Dusky-faced Tanager confirmed, but what are these antbirds?

I have immense respect for the birdwatchers monitoring the sightings that I and many others send to Cornell University’s eBird database. If you enter a sighting that their experts consider rare, the following message appears:

This bird is rare for this date & location, please add comments and check ‘Complete’. 

When this pops up I always have to ask myself if I am absolutely sure of the identification. I keep detailed lists of sightings, especially for my local area, because I firmly believe that this is our major source of knowledge regarding species distribution. I can contribute in an area that does not have much coverage from other birders. EBird’s warning message came up with my entry a few days ago for the Dusky-faced Tanager (Mitrospingus cassinii), a fairly common Caribbean lowlands bird usually occurring only up to an elevation of around 600 m. I had found at least 2 birds just above the San Diego waterfall on Quebrada La Loca, but now I had to review my findings.

"Dusky-faced Tanager (Mitrospingus cassinii)" - by Dominic Sherony [CC BY-SA 2.0], via Wikimedia Commons

“Dusky-faced Tanager (Mitrospingus cassinii)” – by Dominic Sherony [CC BY-SA 2.0], via Wikimedia Commons

I was sure of the main field marks, but are there other candidates that might have confused me? After looking at the literature, it seems to me that there is really just one possibility, Carmiol’s Tanager (Chlorothraupis carmioli), formerly known as the Olive Tanager. Carmiol’s has quite a few Turrialba area sightings recorded on eBird, while the Dusky-faced does not. This makes me very suspicious, especially since I do not know either of these species well. Carmiol’s habits are similar to those of the Dusky-faced and it is found up to elevations of 1000 m, which is more or less the elevation of San Diego. However, Carmiol’s has no contrasts in its plumage and it lacks the staring white iris on a dark face of the Dusky-faced. It also has a typical tanager bill, where the Dusky-faced has a pointy bill like that of an oriole. Happily, I was able to note all these field marks. I also listened carefully to sound recordings of both species and there is no possible confusion there.

Happily again, among the first birds in the forest today was a flock of at least 4 of said Dusky-faced. I noted the same characteristics and the same voice as before; unfortunately friend Chalo, carrying an excellent camera, could not get a photograph. Nonetheless, I consider the identification well confirmed! Nonetheless, I shall return tomorrow to make doubly sure.

I love Costa Rica. Here, barely one kilometer from my house, I can still find exciting bird habitat that I have barely explored in my more than eight years of residence. Today was another red-letter day as I confirmed yet another life bird, the Three-striped Warbler (Basileuterus tristriatus), and spent two hours in a beautiful environment full of North American migrants and resident species.

The Summer Tanager, a common migrant in this area, is now here in numbers, but I was surprised to find two black-winged Scarlet Tanagers (Piranga olivacea), one a non-breeding male and one a female, in a clearing on the path. Perhaps I shouldn’t be surprised, since my last sighting of this species was in October of 2014, also at San Diego!

Warblers were numerous, as were tanagers and flycatchers, though many of the latter eluded identification among so much foliage. The following list pertains only to species seen on the forest path that leads to the waterfall, note all the question marks!

  1. Squirrel Cuckoo
  2. Red-faced Spinetail?
  3. Dusky Antbird/Slaty Antwren?
  4. Slaty-capped Flycatcher
  5. Olive-sided Flycatcher
  6. Contopus sp.
  7. Stripe-breasted Wren
  8. Swainson’s Thrush
  9. Golden-winged Warbler
  10. Chestnut-sided Warbler
  11. Blackburnian Warbler
  12. Canada Warbler
  13. Three-striped Warbler
  14. Dusky-faced Tanager
  15. Summer Tanager
  16. Scarlet Tanager
  17. Bay-headed Tanager
  18. Silver-throated Tanager
  19. Euphonia sp.

Next day’s follow-up hike was another big success for me, although I again missed more species than I was able to clearly identify. The Dusky-faced Tanagers again trooped faithfully by, twice, once on the way down to the waterfall and once on the way back up. They seem easy to find here, though there were only three of them this time, as far as I could tell.

The antbird/antwren problem again appeared, but this time the all-black little bird seemed to have a fairly big splash of white on the wing. This means that a third species, the Dot-winged Antwren (Microrhopias quixensis), and a fourth, the White-flanked Antwren (Myrmotherula axillaris), come into the picture. They, together with my first suspicion, the Slaty Antwren (Myrmotherula schisticolor), are on pp. 220-221 of Garrigues and Dean’s The Birds of Costa Rica. The males of all of these are black with some white in the wing, but I was unable to find a female, which would be helpful with the Dot-winged at least!

Or is it the not-quite-so-dark Dusky Antbird (Cercomacra tyrannina), pp. 214-215?  My money is on the Dot-winged Antwren because of the prominent white on the wind that I thought I saw, and also because I distinctly saw that the shape of the tail was what Stiles & Skutch describe as ‘graduated’. We’re assuming, of course, that on all three visits so far I have been seeing just one species. I have a lot of work to do, but what fun!

Here’s a pic by friend Karel Straatman, taken here in Costa Rica, that gives an idea of the problem. Karel was told by an accompanying guide or birder that it was either a Dusky Antbird or a Slaty Antwren. No one has been able to make a certain identification of the bird in this photograph:

Male Dusky Antbird or male Slaty Antwren? What do you think?

Male Dusky Antbird or male Slaty Antwren? What do you think? (photo courtesy of Karel Straatman)

And this one?

Another suspected Antbird, we assume a female. Any ideas?

Another suspected Antbird, we assume a female. Any ideas? (photo courtesy of Karel Straatman)

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