Originally Posted by Nutcracker
I'd suspect predation risks might also be significant for keeping Nightjars nocturnal - they are slower fliers than Nighthawks, so easier for a raptor to catch in good light. I remember reading that predation risk is the major driver for keeping bats nocturnal; day-flying bats don't have good life chances, and the same could apply to Nightjars.
Yes Nutty thanks, Nightjars would appear to be less “speedy” than Nighthawks due to evolved shape and size, which may well explain their would be vulnerability during any diurnal movements albeit as John points out below, there may well be exceptions to this behaviour when needs must, perhaps taking advantage of weather conditions particularly when migrating?
Originally Posted by Farnboro John
Acknowledging the force of all that has been said, I saw my first migrating Nightjar come in-off at Selsey Bill this spring, which was very nice and in broad daylight. At the speed it was going I suspect it had set off over the Channel in daylight though that doesn't mean it hadn't flown all night.
I envy you that experience John must have been a sight to behold. Circa ten years ago I was hunting Woodcock (with bins) post sunset in a local area, when I heard what I initially (at distance) thought was an old motorbike, which then morphed into a “faint” churring followed by the manifestation itself! just a few metres ahead of me in total silhouette. I can say to this day that being so close and able to appreciate the “buoyancy of flight” was mesmerising and left me thinking of how it might have looked in broad daylight.
It might be of interest reading from Birds of Cyprus (David and Mary Bannerman) an extract written April 30th 1954 driving Eastwards at night along the high road between Lefkoniko and Kantara a distance of twelve miles, they counted sixty eight individuals (of which half were males), I suppose that might be called a” loose flock” or “social distancing”, wonder if those numbers could be relied upon today?