. Since then, we've carried out monthly banding pulses consisting of 400 net hours each month, most of which I have worked on as a volunteer bird bander.

The station is located in pine-oak forest with a well-developed shrub layer, and is home to many hummingbirds. Five species are found here more or less year-round, although their numbers fluctuate seasonally, in some cases dramatically so.

In May of 2010, we caught more birds (the majority hummingbirds) than in any other month of that year, and we were of curious to see if this surge would repeat itself in 2011. The previous record number of captures during one banding pulse there stood at 202 birds, caught in May 2010.

This May, we caught 217 birds - no fewer than 156 of them hummingbirds!

Besides the expected species, we caught three new hummingbird species for the station!

Many Central American hummingbirds are considered non-migratory, resident species. However, a lot of these resident species opportunistically undertake small-scale movements in search of flowers, which may be locally available at different altitudes during the year. Local altitudinal migration may account for the seasonal patterns we've found for various hummingbirds at Uyuca (Juárez & Komar, 2011).

Azure-crowned Hummingbird

In Uyuca, no species exhibits this seasonal variation more than Azure-crowned Hummingbird. We typically catch a handful of this species throughout the year, but their numbers increase in April and then explode in May. This week, we had 93 captures of this species, with only a few recaptures. We suspect that during the rest of the year, these birds are found a few hundred meters downslope, when the shrubs there are in flower. An afternoon walk in that area, just outside the reserve, seemed to support our conjecture, for we found few hummingbirds and few flowers where both can be very common at other times of the year.

hummingbird's eye view of Palicourea padifolia

Right now, a shrub with yellow flowers (Palicourea padifolia) is blooming abundantly in the area where the net lanes are situated. This plant depends on hummingbirds for its pollination, and provides food for many hummingbirds. It is found in middle-elevation cloud forests from southern Mexico to Panama (Taylor 1989).

Azure-crowned Hummingbird probably breeds in modest numbers right where the banding station is located, but moves into that area - possibly from downslope - in larger numbers a few months after the breeding season. Many adults we caught were either molting or had just finished their prebasic molt. This molt usually takes place after breeding.

White-eared Hummingbird

Another species that shows the same pattern, albeit less pronounced, is White-eared Hummingbird, also a pine-oak specialist. This pulse we caught 37, against only a few during each month the rest of the year.

immature female Green-breasted Mountain-gem

The Green-breasted Mountain-gem shows a different pattern. This species is a common breeder at the bird monitoring station, and we typically catch most of them right after the breeding season, in January and February, when their numbers are augmented with recently fledged individuals. They are present in good numbers most of the year, with a dip in July and August (Juárez & Komar 2011). Possibly this species does something similar to what the Azure-crowned and White-eared Hummingbirds do: it may visit their principal breeding area further downslope in the middle of the rainy season, when flowers in that drier part of the mountain are abundant. Obviously, this is all still speculation at this point, and could be an excellent topic for further study.

The other two species that we catch most banding pulses but do not seem to show any distinct seasonal variation are Magnificent Hummingbird and Green Violetear. While we did catch a violetear, we didn't have the mag this time.

That said, no fewer than three new hummingbird species for the station were found this banding pulse! After more than 6,000 net hours since January 2010, I'd say that is quite remarkable.

adult male Slender Sheartail

One of them was this stunning Slender Sheartail, a species found in southeastern Mexico (Chiapas), Guatemala, El Salvador and Honduras. In Uyuca, we are at the southeastern edge of its range.

adult male Slender Sheartail

Holding this bird in the hand was a first for me.

adult male Blue-tailed Hummingbird

Another was this equally gorgeous Blue-tailed Hummingbird, found in southern Chiapas and in the three countries around the Gulf of Fonseca: eastern El Salvador, southern Honduras and western Nicaragua. This species is usually found at lower elevations, and was certainly a surprise at Monte Uyuca, located between 1600 and 1700 masl.

adult male Blue-tailed Hummingbird

This bird also was in fresh plumage.

Cinnamon Hummingbird

Also more a lowland species - very common even in disturbed habitats like major cities - is Cinnamon Hummingbird. We had never caught this species before in Uyuca, but this pulse caught no fewer than three individuals. The above individual is molting its primaries.

Thanks to José Linares for help with the identification of Palicourea padifolia.

Cited literature:
Juárez, R. & Komar, O. 2011. Monitoreo Permanente de Aves en Reserva Biológica Monte Uyuca, Honduras, durante 2010, primer informe anual. SalvaNATURA, Zamorano, ICF.
Taylor CM. 1989. Revision of Palicourea (Rubiaceae) in Mexico and Central America. Systematic Botanical Monographs 26: 1–102.

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