Blue whale vocal behavior is affected by man-made noise, even when that noise does not overlap the frequencies the whales use for communication, according to new research published Feb. 29 in the open access journal PLoS ONE. The whales were less likely to emit calls when mid-frequency sonar from ships was present, but were more likely to do so when ship sounds were nearby, the researchers report. The data show an acoustical response from blue whales to MFA sonar and ship noise. In particular, there is a disruption of the D call production of these animals with MFA sonar. The implications of such a response are unknown to date, but owing to the low received level, a single source of MFA sonar may be capable of affecting the animals’ vocal behavior over a substantial area. Additionally, nearby ships elicit more intense D calling by blue whales.