Tyrant flycatchers are the largest New World bird family and no wonder, considering the amazing diversity of insect species on which they can feed. In addition, many of Costa Rica’s 78 species also eat small fruits and berries.
With or without documentary photographic evidence, I find it’s sometimes hard to be sure what that small flycatcher is/was. I say ‘was’, because, yet again, a flycatcher sighting this week makes me call into question past sightings. In this particular case, I am now even questioning identifications made by experts in the field, with bird in hand!
No question, however, about the identity of the Paltry Tyrannulet (formerly Mistletoe Tyrannulet) (Zimmerius vilissimus) photographed, above, by Richard Garrigues. This is the one and only small flycatcher in my garden here in San Antonio that I can (almost) always identify. It’s much the commonest of the ones with confusing plumage and it does love to eat mistletoe. It’s fairly short, rather sad whistle is another good aid in identifying it.
My current doubts pertain, however, to the differences between the Yellow-olive Flycatcher (Tolomyias sulphurescens) and the Yellow-margined Flycatcher (Tolomyias assimilis), which are presented on pages 194-5 of Garrigues and Dean’s first edition (I do not yet possess the brand-new, second edition). The other day I found one of the two inside the crown of a tree of about twenty feet in height in an area where I have previously made what I thought were sure identifications of the two. The usual identification problem here is because the eye colour is supposedly the only certain distinction.
Unfortunately, this new sighting seemed to have a red iris, which causes me to look at the Rough-legged Tyrannulet (previously Zeledon’s Tyrannulet) (Phyllomyias burmeisteri) pages 190-1. I did not note wing-bars, however. The bird did not call and I have not found it on subsequent days. The tyrannulet would be a rare sighting, even though our area is within its Costa Rican range, while my first inclination with earlier sightings has always been towards the Yellow-olive Flycatcher, which is described as common and widespread up to 1400 m. The Yellow-margined Flycatcher is ‘fairly uncommon’ and tends to be found below 1000 m.
I scanned numerous photos of all three species on the internet and found it impossible to separate properly on the basis of photographs that purportedly made clear identifications.
I welcome any comments or hints from interested bird watchers with experience in the field here in Costa Rica.