Unpaired female birds use sex to attract already paired males: "La donna è mobile qual piuma al vento"

Pre-existing opinions, assumptions, human hopes and fears were undoubtedly troubled when monogamous birds where first discovered to be unfaithful (GOWATY & KARLIN 1984). Sex is often not exclusive to members of a pair, which shattered the “romantic” picture of several species considered as exclusive mating for their entire life. The “worst” came when we discovered that, in the same way as humans, the birds divorce, cuckold their partner and enjoy a “ménage à trois”. After the first papers published on extra-pair paternity in birds (BRAY et al. 1975, MCKINNEY et al. 1983, ALATALO et al. 1984, GOWATY & KARLIN 1984), followed by papers by WESTNEAT (e.g., 1987, 1988) and the discoveries subsequent to the use of the DNA fingerprinting (e.g., BURKE 1989, BURKE et al. 1989, BIRKHEAD et al. 1990, WESTNEAT et al. 1990), by early 1990 there was no remaining scientific debate: it was considered a novelty a socially and genetically monogamous species ... What disillusionment, when we recall that LACK (1968) considered that monogamy was the mating pattern of 90% of the > 9000 species of birds! These discoveries naturally spurred scientists on to ask themselves how and why the ultimate variety of social monogamy (the pair bond) is maintained for several breeding seasons. Therefore, as if guided by a fervent spirit of moral rehabilitation, scientists undertook a crusade to try to justify the “bad morality” of some species of birds. At that moment, ecology saved both the behaviourists and the new, bad image of birds. When DAVIES (1992) stated, under the influence of the Gowaty extension of the Orians model (ORIANS 1969, GOWATY 1981), that “ecological conditions set the stage on which individuals play out their behavioural strategies”, public opinion “drew a sigh of relief”.