The amazing display of the Standard-winged Nightjar

August 1, 2017 • 12:00 pm

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.

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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:

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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.]

Spot the Nilgiri Marten!

September 21, 2015 • 1:57 pm

by Matthew Cobb

Aditya Gangadharan (aka @AdityaGangadh) posted this pic on Twitter. To give you a hint, a Marten is a mustelid (methinks it is like a weasel), about 50 cm long, with a tail that is slightly shorter. So we ain’t talking nightjars! Click twice to embiggen sans book adverts, comme d’hab’.

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Wikipedia claims:

Very little is known about the Nilgiri marten. It is diurnal, and though arboreal, descends to the ground occasionally. It is reported to prey on birds, small mammals and insects such as cicadas.

I was partly attracted to this photo because the Nilgiri Marten is found in the Nilgiri hills in south-western India. For several years, together with ant-expert Christian Peeters, I worked on a population of ant from this region, called Diacamma. Diacamma ants are queenless – they have lost the queen caste, and one worker dominates the others. She is called a gamergate (pronounced gammergate – the word means, or perhaps meant, given that there’s now another meaning, ‘married worker’) and lacks the large ovaries and wings typical of queens.

This situation is typical of many Ponerine ants, but what is weird about Diacamma is that they possess external glands called gemmae – apparently based on wings – that enable them to produce pheromones and to mate. The dominant female hangs around the cocoons waiting for the new ants to hatch out, and she then bites off their gemmae, effectively sterilising her sisters (and later, her daughters). (We studied how this takes place – contact me if you want a copy of the article, as the full article is behind a paywall.)

When the gamergate dies, or the colony splits and half the colony no longer has a gamergate, the first female to hatch out is not mutilated (there’s no one there to do it), so she becomes the new dominant. For pictures of the gemmae go here.

This situation exists in all Diacamma ants, except the Nilgiri population, where no mutilation takes place and the gamergate imposes her dominance physically, as in other Ponerines. This group is not a separate species from the local D. ceylonense, as the two taxa will interbreed (we succeeded in doing this in the lab – a big deal if you work on ants). You can read an abstract from a recent paper by Christian Peeters here.

The scrappy ground seen in the photo is the kind of place you get Diacamma ants – there might even be some mooching around…