Nesting skylarks

I work for a golf club which owns a large field, not used for golf at all, but which is mown a couple of times a year to keep it tidy.  But it has been left so long that it has become a wildflower meadow and home to lots of nesting skylarks.  The boss wants it cut now as he says there is ragwort in it (there isn't).  My view is that it is vandalism of the worst kind to mow but does anyone know how the law would stand on this?