Teenage love: the importance of trial liaisons, subadult plumage and early pairing in barnacle geese

In long-lived, socially monogamous species with biparental care, careful selection of a suitable breeding partner can be expected to enhance reproductive success. Both sexes are therefore expected to be choosy and to sample a number of potential mates before making a final choice. We investigated mate-sampling behaviour in 1-year-old barnacle geese, Branta leucopsis, upon their first return to the natal colony. Barnacle geese sampled mates by forming trial liaisons with a number of potential partners before final pair formation, at 2-3 years of age. Heavy 1-year-old females were more likely to engage in trial liaisons than other females, One-year-old males that engaged in trial liaisons, on the other hand, had more adult-like plumage, but did not differ in any other respect from 1-year-old males that were often alone. In addition, male trial partners of 1-year-old females were often older than 1 year. Differences in plumage characteristics between 1-year-old males reflected differences in social status. The observed patterns are suggestive of preferences for certain types of trial partners, where males and females differ in the characters they value most in a potential mate. However, intrasexual competition could also play a role. Birds benefited directly from engaging in trial liaisons at an early age because of reduced aggression from older birds when they were in the company of a trial partner. There were also long-term benefits of engaging in trial liaisons. Females that were often in the company of older trial partners enjoyed higher reproductive success later in life. This was not because they were larger and heavier than females that were mostly alone or with 1-year-old trial partners. Finally, both males and females that found their final partner early in life had a lower age at first reproduction. (C) 2001 The Association for the Study of Animal Behaviour.