Common merganser engages in cooperative fishing behaviour

Male common merganser.  A female hooded merganser is in the background.  Munson Pond.

I was at Munson Pond yesterday taking photos of birds.  The ice had just recently come off the surface and the entire water body was clear of it.  What was there in its stead were birds; hundreds of them.  The largest collection was Canada geese, but I was amazed at how many hooded mergansers there were too.  And then I saw them; large and colourful - male common mergansers.

In all, there were maybe a dozen common mergansers, both males and females.  The common variety were much larger than the hooded ones.  However, they didn't mind hanging out together, and they exhibited a most interesting behaviour.  They all dove at once.

Called cooperative fishing, it is a behaviour that increases the chances of any one individual catching a fish.  One bird on its own has to either be very lucky on its dive or has to chase down a fish fleeing for its life.  Many birds together change the odds, as a fish escaping from one predator may find its way into the jaws of another.

It was interesting to watch.  It always started out with a single bird, then a couple would join in, then the entire group would suddenly be underwater.  Wait for a few seconds, and they would all return.  Moments later, the scene would repeat.  Sometimes, one or two came up with a fish.  You can see the photo below of the group of mergansers on the surface; two are beginning their dive.

Common and hooded mergansers engaging in cooperative fishing.

Thanks for reading.

Eric Svendsen     www.ericspix.com