Assortative pairing based on contact call similarity in budgerigars, Melopsittacus undulatus

Abstract

A trait typical of parrots, but rare in other groups of birds, is the acquisition of new learned calls (acquired by copying conspecifics) throughout an individual's lifetime. The significance of this distinctive psittacid trait is not understood. In budgerigars, females preferentially affiliate with unfamiliar males whose contact calls resemble their own during brief dyadic choice trials; also, in forced-pair situations, contact call similarity of members of pairs increases as a result of a male tendency to imitate his mate's call type. The functions of budgerigar call imitation and preference for pre-pairing similarity are currently unknown. Moreover, as budgerigar pair formation occurs over a span of days or weeks, it is important to determine whether birds in breeding colonies assort and proceed to breed on the basis of pre-pairing contact call similarity, and whether high levels of call similarity are maintained after pair formation is complete. To explore these questions, we recorded contact calls of male and female budgerigars before and after they were placed into an aviary equipped for breeding. As predicted, birds paired assortatively based on pre-pairing call similarity. Once birds had paired, their calls converged further in acoustic structure, as previous work had led us to expect. However, after eggs were laid and the males began to feed their mates, the calls of mated birds diverged, suggesting that there might be some cost to maintenance of shared calls. Male care-giving correlated with the degree to which his pre-pairing calls resembled those of his mate, but not with the similarity achieved through convergence. These results suggest that female budgerigars may use a male's pre-pairing call similarity as a predictor of paternal investment. The questions of why such similarity predicts male care-giving, and why calls converge following initial pairing activities, require further work. © 2006 The Authors.