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.]
Whatever sex selection signals that humans send, they sure are boring compared to the nightjar.
Wow.
I can imagine experiments that record behavior before and after modifying the feathers and seeing how it affects female response. For example, does dying the feathers white make a difference? What if you clip the feathers to make them half the normal size? Etc.
There have been studies of the elongate display feathers in male drongos [one of the African species, I believe] — in one study, tail feathers of some males were shortened by one-half, and some other males were ‘enhanced’ by gluing the distal half harvested from the first half. The study showed that birds with shortened tail feathers were less attractive than control [unaltered] males, while females preferred the ‘super’ males over the controls.
I’d expect similar results with manipulation of other striking secondary sexual characters, including our friend, the nightjar..
That was widowbirds — Malte Andersson from Gothenberg University in Sweden did those landmark experiments, published way back in 1982. It was one of the first manipulative experiments of a sexual signal. Many others have followed; for example, it turns out that removal of the eyespots on peacock tails affects female preference.
Thanks — Funny how memory works — I had this image of a drongo that I couldn’t shake.
You could also make the feathers rigid so they don’t flow naturally.
In the central deserts of AZ we often see Lesser Nighthawk (Chordeiles acutipennis)
feeding along with Mexican free-tailed and western pipistrelle bats. The ‘Three birds or one?’ video is strikingly similar to what Kelly and I view in the evenings minus the long tail feathers but with ‘wingman’ bats hunting with the Nightjar.
I’m curious to know if the bats find some advantage to following or if they just happen to prefer the same route through the air following a cluster of insects.
Me too!
I can’t even begin to think how to answer your set of 4 significant questions — but on the bright side I found the nightjar right away!
Yes! I too spotted the nightjar!!!
😀
Lol!
I trust those are not the bones of unsuccessful nightjars littering the ground in the first pic.
The mating display flight puts me in mind of football fans flying team flags from their pickup trucks on game day.
I love it when a word’s use seems mundane but then one day you say “ahhh, THATS what that means!” This one – standard – is excellent!
It so happens that I learned the origin of the word “feather” today – Old English “fether” from penna (Latin) combined with pteron meaning “wing” (Greek).
Except for their vocalisations nightjars fly silently, but their prey are bugs caught on the wing.
Are those flags silent?
Can we easily test if silent flight is adaptive or not?
Are the males better at catching food out of mating season when they are flagless?
Assuming female sexual preference and male sexual characteristics coevolve, I guess I would like to test it to get some basic insight into the process.
So not knowing anything about this in particular I googled, and I found that there are some ready-made tests out there:
“A new method, ParaFit, has been developed to test the significance of a global hypothesis of coevolution between parasites and their hosts. Individual host-parasite association links can also be tested.”
[ https://academic.oup.com/sysbio/article/51/2/217/1661471 ]
Extraordinary! And I agree that the first video is likely the sexual display.
yes the black longipenis is very sexy
If you strapped-on a prosthetic ornament to a loitering male subspecies, maybe he could get a little extra, albeit unfruitful, consensual interspecies nookie time with the female. The question is: how long will she sit on her unfertilized eggs before she curses her ancestors’ ability to decipher nuance?
I was always assured that size doesn’t matter.
Did I say that out loud?
Here’s the lyre tailed night jar from Peru.
https://www.youtube.com/watch?v=LT3ACCQHIyc
Richard Prum in The Evolution of Beauty proposes that female selection is based on an incidental sense of beauty independent of adaptation. His ideas are disputed.
My first thought upon seeing those long feathers was that they would seem to be a defensive liability for the bird – a predator that might otherwise miss the bird could grab him by those feathers. I have no idea whether nightjars actually have any predators, though.
Reblogged this on The Logical Place.
“Those things behind him are his tailfeathers…”
Actually they’re primaries–wing feathers. Probably why their common name is Standard-winged Nightjar. 😉
Could play havoc with hie flight dynamics,I wonder if anyone has looked into this?
I’d say the effect of these extra “wings” would not be to enhance speed or optimize energy expenditure when getting from place to place. In fact, it undoubtedly slows the bird significantly. During courtship the slowness may actually enhance the effect – meaning the female gets a longer look at the dude’s stuff. The strict adaptionist position might be that the female is judging the males ability to fly in spite of these drag-inducing contraptions. In other words his ability to overcome the handicap means he’s fitter than those that can’t quite handle the maneuvers. Richard Prum’s position, on the other hand, is that the effect it produces are pretty much an accident of the female population’s sense of beauty, which is nonadaptive for anything other than mating.
Here’s the link to Jerry’s post on this subject.
https://whyevolutionistrue.wordpress.com/2017/05/08/an-evolutionary-biologist-misrepresents-sexual-selection/
I’ve never found the handicap theory very persuasive, since it assumes that females consider it a good tradeoff to saddle their sons with a handicap.
If a male with an acquired handicap (an imperfectly healed injury, say) can compete and flourish alongside able-bodied males, then yes, that’s evidence of excellent survival skills, and a female should rightly prefer such a male over his unencumbered brethren (all else being equal), since her sons will not share the handicap and will therefore have a leg up over the competition.
But I’m not seeing why that sensible preference should transfer to males with heritable handicaps. Why not prefer a male who reduces or eliminates the handicap while retaining the traits that compensate for it?
I’m not sure I understand your comment.
If a male with an acquired handicap (an imperfectly healed injury, say) can compete and flourish alongside able-bodied males…
The female choice only comes in when the male traits are visible to her. Most of these measures of vigor would not be visible. A healed injury or a survived bout with disease would not be outwardly visible in most cases.
Males can exhaust themselves jumping about on a log during display. The female could pick up on the fact that his gyrations fade early and decide he doesn’t have enough stamina and would not make a great contribution to the chicks. I suppose. But adding an extra handicap such as a longer tail wouldn’t, I don’t think, make him look strong, but rather weaker.
Put yourself in the place of a female being courted by three different males. Male A has normal, functional tail feathers. Male B has a limp or a broken wing that mildly impedes his movement, but he’s otherwise fit and healthy. Male C has outsize tail feathers that similarly impede his movement but make for an attention-grabbing courtship display.
Which male is likely to contribute most to the adaptive fitness of your children? I claim it’s male B, since he’s managed to survive despite his handicap. Male C has also survived despite his handicap, but will pass that handicap on to his sons, making them on balance no fitter than male A’s sons.
So I see no reason to prefer C over A or B on “good genes” grounds. The only argument for preferring C would be if a preference for flashy courtship displays is already prevalent in the population, making C’s sons likely to father more grandchildren than A’s or B’s sons. But C’s handicap plays no role in that calculus.
I see what you mean. I figured usually the broken wing would either be near fatal and he’d no longer be a serious contender, or it would have completely healed and be invisible. There would likely be some who held the middle ground.
Prum’s idea of female whimsy is appealing as an explanation as far as I can see. The accidental appreciation of subtle exaggerations of small deviations in appearance and performance could, it seems, lead the males to shift the phenotype to some degree against their own survival advantage.
A story inspired by your question…
https://twitter.com/nilou_ataie/status/907816822287691776