WaterShrewCam

A new target for the trail camera and this one is tricky!  It started when I noticed a series of apparent false triggers on one of the otter cameras.  When I looked closely there was a tiny water shrew in the corner of the video.

Looking through the otter-less clips I found several with the tiny shrew swimming upstream at amazing speed as it returned from hunting forays in the pool below the culvert.  This is a montage of five episodes, the first two in a hailstorm.

Since then I have repositioned the camera a few times to get closer and better pictures.  This was the first attempt.

Then I removed the scrap of wood and the root to get a closer view.

Here is the shrew with prey, first a freshwater shrimp and then a caddis fly larva.  For the second one I have added a zoomed in view at 1/10 speed so we get a better view of the action.

Water shrews are mainly active at night, hunting underwater in complete darkness.  Like other shrews they have to eat very frequently so they are sometimes seen in daylight.  Paradoxically the camera found it more difficult to see the shrew in the day because of the high contrast between sunlit water and deep shadow under the bank.  Here is a little montage of daytime action.  This gives the best view of what I presume is soil excavated from a nest chamber in the bank, where the shrew disappears to at the end.

The water shrew (Neomys fodiens) is the largest of our three native shrews but is still small, slightly smaller than a wood mouse.  As you can see above it is an excellent swimmer and hunts for aquatic insect larvae, crustaceans and small fish under water.  It is very buoyant and pops to the surface as soon as it stops swimming.  It has a dense waterproof coat and hairy feet and toes which help it to swim.  Its nest is in a bank close to water with multiple entrances, some at or below the waterline and others higher to protect against flooding.  I found two small holes 30-50cm higher up the bank above where these videos were recorded.

You can read a fascinating paper investigating the sensory abilities of the closely related northern water shrew (Sorex palustris), including how it can smell underwater, here.

A few years ago I saw a water shrew in my garden on a trail camera.   Despite the video evidence I couldn't convince people what it was until I caught it in a Longworth trap and took photos to prove the ID - then they believed me!  Water shrews are occasionally found away from water, perhaps as they disperse from one site to another.

This one needs to be careful for there is another predatory aquatic mammal about, one 500 times heavier* and for whom the shrew would be just a mouthful.

* Tyrannosaurus rex weighed over 5,000 kg, so 500 times larger than an otter.  You can watch a brief David Attenborough video here, in which he talks about the water shrew and how it is probably similar to the earliest mammals that took advantage of the dinosaurs' extinction.