The Silver Fern looks nice to us Kiwis because we know what it is. But most foreigners see a white feather which is pretty much what it looks like. Not very symbolic.
A stylised Kiwi might work even if nobody else knows what it is.
Think about other countries flags: there are very few which are immediately recognisable. Stars and stripes, maple leaf, hammer and sickle, red sun...dunno about others.
We are living in a global age where the significance of flags is diminished so all in all, I don't think a change is worth while.
Bookmarks