I'm looking after a garden for a friend at the moment.

There's a very large, very damp, and very uneven area of grass -- not
exactly lawn, but as near as they come to having a play lawn.

This patch is inhabited by a mole or few. When I was cutting the grass
in the season, the mole hills got regularly knocked down and amalgamated
(to some extent) by the action of the rode-on mower.

Now that we're in winter, I just noticed today that the molehills are
getting rather big.

Any advice on what to do with the molehills (and even the moles!). Do I
just leave them until Spring, and knock em down again with the mower, or
should I be taking action now?

Thanks a lot in anticipation,
John