A lek is an aggregation of males gathered to engage in competitive displays, lekking, that may entice visiting females who are surveying prospective partners for copulation. Leks are commonly formed before or during the breeding season. A lekking species is characterised by male displays, strong female mate choice, and the conferring of male indirect benefits. Although lekking is most prevalent among avian species, lekking behavior is found in insects, amphibians, and mammals as well.
The term derives from the Swedish lek, a noun which typically denotes pleasurable and less rule-bound games and activities ("play", as by children). English use of lek dates to the 1860s. Llewelyn Lloyd's The Game birds and wild fowl of Sweden and Norway (1867) introduces it (capitalised and in single quotes, as 'Lek') explicitly as a Swedish term.
The term was originally used most commonly for black grouse (Swedish: "orrlek") and for capercaillie (Swedish: "tjäderlek"), and lekking behavior is quite common in birds of this type, such as sage grouse, prairie chicken, great bustard and sharp-tailed grouse. However, lekking is also found in birds of other families, such as the ruff, great snipe, Guianan cock-of-the-rock, musk ducks, hermit hummingbirds, manakins, birds-of-paradise, screaming pihas and the kakapo. Lekking is seen in some mammals such as the Ugandan kob (a waterbuck), some pinnipeds, several species of fruit bat, and the topi antelope. Lekking is found in marine iguanas and some species of fish (e.g., Atlantic cod, desert pupfish, and the cichlid Astatotilapia burtoni). Even insects like the midge and the ghost moth demonstrate lekking behavior. Lekking is also found in some paper wasp species such as Polistes dominula, the orchid bee Eulaema meriana, in some butterfly species like the black swallowtail (Papilio polyxenes), and in tarantula hawks like Hemipepsis ustulata.