The Sounds of Mother and Calf

While for humans, speech is our primary means of communication, for many mammals scent-marking is more important. This is not to say, however, that audible signals are irrelevant. This can be especially true for social mammals (such as ourselves), which often have a need for something more immediate and complex than the sort of long-lasting "keep away" or "I'm ready to mate" signals that scent marks can provide. Communication through sound can help keep a herd together, signal aggression, provide instant warnings, and so on. It's key to many primates, for instance, because most of them live up in the trees where it may be difficult to keep sight of all troop members when they are out foraging.

It's also important for many hoofed herd animals and, at least in the wild, few North American mammals are more sociable than the bison (Bison bison). While herds are no longer as vast as they were 200 years ago, recovery plans for the species are underway, and, in many cases, may rely on some degree of fencing or other containment at least for the time being. Understanding bison behaviour, including communication, could help with that, making it easier to assess how comfortable the animals are feeling - and, perhaps, the likelihood of a 750 kg (1,600 lb) bull deciding it's had quite enough of that fence and heading off somewhere it doesn't realise is less safe.

Learning to Hunt at Sea

One of the distinguishing features of mammals is that they invest a lot of time and effort in caring for their young. Of course, birds do this too, as do some other vertebrates, but the provision of milk is one of the key defining traits that's true of all living mammal species. (Probably most extinct ones, too, although it's hard to tell with the very early species). This means that newborn mammals are entirely dependent on their mothers in a way that the young of, say, most reptiles are not. 

But there comes a point where any mammal has to be weaned and make its way in the wider world. Even then, the maternal investment doesn't necessarily end with the mother continuing to raise and train her offspring for what can be an extended period. Brown bears, for example, are weaned at around six months, but they commonly stay with their mothers for at least another year, and often for two or more. We can see similar patterns in other mammals including, perhaps most obviously, primates.