GWWA in Honduras

The Golden-winged Warbler, according to BirdLife International (the official Red List authority for birds for IUCN), is currently listed as near-threatened. It has "declined rapidly in southern parts of its breeding range in recent years" (BirdLife International 2009).

Local declines of this early successional specialist "correlate with advancing succession and reforestation, and the invasive range expansion of Blue-winged Warbler Vermivora pinus. Other possible causes of population declines are loss of wintering habitat (especially forest edge and open woodland) through agricultural expansion and clearance for plantations, and nest parasitism by Brown-headed Cowbird Molothrus ater." (BirdLife International 2009).

In light of these declines, it is perhaps interesting - though of course largely anecdotal - to note that we saw quite a few Golden-winged Warblers last winter at our Golden-cheeked Warbler field sites. On this blog I even mentioned that in passing here, here and here.

We ended up seeing no fewer than 16 individual Golden-winged Warblers in Honduras last winter. We found the species at every field site we visited. If you've just tuned in, that means five different field sites in pine-oak forest throughout Honduras. At each site, we described at least five different insectivorous mixed species flocks, one per day, and indeed most of our GWWA sightings were of flock members, i.e. birds we found associating with other insectivorous species. The focus of our field work there was the Golden-cheeked Warbler, but we identified and counted all flock members, for a duration of about four hours per flock, over a total of 25 flocks.

At our first field site, in the forests around La Esperanza, we found 3 Golden-winged Warblers. At our next site, Cusuco, we saw 5. In La Botija, our third field site near the Nicaraguan border, we only found one individual. (Most of our locations there were fairly open situations with limited understory.) In La Tigra, not far from the Honduran capital Tegucigalpa, we encountered 4 individuals, while at our last field site, Monte Uyuca, we found 3.

So how does that compare to previous years? After all, this was the fourth year of visiting the same sites using the same protocol.

Well, as some of you will remember, the previous winter I worked not in Honduras but in Chiapas, Mexico. Another team collected the Honduran data. I have the Honduran site reports from that season, and it appears that at least one individual was seen at every site, for a minimum of 5 birds. I'll try to find out if they had more. The year before that, I was part of the Honduran field team and we certainly did not record the species at every site that year. In fact, we only found it in La Tigra (2) and Cusuco (4). The data of the very first year still exist of course but sadly I no longer have them; a computer crash separates me from that year's data. But if memory serves, we only saw 5 or 6 individuals that year.

So that number of 16 for last winter seems pretty good to me.

The majority of those 16 birds were males. In fact, we saw at least 10 males and at least 1 female; 5 birds were not reliably sexed.

With the very strong caveat that this represents only a tiny sample size, it's intriguing to note the skewed sex ratio, isn't it?

My friend - and principal investigator of this Golden-cheeked Warbler study - Oliver Komar coauthored an article describing latitudinal sexual segregation for migratory birds wintering in Mexico (Komar et al. 2005). This tendency of sexual segregation on the wintering grounds is of course well-known in many temperate zone breeders that are short to medium distance migrants. Far less is known about birds wintering in the tropics. Using specimen records from 35 different collections, Oliver and his coauthors found significant latitudinal segregation in nine species, six of them parulid warblers. In all but one case - Indigo Bunting being the exception - males were found to winter further north than females. A popular explanation for the phenomenon is that it allows the territorial sex - males - to return earlier to the breeding grounds, to set up territories.

Golden-winged Warblers winter south of Mexico, and thus were not included in that study. Their winter range is from Guatemala south through Central America to northern South America. Honduras forms part of the northern half of the winter range.

Neither the BNA account, nor the Peterson Warbler Guide, nor the Warblers of the Americas guide mention anything about sexual segregation on the wintering grounds for Golden-winged Warbler. I assume this phenomenon has not yet been studied in this particular species. Our ratio of 10:1 appears suggestive.


Literature cited:
BirdLife International (2009) Species factsheet: Vermivora chrysoptera. Downloaded from http://www.birdlife.org on 11/3/2010
Confer, John L. 1992. Golden-winged Warbler (Vermivora chrysoptera), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/020
Curson, Jon, David Quinn and David Beadle (1994) Warblers of the Americas: An Identification Guide. Houghton Mifflin Company, Boston & New York
Dunn, Jon L. and Kimball Garrett (1997) A field guide to the warblers of North America. Peterson Field Guide Series. Houghton Mifflin Company, Boston & New York
Komar, Oliver, B. J. O'Shea, A. Townsend Peterson and Adolfo G. Navarro-Sigüenza (2005) Evidence of Latitudinal Sexual Segregation among Migratory Birds Wintering in Mexico (Evidencia de la Segregación Latitudinal Sexual en Aves Migratorias durante el Invierno en México). The Auk, Vol. 122, No. 3 (Jul., 2005), pp. 938-94. Stable URL: http://www.jstor.org/stable/4090598

Cusuco

National Park Cusuco was next on our itinerary for this winter's search for Golden-cheeked Warblers in Honduras. We found two goldencheeks there, one of them again an adult male! This brings the adult male : females/immatures ratio up to 6 : 3, a very unusual and intriguing result so far. In this part of the winter range, you'd expect that ratio to be the other way around.

We also continue to see Golden-winged Warblers, more than in previous years. In Cusuco, we saw 4.

But for us, Cusuco this year was marked more than anything else by what we found in the early morning on January 1: someone had broken into the car, and stolen various items, including Kashmir's passport, which he - foolishly, it must be said - had left in his otherwise empty camera bag. (I'm writing this blog entry in the Mexican consulate in San Pedro Sula, where we are waiting for his replacement passport to be processed.)

In Cusuco, we stayed at the eco-hostel in Buenos Aires. I had stayed there before and had fallen in love with the desolate, magnificent view of the valley below. However, the hostel's peripheral location also meant an additional safety risk, and indeed several items we had left out - hand soap, detergent - were stolen. That, and the incessant rain the last four days or so, made our visit a little less pleasant than it could have been. I remember swimming in a mountain stream there and seeing groups of Swallow-tailed and Mississippi Kites overhead, once with a King Vulture mixed in, but that was two years ago, in February. This time, it was often quite cold, misty and rainy, and looking for mixed species flocks was sometimes difficult. Two days were lost because we were unable to find a flock. Our last flock was hard to follow in the pouring rain on a steep slope.

Today in San Pedro Sula we bought a 'new' (used) window for the car, had it installed, and Kashmir made progress with his passport. Hopefully he can pick that up tomorrow and we can continue to our next field site, La Botija near San Marcos de Colón. That's on the other side of the country, so we have a long drive ahead of us, to what I expect will be much nicer weather, and a bit more comfort. In previous years, goldencheeks were not common at this site either, but we'll see.

Ever since day one, we've had minor but continuous car problems. We now have had all four tires fixed. We've had to deal with a broken thermostat, halting circulation of the engine coolant, resulting in an overheated motor on a hilltop somewhere. Still remaining is a right front wheel suspension issue, which appears to be minor. We do need to buy another tool for replacing tires, because the one we had was stolen on New Year's Eve.

Here are some snapshots from Cusuco.

This is a Spotted Woodcreeper, a fairly common species in Cusuco and a regular flock member there.

Yellowish Flycatcher is another common species in Cusuco.

Common Bush Tanagers travel in tight packs and often appear to associate with mixed flocks, although they are also found in single-species flocks. They are somewhat omnivorous and will eat fruit as well as insects.

This immature Broad-winged Hawk was on something it caught on the road, but flushed as we approached. It landed in this oak nearby, possibly waiting for us to leave so it could return to its prey.