Monogamy on the fast track

Abstract

Social monogamy has evolved multiple times and is particularly common in birds. It is not well understood why some of these species are continuously and permanently paired while others occasionally 'divorce' (switch partners). Although several hypotheses have been considered, experimental tests are uncommon. Estrildid finches are thought to be permanently paired because being short-lived opportunistic breeders, they cannot afford the time to form a new pair relationship. Here it is shown through a controlled experimental manipulation that zebra finches (Taeniopygia guttata) allowed to remain with their partners to breed again are faster to initiate a clutch (by approx. 3 days) than birds separated from their mates that have to re-pair, supporting the hypothesis that continuous pairing speeds up initiation of reproduction, a benefit of long-term monogamy in a small, short-lived, gregarious species.

Figure 1

Clutch initiation latencies (untransformed, means±s.e.m.) before (phase 1) and after (phase 2) assignment to groups. Day 0 was the day the pairs were moved to pair cages for daily nest checks (latencies from the beginning of the aviary period would be 5 days longer). The group×phase interaction was significant (means±s.e.m.; p=0.018).

Figure 2

Distributions of phase 2 clutch initiation latencies (untransformed) for (a) Same Partner and (b) Different Partner pairs. Arrows indicate means. Latencies in (a) were significantly shorter (p=0.0025).