On the morning of October 19, 2009 I was at Bentsen State Park/WBC in the Lower Rio Grande Valley of south Texas, principally to look for odonates. From about 9.30am onwards large numbers of "thermalling" birds started to take advantage of excellent migration conditions (a steady SE breeze; a few scattered clouds). Mostly it involved Broad-winged Hawks (1,000+), many of which must have overnighted not too far north of the park. Increasing numbers of Turkey Vultures were also moving, along with a small number of Swainson's, Cooper's and Sharp-shinned Hawks and a couple of harriers and falcons, plus six rather late Wood Storks. At 10.50am I was at the boat ramp overlooking the resaca when I spotted a low-flying Cooper's Hawk circling over the woodland adjacent to the resaca, looking for rising air. Almost immediately I also noted a smaller bird above it, also circling in soar-mode but with more bouts of flapping - and that flapping looked suspiciously like a nightjar! Through binoculars I quickly saw that it had very blunt wingtips, a longish-looking unforked tail, and large white crescents at the base of the dark primaries. I got my camera out and tried to get photos - not very successfully as you'll see below - and they seem to confirm that this was indeed a "wing-banded" nightjar - of which the only likely candidate is Pauraque.
The nighjar and the Coop circled around, with the Coop lower, as they drifted south and westwards, away from me, searching for rising air. Finally I lost sight of them both in the glare of a bright sky. The Coop hardly flapped at all during the period of observation, whereas the nightjar flapped more than it soared, but did soar a few times for a number of seconds at a time. In the field I saw no real details of the underside, as I was concentrating on trying to focus my camera. I am rather surprised to see that some of the images suggest areas of very pale (or white) on the underparts...?
This event made me realise that I had no real idea of the migration mechanism employed by the migratory nightjars (e.g. Chuck, Whip). I have always presumed them to be nocturnal direct-flight migrants, as are most migratory woodland landbirds, but I've struggled to find any definitive statements in this area. One online site about migration says that nightjars are normally solitary night-flying migrants, but may also move nocturnally in small groups. So, are there documented occurrences of these phenomena?: daytime nightjar migration?; thermalling by nightjars (as opposed to nighthawks)?; observed migration of Pauraque? :
The first three images are wide-crops to show context and the Coop - each contains a zoomed-in view of the nightjar:
Note in pic above plus in two of the three zooms below that large parts of the underside (body; underwing coverts) appear to be whitish(?):