One hypothesis for duetting is the joint territory defense hypothesis which suggests that birds use duets so that the pair can defend their territory against rivals of the same species. Another hypothesis is mate-guarding in which a member of the pair duets in order to keep same-sex rivals away from their mate. A third hypothesis is the acoustic contact hypothesis. This hypothesizes that birds use duets to remain aware of their mating partners in areas where visual contact might not be feasible, for example in a habitat that is very dense (Mennill, …show more content…
Bird pairs duet to protect their territory as a duetting pair is seen as more threatening to a rival than a solo bird (Dahlin, 2012). In a study of Rufous and white wrens, it was shown that pairs increased the amount of their duetting about five times when confronted with an intruder compared to their baseline duetting behavior – from 1.2 to 6.8 duet calls. They also performed their duets significantly closer to each other in provoked settings compared to unprovoked settings. (Mennill, 2008). These cooperative efforts of rufous and white wrens support the territory defense hypothesis. In yellow-naped amazons, duetting was researched using playback methods. They hypothesized that if the birds were using duetting for territory defense, the pairs would act in coordination with one another. If the birds were using duetting for mate-guarding, the pair would not act in coordination; instead, there would be differences between male and female responses particularly a stronger response to same-sex solos. The data on the playback experiment supported the first hypothesis more closely. There were no statistically significant response differences between males and females, and both sexes moved closer to the speaker and participated in more growls compared to pre-playback. Both sexes of yellow-naped amazons reacted to the