Yucatan and Cozumel, Mexico November 2013
From November 16 - 24, 2013, Sheridan Coffey, Dan Peak and I visited the Yucatan Peninsula of Mexico, birding at Cozumel, Felipe Carillo Puerto, Calakmul, Chichen Itza, Rio Lagartos, and Coba.
At around 8am on November 23, 2013 we arrived at the lake at the Coba Archeological Site. In the parking area to visit the ruins was a large tree that must have been producing a large hatch of insects, since there was a swirling mass (200+) of feeding creatures very low over the crown. They were so tightly-packed and fast that for a second or two we thought they were bats - but a quick look revealed that they were Chaetura swifts.
The only Chaetura that is supposed to be in this area in late November is the resident Vaux's (Yucatan) Swift C. vauxi gaumeri (migrant Chimney Swifts C. pelagica having passed though by this date). From what I can gather, this is a poorly-known taxon that could be considered specifically distinct from nominate vauxi and/or the nearest population in the vauxi group, tamaulipensis. This latter taxon is described as being a bit smaller than vauxi and notably darker below, being closer to pelagica in terms of general underbody darkness and contrast with a paler throat (but apparently the lighter area extends further onto the chest than is typical of pelagica). In turn gaumeri is described as being smaller again than tamaulipensis, with relatively shorter tail and wings.
Click here to go to a page of specimens examining Sick's Swift C. meridionalis and comparing it to pelagica and vauxi (and other Neotropical taxa that could possibly occur in the U.S.). About 2/3rds of the way down this page are photos showing one each of C. v. tamaulipensis, gaumeri, richmondi, and nominate vauxi; from this limited comparison it appears that gaumeri is significantly smaller than the other taxa.
I present here twenty-six photos taken during this feeding event; I cannot vouch that all are of different individuals, but surely most are. NOTE: these photos were taken in early morning light creating a dramatic difference in lighting, depending on whether the bird is in shadow or in sunlight, or which direction the bird is facing relative to the sun. The images are cropped originals - i.e. there has been no post-exposure editing.
Also here is a link to a video I shot, showing the feeding and with audio of their calls.