Birds
Ruff
Calidris pugnax · also called ruff, reeve
The ruff is a medium-sized wading bird, and for most of the year it is an unremarkable brown sandpiper. But it has become a star of evolutionary biology because of its males, which come in three fixed, lifelong types — territorial fighters, pale-collared hangers-on, and a rare form that disguises itself as a female — all determined by a single block of genes inherited as a unit.
Overview
The ruff breeds across the wet tundra and marshes of northern Eurasia and winters in Africa, the Middle East, and South Asia. Males (29–32 cm) are much larger than females (22–26 cm). In spring, breeding males grow an enormous ruff of neck feathers and head tufts; the rest of the year both sexes are plain and scaly-brown. The female is called a reeve.
Three kinds of male
- Independents (about 5 in 6) are dark-ruffed, hold and defend small courts on a lek, and their ornaments vary hugely in colour between individuals.
- Satellites (about 1 in 6) have pale ruffs, hold no territory, and are tolerated on an independent’s court because they draw in females; they steal occasional matings.
- Female-mimics (“faeders,” about 1 in 100) grow no ruff and look like females, slip onto the lek unchallenged, and sneak matings — supported by unusually large testes.
One supergene
The three forms are set by a single large block of genes, inherited as a unit because a chromosome inversion stops it being broken up. It arose about four million years ago — the faeder version first, then the satellite version by a rare genetic reshuffle.
Status
The ruff is Least Concern globally but declining, and has been lost as a breeder from much of western Europe as wet meadows were drained and intensified.
Ruff: common questions
Why does the ruff have three kinds of male?
Each form is a different strategy for getting matings, and all three can succeed. Independent males compete directly, winning by holding the best spot on a lek and driving off rivals, which works if you are large and can fight. Satellite males avoid the fighting; they act as junior partners on an independent's court, and because females prefer courts with more males on them, both benefit, and the satellite picks up some matings. Female-mimics bypass competition entirely by looking like a female and mating on the sly. Because females are drawn to busy, varied leks, a mix of all three types persists in the population rather than one winning out.
What is a supergene, and how does it control the ruff's forms?
A supergene is a cluster of genes that sit close together on a chromosome and are inherited together as a single block, because a structural change in the chromosome, an inversion, stops them from being separated by the normal shuffling of genes. In the ruff, one such block determines which of the three male forms a bird develops, affecting body size, plumage, hormone levels, and behaviour all at once. The independent form carries the ancestral version of the block; the female-mimic and satellite forms carry rearranged versions. Because the block cannot be broken up, the three packages of traits stay intact down the generations.
Are female-mimic ruffs actually females?
No, they are genetic males that develop a female-like appearance and are fully capable of fathering chicks. A faeder is roughly the size of a female, lacks the breeding male's ruff and head tufts, and has female-type back plumage, so on a lek the territorial males do not treat it as a threat. It uses that cover to approach displaying females and mate with them opportunistically. To support this sneaky strategy it invests heavily in sperm production, and faeders have the largest testes relative to body size of the three male forms.
Why has the ruff disappeared from so much of western Europe?
The ruff breeds in wet, open grassland and marsh, and that habitat has been transformed across lowland western Europe. Wet meadows have been drained, levelled, reseeded, fertilised, and mown or grazed earlier and harder, which destroys nests, removes the insect food chicks need, and makes the ground unsuitable for the birds' displays. Populations in the Netherlands, Germany, Britain, and elsewhere have dwindled or vanished as breeders, and the species now nests mainly in the vast, less-disturbed wetlands of Scandinavia and Arctic Russia, passing through the west only on migration.