Many animals respond to increases in ambient noise with increases in call amplitude, shifts in frequency, or changes in cue rate, known as the “Lombard effect.” Humpback whales are highly acoustically active and vocalizations include non-song “social calls” and the complex “songs” produced by males during the breeding season. Previous PAM studies observed pronounced Lombard responses for social calls, but findings for song remain conflicting. In Hawaiʻi, song chorusing dominates the soundscape during winter months, raising ambient levels by up to 20 dB. We identified song units and non-song calls in recordings from humpback whales instrumented with acoustic suction-cup tags off Maui. For all vocalizations, we determined received levels (approximating source levels), duration, frequency parameters, and the immediately preceding in-band noise level. Corroborating other studies, social call amplitude increased with ambient noise. However, the responses for song units were weak to nonexistent and depended on unit type, with some units showing a reverse effect of decreasing amplitude with increasing noise. Singers may already vocalize at the physiological maximum, limiting any Lombard response. These findings highlight possible implications for the communication space and encoded information of song, which is considered important within the humpback breeding system, in an ever-increasing noisy ocean.
Kügler et al. (Wed,) studied this question.