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.

Grey Seals on the Rebound

According to the IUCN Red List, which is probably the most widely used catalogue of conservation statuses, roughly a quarter of all mammal species are "threatened with extinction". That's a broader category than "endangered species", but, either way, it's a proportion that's growing. (As it is, of course for non-mammalian species; amphibians, for instance, seem to be doing particularly badly).

Partly that's because we're getting better at evaluating such things, and identifying species as being at risk when we previously knew little about them - or, in many cases, didn't even know they were separate species. But it's also a consequence of mankind's ever-expanding ecological footprint, as some species become threatened that weren't previously.

Pinnipeds: Grey and Harp Seals

Grey seal

There are four different species of seal that live off the coasts of northern continental Europe. Perhaps the best known is the harbour seal, or "common seal", which is also the most widespread of all seal species, being found across both the North Atlantic and the North Pacific. When the scientific naming of species was introduced in 1758, it was the only such species recognised from the area, but it only took a few decades for proper scientific descriptions of the others to follow, recognising that they were distinct from their "common" cousin.

The last of the four to be split off was the animal we now know as the grey seal (Halichoerus grypus), in 1791. While that's still fairly early as such things go, the fact that it was the last of the local seals to be formally identified as something different from the regular sort is likely down to the fact that it does look very similar to the harbour seal. Although, in fairness, it was first named by an entomologist, so clearly you don't have to be a mammal specialist to tell them apart.