When I read Halldor Laxness’s Independent People, it kind of made me want to visit Iceland. On the one hand, it’s a bleakly pessimistic tale of a man struggling to drag himself out of grinding poverty, only to be crushed underfoot by changing circumstances. On the other hand: phalaropes!
Phalaropes — that’s the Red-necked Phalarope — are related to sandpipers, snipes and suchlike. Apart from being rather beautiful, they have a couple of particular quirks of their own. One is this extraordinary feeding behaviour (Red-necked Phalarope again, this time in winter plumage):
That spinning swirls food up to the water surface where they can pick it up — or at least that’s the assumption; it’s not an easy thing to test, and I don’t know if anyone has tried. Whatever the purpose, it is incredibly endearing watching them spin around like little demented rubber duckies.
The other unusual thing about them is that the female is more brightly coloured, while the drabber male incubates the eggs and raises the young. The rule of thumb in biology, that males are larger, more brightly coloured, and more aggressive, arises in the end from a basic physiological bias: sperm are easy and cheap to produce, eggs are more expensive. Babies are more demanding still. So there’s a general advantage for males to try to mate with as many females as possible — they can always make more sperm, so any chance to reproduce is worth a shot — while females have a different set of incentives: because there is a practical upper limit on the number of offspring they can produce, they need to be more choosy their mates. Which is why, in human societies, ‘polygamy’ actually always means ‘polygyny’; men having many wives is common, wives with many husbands incredibly rare.
That logic does apply to birds as well as mammals: birds’ eggs are still somewhat expensive to produce — more so than sperm, anyway — and in the vast majority of birds the males are the ones with the glamorous plumage. But the imbalance is less dramatic, and if the males can be persuaded to sit on the eggs and do all the rearing, that frees up the females to maintain territories, mate with several males, leave eggs with each of them and bugger off leaving them to bring up the chicks.
This role reversal has happened in a handful of bird species, including the phalaropes, the painted snipes, the dotterel, the jacanas (lily-trotters), and the buttonquails. These birds are all somewhat related, but not especially closely; they are in the same large group that includes waders, gulls, terns and auks. Clearly it is a perfectly functional arrangement, but it still leaves you wondering: why them? What circumstance arose that caused this behaviour to switch? Did they go through a period of raising the young cooperatively before the sexual roles diverged again, this time the other way round? It’s fascinating stuff.