Self-defeating Bowerbirds

BChlamydera_nuchalis_by_Bowdler_Sharpeowerbirds are famous for the method the males use to attract mates. They construct a sort of archway from grasses and what is called a court out of stones, bones and brightly coloured objects. When a female comes past the male puts on a display for her in the bower, waving various objects around in a way she sometimes finds impressive enough to decide that this is a suitable father for her children.

Or perhaps I should say “sperm donor” since the male does absolutely nothing to raise the young. Instead the female goes off to construct her own nest and lay her eggs while the male goes back to tending his bower. It is thought the system exists because males with the time and commitment to produce an impressive bower are more likely to be healthy and active and pass these genes on to the next generation, even though the male refuses to put his construction skills to the task of raising or protecting the young.

Earlier this year ecologists from Deakin University published a paper noting a remarkable thing about the largest species, the great bowerbird. These birds arrange their courts to create an optical illusion. They place the smaller objects towards the direction from which the female will be observing, and steadily larger objects behind. It’s not obvious why they do this, but it works; not all males are able to construct the illusion equally successfully, and those that are good at it have a better success record in winning females. Indeed it seems this illusion is particularly important – while other bowerbirds use lots of bright colours, the great bowerbird, native to northern Australia, uses only occasional hints of red or green, relying on the patterning instead.

So far, so good. But the team took it further. In recent paper in the Proceedings of the National Academy of Sciences they revealed what happened when they tried to give the poorer performers a hand. The scientists moved some of the objects in the court around, creating a far more deceptive illusion. They wondered whether the birds would take the hint and rise to a higher standard, or whether the effective pattern would slowly decay as new objects were added.

As it turned out, neither occurred. Instead the males promptly set about restoring their old, unsuccessful, bower. Perhaps if the birds simply had a form of OCD that required every object to be put back in the original spot some sympathy might be in order, but this was not the case. “They were completely uninterested in right versus left locations, but insisted on putting things back in the same area in terms of forward and back,” co-author Professor John Endler told me.

Moreover, the male birds spent almost three days restoring their old, failing, bower with only occasional foraging missions for trivial things like food. Then again, bowerbirds will keep some of the same items for up to 20 years, carrying them to new bower locations as they move each breeding season, so three days may seem a small investment.

It’s a bit like if Queer Eye For The Straight Guy dropped round to give an edge to some bloke with a truly awful strike rate, and as soon as they were gone he threw out all the elegant furnishings and brought back the discarded pizza boxes, even without buying new pizzas to eat. Unsurprisingly, the males did no better afterwards than before.

The particularly remarkable thing about this is that bowerbirds are related to crows, birds so astonishingly good at learning they have forced a major rethink of animal intelligence. Indeed the creation of what is known as “extended phenotypes” such as these bowers require certain cognition skills, thought to be another reason why males with the best bowers are more likely to sire successful offspring.

Endler says he has absolutely no idea of the evolutionary basis for this behaviour, although that is perhaps not surprising since he also doesn’t know what the point of the optical illusion might be in the first place. However he wonders if it might not throw light on the question of dishonest displays, for example where males produce a mating call that suggests they are larger than they really are, or a deceptively dangerous looking weapon. Such things exist (I’ve done stories on them amongst certain crabs) but they are surprisingly rare.

Endler told me he wasn’t aware of something similar in any other animal, although the paper (which I only read afterwards) refers to what may be similar behaviour in African cichlids. Then again in most cases it would not really be practical to test. It’s not as though some researcher could come and equip a peacock with a more brightly coloured tail, only to have him shake it off, nor are crabs fitted with extra-large prosthetic limbs to see if they prefer these when it comes to impressing the ladies. There must be one animal however who occasionally behaves in such self-destructive behaviour. Think hard.

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About Stephen Luntz

I am a science journalist, specialising in Australian and New Zealand research across all fields of science. My book, Forensics, Fossils and Fruitbats: A Field Guide to Australian Scientists is out now through CSIRO Publishing. I am also a professional returning officer for non-government organisations. I'm very politically active, but generally try to restrict this blog to scientific matters.
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2 Responses to Self-defeating Bowerbirds

  1. Pingback: Humans have sex to keep the species healthy | My Treatise

  2. Pingback: How Sex Keeps The Species Healthy | MKT Library

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