This species shows marked sexual dimorphism; the male is much larger than the female (the reeve), and has a breeding plumage that includes brightly coloured head tufts, bare orange facial skin, extensive black on the breast, and the large collar of ornamental feathers that inspired this bird's English name.

Three differently plumaged types of male, including a rare form that mimics the female, use a variety of strategies to obtain mating opportunities at a lek, and the colourful head and neck feathers are erected as part of the elaborate main courting display.

Predators of wader chicks and eggs include mammals such as foxes, feral cats and stoats, and birds such as large gulls, corvids and skuas.

[12] In the May-to-June breeding season, the male's legs, bill and warty bare facial skin are orange, and he has distinctive head tufts and a neck ruff.

[3] The plumage of the juvenile ruff resembles the non-breeding adult, but has upperparts with a neat, scale-like pattern with dark feather centres, and a strong buff tinge to the underparts.

[10] Adult male ruffs start to moult into the main display plumage before their return to the breeding areas, and the proportion of birds with head and neck decorations gradually increases through the spring.

They have a lower body mass and a slower weight increase than full adults, and perhaps the demands made on their energy reserves during the migration flight are the main reason of the delayed moult.

Before developing the full display finery with coloured ruff and tufts, the males replace part of their winter plumage with striped feathers.

The striped prenuptial plumages may represent the original breeding appearance of this species, the male's showy nuptial feathers evolving later under strong sexual selection pressures.

[3] It avoids barren tundra and areas badly affected by severe weather, preferring hummocky marshes and deltas with shallow water.

[20] A Hungarian study showed that moderately intensive grazing of grassland, with more than one cow per hectare (2.5 acres), was found to attract more nesting pairs.

[3] A minority winter further east to Burma, south China,[3] New Guinea and scattered parts of southern Australia,[24] or on the Atlantic and Mediterranean coasts of Europe.

[16] Many migratory species use this differential wintering strategy, since it reduces feeding competition between the sexes and enables territorial males to reach the breeding grounds as early as possible, improving their chances of successful mating.

They perform an elaborate display that includes wing fluttering, jumping, standing upright, crouching with ruff erect, or lunging at rivals.

Satellite males do not have to expend energy to defend a territory, and can spend more time foraging, so they do not need to be as bulky as the residents; indeed, since they fly more, there would be a physiological cost to additional weight.

Males switched between the three tactics, being more likely to attend a lek when the copulation rate the previous day was high or when fewer females were available after nesting had started.

[47][48] The scientists were able to show that the first genetic change happened 3.8 million years ago on the resident chromosome, when a part of it broke off and was reintroduced in the wrong direction.

The inactivation of the gene has severe deleterious effects and pedigree data of a captive ruff colony suggests that the inversion is homozygous lethal.

Two of these deletions remove evolutionary highly conserved elements close to two genes- HSD17B2 and SDR42E1-both holding important roles in metabolism of steroid hormones.

The authors conclude that one or more of the deletions act as a cis-acting regulatory mutation which is altering the expression of one or both genes and eventually contributes to the different male phenotypes and behaviour.

[12] The precocial chicks have buff and chestnut down, streaked and barred with black, and frosted with white;[49] they feed themselves on a variety of small invertebrates, but are brooded by the female.

[50] Adults seem to show little evidence of external parasites,[56] but may have significant levels of disease on their tropical wintering grounds,[57] including avian malaria in their inland freshwater habitats,[57] and so they might be expected to invest strongly in their immune systems;[58] however, a 2006 study that analysed the blood of migrating ruffs intercepted in Friesland showed that this bird actually has unexplained low levels of immune responses on at least one measure of resistance.

[12] The ruff normally feeds using a steady walk and pecking action, selecting food items by sight, but it will also wade deeply and submerge its head.

On migration and during the winter, the ruff eats insects (including caddis flies, water-beetles, mayflies and grasshoppers), crustaceans, spiders, molluscs, worms, frogs, small fish, and also the seeds of rice and other cereals, sedges, grasses and aquatic plants.

This is thought to be because the godwit cannot use refuelling areas to feed on its trans-Pacific flight, whereas the ruff is able to make regular stops and take in food during overland migration.

[9][66] ...if expedition is required, sugar is added, which will make them in a fortnight's time a lump of fat: they then sell for two Shillings or half-a-crown a piece… The method of killing them is by cutting off their head with a pair of scissars [sic], the quantity of blood that issues is very great, considering the size of the bird.

[66] The heavy toll on breeding birds, together with loss of habitat through drainage and collection by nineteenth-century trophy hunters and egg collectors, meant that the species became almost extinct in England by the 1880s, although recolonisation in small numbers has occurred since 1963.

[72] Although this bird eats rice on the wintering grounds, where it can make up nearly 40% of its diet, it takes mainly waste and residues from cropping and threshing, not harvestable grain.

It has sometimes been viewed as a pest, but the deeper water and presence of invertebrate prey in the economically important early winter period means that the wader has little effect on crop yield.

[21] The ruff is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies, where it is allocated to category 2c; that is, the populations in need of special attention as they are showing "significant long-term decline" in much of its range.