Immune system activation affects song and territorial defense

Previous studies have demonstrated that bird song is influenced by infection. We investigated how mounting an immune response by mountain white-crowned sparrows (Zonotrichia leucophrys oriantha) affects specific aspects of territorial song and behavior. We used song playback to simulate a territorial intrusion and elicit baseline song and behavioral responses. Individuals were then either injected with a saline control or with a lipopolysaccharide (LPS) solution to induce an acute immune response, and posttreatment territorial song and behaviors in response to playback were recorded 1 day and 7 days later. The immune challenge significantly reduced the number of birds that sang compared with control individuals on Day 1. All birds that sang on Day 1 produced abnormal songs with fewer terminal notes, exhibited elevated alarm behavior, and tended to sing at slower rates. By Day 7, LPS treatment had no effect on the likelihood of singing, and song rates had returned to baseline levels, though songs were still sung with fewer terminal notes. Thus, our study shows that simply mounting an immune response to infection, as opposed to the actual infection per se is sufficient to impact avian song production. This study also suggests that for the most sensitive assessment of immune status, familiarity with an individual's song and behavior is necessary.