General Behaviour of Baleen Whales (Mysticeti): For the most part baleen whales are less social than toothed whales, which is not surprising as their prey (primarily small fish, krill and zooplankton) can not easily escape them and so there is little need for co-operative social hunting. There is a problem in discerning whether a group of whales is moving as a single pod or not. Whales like all cetaceans communicate mainly with sound and sound travels very well under water, in-fact in deep water certain low frequency whale sounds can be heard at distances exceeding 1500 miles (2400 km), even in shallow water whales can communicate over many hundreds of miles. This makes it difficult to know precisely if many whales all hundreds of miles away from each other are actually a single spread out pod or if they really are travelling alone. There is a lot of debate on this issue. Despite this it is generally held that baleen whales are not very social animals and do not have close family ties except between mother and calf, though this only lasts until the calf is old enough to leave the mothers care. For the most part baleen whales migrate to their polar feeding grounds where they stay for the winter and then migrate back down to more temperate waters to mate and give birth in the summer. It is the size of baleen whales that dictates their social trends, because they are so huge (for example a female blue whale can weigh up to150 tonnes) and their food is so small, there are few places rich enough to support large numbers of baleen whales for an extended period of time, hence large tightly knot pods would risk starvation. Also baleen whales are almost never attacked by other sea creatures, apart from occasional attacks from Orcas but those assaults are normally only directed against calves. All of these things mean that for baleen whales there is little advantage in forming large close knit groups, they do however sometimes travel in lose groups, though this seems to be more because they’re all travelling to the same place at the same time for the same reason, and not necessarily because they enjoy the company. Larger groups of baleen whales are sometimes seen where there is a particularly rich food source or in the mating season. Little is known about the mating practices of baleen whales and in the case of some species it has never been properly observed, for the most part mating is seasonal and takes place in the late spring or early summer, gestation periods vary but are all generally 12 months or more. The question of mating is often linked with whale song, the exact purpose of the songs is not know but it is assumed that they are used to attract females because the songs are only sung by males, normally when they are returning to the temperate mating grounds. However the songs are also sometimes heard in the arctic feeding grounds so some researchers believe that the songs are way of claiming territory and keeping a distance between rival males while others think it is a way of maintaining pod cohesion over vast distances. Humpback whales the whales most associated with singing (although the Beluga whale can actually produce a wider range of sounds) their songs can last from a few minuets in length to half an hour, once the whole length of the song has been sung the whale starts it again; they can be repeated for many hours or even days with pauses only for breath. The song sung by all the males is almost identical and changes a little each year until the song becomes completely different. Copies of their songs were on the golden plaque sent with the Voyager space probes.