|MadSci Network: Zoology|
I thought this was going to be an easy question to answer. I figured I could just say, "no, they can't ALL swim," and name several groups of mammals that can't swim, and be done with it. It turns out that a lot more mammals swim than I would have thought, and therefore I am beginning to wonder if maybe they all can swim. I'm sure you are familiar with the aquatic mammals (whales, dolphins, seals, sea lions, walruses, otters) whose (almost) exclusive mode of locomotion is swimming. You may also know of the mink, capybaras and nutria (coypus) that are semi-aquatic. You may not know of the following swimming mammals: the common long-nosed armadillo of South America; the desmans, which are in the same family as moles, but live in the rivers and streams of the Pyrenean mountains and Russia; the fish-eating rats and mice of South America; the European water shrew; several species in the tenrec family (relatives of shrews that live in Madagascar and Africa), including the giant otter shrew, the Mount Nimba least otter shrew and the aquatic tenrec; water voles, which live in western Europe; and the water opossum and little water opossum of South America. There are probably many others, but this sample gives you at least some idea of the taxonomic diversity of swimming mammals. Many of the species I've mentioned have obvious adaptations for swimming. The armadillo can inflate its stomach and intestine with air to improve buoyancy. The desmans and fish-eating rats and mice have webbed toes, at least on their back feet, which provide much of the propulsion in the water. Desmans can close their ears and nostrils to keep water out, and water opossum females can close their pouches tightly enough to keep dry any babies that might be inside. So at first glance, it might seem that any mammal with appropriate adaptations (such as webbed feet) can swim. However, water voles apparently have no specific adaptations for swimming, yet they do it very well. And many other mammals without specific adaptations for swimming, such as antelope, cats, bears, dogs, elephants and even skunks, swim quite well, either by choice or when they have to. There are, however, mammals that cannot swim. Apparently the above-mentioned common long-nosed armadillo is the only armadillo species that can swim. I seriously doubt that many arboreal species such as sloths ever swim, so the only way to find out if they _can_ swim would be to throw them in a pool of water and not let them climb out. This is not the type of experiment many scientists are inclined toward nowadays. And bats, which you specifically mentioned, do not swim, as far as I know. I feel obliged to say "as far as I know," because there are so many species of bats (800?) that it would be easy to miss some that do swim. Many bats forage over water, diving to the water's surface to drink or grasp fish, frogs or insects, but I do not think they actually go under the water and swim. I think this brings me back to my original answer--not all mammals can swim. But certainly many more of them can, and do, than I would have ever suspected before researching this subject. Thanks for making me learn something!!
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