Whale Watching Around The World Part 15
According to one theory, whales broadcast the song over a deep-ocean thermocline, a layer of water of a temperature particularly suited to transmit the low frequencies of whale sounds. The likelihood of the song being learned in summer and fall while mingling opens up additional avenues for exploring whale behavior. Some scientists now speculate that males sing to trigger the estrous cycle in females.
We may never learn the actual purpose of whale song. Mostly because humans lack the cranial capacity to comprehend the functions of a brain which is as far developed above ours as we are above a salamander. There is abundant evidence suggesting that male humpbacks use song as a warning to other males, in effect to stake out an acoustic spatial territory. On the other hand, song may be a competitive display, and only the best and most powerful singers will attract sexually receptive females. Scientists sometimes attempt to corroborate whale-song theory with information from elsewhere in the animal kingdom; the closest correlation may be the songs of birds. Songbirds also sing in identifiable, repetitive themes that vary according to the season and usually peak at breeding time.
Geographically distinct bird populations also have different dialects. A lot of what we know about birdsong, however, is not really in dispute. Ornithologists can identify a singing bird and observe its behavior practically all the time. Whale biologists are almost never certain which animal is the one producing a specific sound and can catch only fleeting glimpses of their subjects.
Whale researchers have made great strides in their ability to monitor the audible activity of whales. Biologists have tracked individual blue whales for more than 1,500 miles. The great range of the acoustical equipment permits researchers to gather data on the geographical distribution of whales during their migrations. And new auditory information is constantly revealed. The incredible moans of the blue whale are associated with reproductive behavior, and it seems likely that bowhead whales, like humpbacks, may produce a complex repertoire of song.
Even less understood than song are the social sounds of humpback whales. Furthermore, social sounds are not limited to humpbacks. Drop a hydrophone in the water in the vicinity of any active group of cetaceans to hear an astonishing variety of sounds. Some researchers describe hearing a trumpet or a train whistle when several humpbacks feed together. Other noises made by baleen whales can sound like monkeys, organs, groans, and knocks. Right whales produce sustained low moans among a number of other sounds, and bowheads generate enough distinct sounds to allow researchers based on arctic shore ice to track their migrations far out at sea.
Dolphins and porpoises, including orcas, produce higher-frequency whistles and clicks than baleen whales. Dolphins also clap their jaws in conflict situations. Biologists are fairly certain that bottlenose and spinner dolphins have signature whistles that broadcast the identity of the whistler. Bottlenose dolphins not only possess signature whistles, but also mimic the whistles of others, likely memorizing each other's whistles in much the same way as we repeat a phone number after snapping the directory shut according to some researchers.
Orcas go one step further and produce calls that may serve to identify an entire pod. The sounds produced by Antarctic orcas are different from those recorded off the west coast of North America. These mostly pulsed, repetitive calls are regular enough for scientists to recognize basic patterns. The sounds are common during travel and feeding, perhaps serving as signals to help coordinate activity.