Athletes,
Olympian or just wannabes, spend time warming up and stretching before
competitions, but most mammals don’t bother with such niceties – they just get
on with it. Not usually for sport, but to eat and go about their life plan.
But
some mammals find their food of choice in cold water, so what is their species
strategy? They grow bigger and keep cool so they conserve energy to make few
but long underwater trips to feed. So when Campbell et al from U Manitoba got
down and dirty with their studies of the diminutive American Water Shrew, they
were in for a surprise (1).
Not
for S palustris the long dives, these creatures are only a
couple of inches long (not counting the tail) and they have to get in and out
quickly. Having to eat their body weight of small fish, dragonfly larvae,
tadpoles and other such delicious fare, that means a great deal of in and out,
with the cold water a constant challenge.
The
answer? They do their shivering first. This heats their body up, maybe by a
degree Celsius or more. Going in hot to trot, or rather dive, means that they
don’t slow down, get their target prey and are out again before their teeth start
chattering.
So
being contrary can sometimes work to keep small and beautiful. Being bigger and
slower isn’t always the best strategy, not that shivering on demand is an
easy trick to master.
