Arctic Sonar Beams

Dolphins and porpoises are well-known for using biosonar to navigate their way around and detect the fish on which they feed. There are a large number of different dolphin species, with well over 30 in the Oceanic dolphin family alone, which includes not only the regular-sized species but also much larger "dolphins" such as the killer whale. Given this physical variety, and the variation in habitats between the different species, it's unsurprising that there are also many variations in the exact details of the sounds they emit and how they use them.

Much of this variation seems to date from the Middle to Late Miocene when both dolphins and porpoises underwent a rapid increase in the number of known species. This may be related to the loss of the connection between the Mediterranean and the Indian Ocean, creating a change in the worldwide circulation of water and corresponding changes in the habitats available to these animals, allowing them to exploit new opportunities.

Socially Awkward Mice

Many mammals have complex social lives, in which they have to interact with others of their kind in a multitude of different ways. Even those that predominantly live alone still require some degree of social interaction, especially during the breeding season, or when raising young. But for those that regularly encounter other members of their species, social interaction is particularly important, and its sophistication in primates was likely one of the key factors in the rise of humanity.

In the case of humans, of course, much of our social knowledge is built up as children, learning social rules through observation and experience as well as through more explicit instruction. And, while out ability to use language to impart detailed information is something that's essentially unique to us, the need for a suitable environment to fine tune social behaviour isn't something that just arose out of nowhere. Raising an animal in isolation from others of its species might not be as cruel as trying to do the same to a human child, but that's not to say that it wouldn't have some effect on them.

The Sound of Squirrels

It is, of course, well known that bats and cetaceans use ultrasound to help them navigate the world using sonar. However, there is no particular reason why animals should always make sounds that happen to be in the range of human hearing (and, arguably, some good reasons why they might not want to). So, taking the usual definition of ultrasound as anything higher than 20kHz - the approximate upper limit for the hearing of a young, physically fit human - it shouldn't be too surprising that other mammals use ultrasound for purposes like communication. Or, in the case of shrews, for actual echolocation.

There has been significant laboratory research on the use of ultrasound by mice and rats since at least the 1970s, but it has also become clear that they are far from the only rodents to make sounds beyond our hearing range. Last year, I talked about the potential use of ultrasound for sexual seduction among hamsters (and, to be honest, didn't reach much of a conclusion) and we also know that, for example, baby voles call to their mothers ultrasonically if they become separated.

In the case of squirrels, though, we know rather less, and much of what we do know applies to various kinds of ground squirrel. As recently as 2013, however, it was discovered that flying squirrels also use ultrasound, presumably for social communication. Indeed, the sounds were quite complex and varied, not mere repetitive squeaks, implying that they might impart rather more information that one might think at first glance.