Seasonal and diurnal trends of chorusing humpback whales wintering in waters off western Maui

A portable data logger controlled by a Tattletale 7 microcontroller was use d to record humpback whale choruses during the 1998 humpback whale winter s eason in Hawaii. The data logger sampled the sounds for four minutes every half hour using a digitizing rate of 2 kHz, and the data were stored on a h ard disk. The results between January and April showed a peak in the sound pressure level between mid-February and mid-March. This peak of approximate ly 120 dB re 1 mu Pa coincided with the peak in the number of whales sighte d by aerial survey on 7 March 1998. The choruses had spectral peaks at 315 Hz and 630 Hz. Some of the sounds at 630 Hz were second harmonics of the 31 5 Hz peak and others were not: The data also indicated a diurnal pattern in the sound pressure level, with levels at night significantly louder than t he daytime levels. The sound levels began to increase during sunset and rem ained relatively high until sunrise, when they progressively decreased to a minimum. The nighttime peak occurred within an hour before and after midni ght, and the daytime minimum occurred between 1100 and 1500. That more hump back whales appear to sing at night may reflect a switch to sexual advertis ement as the primary male mating strategy at this time. It may also indicat e that daylight and vision play key roles in the formation of competitive g roups. It is suggested that the relative number of humpback whales in a giv en locale may be estimated by monitoring changes in sound pressure levels.