by Matthew Cobb
About 20 months ago we discussed the amazing Peruvian lyre-tailed nightjar, with its fabulous streamer feathers. This morning a rather different, and extraordinary nightjar tailfeather adaptation popped into my inbox, thanks to the Nightjar News email newsletter. It included information about the Standard-winged Nightjar (Caprimulgus longipennis), which sounds kind of… standard, until I realised that by ‘standard’ they mean ‘flag’. Here’s a picture of a male, by Paul Cools.
Those things behind him are his tailfeathers – they are what prompted the species name: longipennis (long feather). Nightjar News explains:
The Standard-winged Nightjar is one of the more impressive members of the Caprimulgid family. This true nightjar species breeds in dry savannah habitat of central Africa. During the breeding season, the male grows highly-specialized wing feathers up to 38 cm long, primarily of bare shaft with feather plumes on the end. The feathers are used as part of a flight display to attract female.
Here’s another picture, from Wikipedia, taken by Jan Steffen:
These long feathers look pretty sexy, and you can see why a gal might like them, but there’s more! Look at how extraordinary they are when he flies (there’s no sound, sadly) – video by Dermot Breen:
Sometimes, the display can look like the bird is followed by two bats:
Here’s another example, from the Gambia – at the end you can hear the male churring:
It seems fairly certain that this is an example of sexual selection – only the male has the feathers, and he has them only during the mating season.
However, this insight is only the beginning of wisdom, for it raises a whole set of questions:
• What exactly does the female see (or maybe hear)?
• Is it simply the length and shape of the feathers she likes, or is there something about the way he does the display that somehow reveals his ‘good genes’ (this is one of the key ideas about how sexual selection works, though in fact we generally know very little about what is ‘good’ about those genes)?
• What exactly is it about the display? Is it ‘supposed’ to look like two birds following him (why?), or is that just an aerodynamic consequence of having those long streamers?
• And here’s the real killer question – how on earth could we find the answers to these hypotheses?
Please chip in below…
[EDIT: On reflection, it seems like there is a difference in the behaviour we can see. In the first video, the male is flying very low, with the ‘standards’ upright, like flags. I wonder if this is a mating flight. In the second video, ‘three birds or one’, he’s flying like a hungry nightjar, with the feathers jiggling along behind him as he does his hunting flight, jinking around trying to catch insects. In the third video, he’s just mooching about and then starts his call… My guess is that the first behaviour is the key one, in terms of sexual selection.]