Experimental chronic noise exposure affects adult song in zebra finches

Studies over the past decade have revealed many differences in song characteristics between urban and rural populations of passerines. While some of these adjustments are immediate (i.e. flexible responses to a changing acoustic environment), there is evidence that other adjustments may occur over a longer term. We tested whether adult zebra finches, Taeniopygia guttata, would alter their songs after being held in different controlled acoustic environments (one quiet, one with traffic noise) for 5 months and whether these changes would (1) be associated with changes in baseline circulating corticosterone level and (2) persist 2 months after being reacclimated to their original social environment. We found that the noisy environment did not elevate baseline circulating corticosterone. In addition, although noise resulted in song changes, these changes were not consistent with the current hypotheses of acoustic masking and adaptation. Rather, we found that birds living in a noisy environment significantly lowered their minimum frequencies post-treatment, an effect that lasted at least 2 months post-experiment. Furthermore, over the course of the experiment, we found that all birds, regardless of treatment group, increased the duration of their song (by increasing the number of repeated notes within their song) and showed reduced baseline corticosterone. Our results suggest that living in different acoustic environments temporarily may have both immediate and lasting effects on song characteristics. However, because these results do not correspond with field observations of masking avoidance, we suggest that the process of song modification in different environments may be more complicated than initially hypothesized.