Another big flock

We took the day off on New Year’s Day, but today it was back to the harsh reality of looking for birds in the mountains of Chiapas, Mexico. Day two at the Laguna del Cochi site.

Today’s flock was almost a repeat performance of the previous one, with many of the same species. Including another Golden-cheeked Warbler! I have a photo with pine needle clusters in focus, and a blurry blob underneath that is the bird. So it goes.

The bird pictured above is either an adult female or first winter male Townsend’s Warbler. Like many Dendroica warblers – and indeed our study bird, the Golden-cheeked Warbler – young males resemble adult females in plumage.

Today’s Golden-cheeked Warbler was a female – or, I should say, a female-type. Adult males are distinctive, with all-black throats and heavy black breast streaking, blackish also on the upperparts. Today’s bird had whitish fringes on the black throat, especially evident in the center of the throat, and dark olive upperparts. It may have been a first winter male, or an adult female – those plumages are practically indistinguishable in the field. It wasn’t an adult male, like all three previous birds we've seen here.

To get a sense of just how difficult it is to separate males from females, take a look at these museum specimens, from the collection in the American Museum of Natural History in New York City. Left row females, right row males, both arranged from darkest to lightest marked birds. This photo illustrates very well the overlap found between heavily marked females and lightly marked males. Quite likely, the higher birds in both rows are adults and the lower birds immatures.

Again Hermit Warblers in this flock, though not as many as in the previous flock. I got to five today. This bird is also either an adult female or a first winter male. The bib is more pronounced in adult males and practically absent in first winter females.

The entire flock was 60 birds strong. Species with more than one individual in this flock were Blue-headed Vireo, Townsend’s Warbler, Olive Warbler, Brown Creeper, Red-faced Warbler, Crescent-chested Warbler, Wilson’s Warbler, MacGillivray’s Warbler, Bushtit, and Ruby-crowned Kinglet.

Dunn & Garrett (1997) note that Red-faced Warblers join mixed-species flocks in winter, “often with only one Red-faced per flock”. (1) Today’s flock had two, which we were able to separate by the color of the red in the face. The first bird we saw had a relatively dullish red color in the face, while the red on the second bird was much more intense. We saw both birds every now and again during the four hours of flock observation, though never together.

The Birds of North America again has intriguing information regarding this color difference:

Although current field guides suggest that this species is monomorphic, it is dimorphic in face and upper-breast color (TEM, PMB): scarlet (color names from Smithe 1975) in male and flame scarlet to chrome orange in female (TEM, PMB). Colors vary among individuals and may reflect age effects. Juveniles are duller than adults, with head and upperparts sooty brown and nuchal collar and underparts tinged with buff (Curson et al. 1994). Further study of color variation with respect to age or other causes is needed. (2)

Based on this, I’m inclined to think we saw an adult and an immature bird. The BNA account calls this species one of the least studied North American warblers, and it seems even something as basic as plumage hasn’t been described in great detail.

We encounter this species practically every day. I’m going to pay more attention to plumage details from now on.

Finally, here in Chiapas, spring is around the corner: today we saw a female Red Crossbill with nesting material (a small twig), while nearby a male was singing his little heart out. Both in the Old and New World, crossbills are known as early breeders. And since a few days, I hear a Whip-poor-will calling around the house every morning at 5:30 AM, when yours truly is enjoying his breakfast. I'm assuming that bird is also setting up shop.


(1) Dunn & Garrett (1997) A field guide to the warblers of North America; Peterson Field Guide Series.

(2) Martin, Thomas E. and Patricia M. Barber. 1995. Red-faced Warbler (Cardellina rubrifrons), 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/152doi:10.2173/bna.152

Cold!

Several days later at the Moxviquil site, and I’ve only caught a glimpse of a Golden-cheeked Warbler one afternoon. When we revisited that site the next morning, we found Townsend’s Warblers, Wilson’s Warblers, an Oliver Warbler, an Audubon’s Warbler, and a Tennessee Warbler, but no Golden-cheeked Warbler. These birds, together with a couple of Steller’s Jays, a Hairy Woodpecker, an Eastern Wood-Pewee, a Greater Pewee, a Blue-headed Vireo, a Warbling Vireo, a Bell’s Vireo, a Yellowish Flycatcher, a Hammond’s Flycatcher, and a Ruby-crowned Kinglet, were seen foraging around the field pictured above. And yes, that white stuff on the field is frost! I never imagined I would be freezing cold while looking at warblers. But here in Chiapas, at more than 2,000 m elevation, some clear nights are very cold.

Once the sun is out, the frost on the field melts and vaporizes.

In the afternoon, we went into town and I got myself a Mayan hand-knitted woolly hat and matching scarf, which this morning proved very effective.

Here are some mug shots of three of the four members of the so-called virens super-species. They are closely related to the Golden-cheeked Warbler.

Townsend’s Warblers are here in pretty good numbers.

Hermit Warblers are found in pines, which are scarce at the Moxviquil site. Moxviquil is practically all oak woodlands, with some pines here and there. Rare clusters of three or more pines invariably have one or more Hermit Warblers in them.

Black-throated Green Warblers are not common here, although we’ve seen several individuals now.

But still no Golden-cheeked Warblers in our flocks! A Black-throated Blue Warbler, yes - a bird that I'm assuming is much rarer here than goldencheek - but where are the goldencheeks?

A Black-throated Blue Warbler

Our GCWA field season in Chiapas officially kicked off today with the first flock of the season, here in the Moxviquil (“mosh-veekeel”) reserve in the hills surrounding San Cristóbal de las Casas. After having seen exactly zero goldencheeks in Costa Rica, I was eager to see one today.

When we left the field station at daybreak, we heard Wilson’s Warblers chipping left and right, and a little further away several Brown-backed Solitaires were singing their wistful dawn song. Other birds we encountered included a Yellow-faced Grassquit, a Yellow-bellied Sapsucker and some Rufous-collared Thrushes. And more Wilson’s Warblers: that bird is found here clearly in high densities.

However, a real warbler flock was somehow hard to find this morning. When we finally encountered one, it seemed more a loose association of insectivorous birds than a real flock to me. It had a Greater Pewee in it, a bird that calls frequently and is sometimes considered a ‘leader’ of such insectivorous flocks. The other birds were remarkably quiet for most of the time, and only the two Townsend’s Warblers and the two Hutton’s Vireos (and of course the six Wilson’s Warblers) called every now and then. Calling softly was a male Black-throated Blue Warbler, a bird whose main wintering area is in the West Indies and northern South America. I had certainly never seen one as a member of a warbler flock in the mesoamerican pine-oak forest, although I remember seeing one fly over the Cardel, Veracruz hawk watch site last September. That bird was headed this way.

We had lunch (antojitos) in the market hall in downtown San Cristóbal, and then we took a colectivo bus back to the field station. These colectivos are really revamped mini-vans that were originally designed to hold maybe eight people, but now fit 20 Mayans and a tall Dutch guy. Just barely, though.

Late afternoon, when the sun was out and the wind had died down a little, the birding was excellent right outside the field station. The courtyard that yesterday had White-eared Hummingbird now also had Green Violet-ear (another hummer) and Cinnamon-bellied Flowerpiercer.

In trees and shrubs surrounding the field station we found several Townsend’s Warblers, a troupe of Bushtits, a Brown-backed Solitaire, a Gray Catbird, a couple of Rose-breasted Grosbeaks, a Rufous-collared Sparrow, and a Rufous-collared Thrush. On one of the trails we saw a beautiful Red-faced Warbler (an oak specialist) and what appeared to be another warbler flock. We decided to revisit that location tomorrow morning.