I have been reading about the diel patterns of vocalizing whales. Some baleen whales have been found to increase calling at night: blue whales (Stafford et al., 2005; Wiggins et al., 2005), North Pacific right whale (Munger et al. 2005), and humpback whales (Au et al 2000) to name a few.
Hypotheses which are related to mating, territory defense, foraging, sensing the environment, or a combination of these functions, among others. However, these whales still produce the calls during the daytime, just at lower rates.
Are there any marine animals that produce a unique vocalization only at nighttime (and not in the daytime)?