MadSci Network: Zoology


Date: Sun Oct 25 15:14:27 1998
Posted By: Andrea Bixler, staff (postdoctoral associate), biology, UM-St. Louis
Area of science: Zoology
ID: 908454335.Zo

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 

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 

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