ORIENTATION BY MEANS OF LONG RANGE ACOUSTIC SIGNALING IN BALEEN WHALES

With very few exceptions, whales are social animals. Even though they may be widely dispersed at some seasons, most species congregate in herds during some portion of the year. As a general rule, small, toothed whales form the largest herds, which frequently contain hundreds, and exceptionally tens of thousands, of animals, whereas the much larger baleen whales, when found in herds at all, most often travel in bands of less than 20 animals, with only occasional reports of herds of up to 1,000 animals or more.’ There has been considerable speculation on the functional significance of herd behavior in whales, but it seems unlikely that we will get any closer to understanding the role of herd behavior until we know more about what constitutes a herd. In general usage, the word “herd” seems to mean a group of animals that are in close enough proximity to offer visible evidence to an observer (usually on the deck of a boat) that their behavior is linked (i.e., they are swimming in the same direction, or breathing in rough synchrony, or feeding in the same area or resting together, and so on). But this is a visual judgment of what may be principally an acoustic phenomenon, and therefore is more than likely to be inappropriate. Since sound is conducted in the ocean so well and light so poorly, a functional social group of whales may be held together by sound rather than sight and may stretch far beyond the horizon visible from a boat, or even from an airplane, and what appears to be a lone individual may in fact be an animal traveling in company with one or many companions some miles away-by our definition, a whale in acoustic contact with another whale is not alone. This paper is concerned with baleen whales. Baleen whales are reticent laboratory subjects. In the absence of direct experimental evidence we might be able to get some idea of how far apart they can be and still be in acoustic contact by calculating how far their sounds might travel before being lost in the background noise of the ocean. Such calculations, while based in part on measured values, are also based on assumptions and remain theoretical. However, because of the exponential nature of acoustic phenomena, they are probably not entirely misleading. In this paper we will try to show what kind of useful range at least one sound made by one baleen whale species, the fin whale (Balaenoptera physalus) , might have and will suggest that its function includes long range signaling. We have chosen fin whales because they make exceptionally loud, low frequency sounds that have been the object of considerable study in recent years. It must be borne in mind throughout this paper that we are nor postulating meaningful communication of complex information among distant whales. Our remarks are concerned solely with simple signaling of place, for purposes of closing range and nothing more-in human terms, a message containing no more information than “there is a fin whale here.” Our thesis is that fin whales, and Rockefeller University and The New York Zoological Society, New York, N . Y .