Bird scarers

Hi,

I am, very passionate about my garden birds and have been thrilled to count at least 13 different species popping in to visit my feeders.  I was very excited to see a siskin for the first time this year, in fact I'd never heard of them before I started researching a new green bird but he is a regular visitor now.  I get a great deal of enjoyment from watching and hearing all of them. 

However my neighbours have decided that after many years they no longer want birds sitting on their fence or flying over it into any trees etc in my garden to perch, so they are trying to scare them off with silver foil ribbons and silver windmills which are positioned every couple of feet along their fence.

They have a very sterile, fully paved garden but were feeding the birds themselves last year and even talked about fitting a bird box which I hoped they wouldn't do because they have cats.  

They haven't said anything at all to me, the row of shiny and fluttery things just suddenly appeared about 40 cm above their fence a few days ago.   Thankfully the birds seem to ignore it all, and come in from different directions, although my numbers are down and the goldfinches have disappeared.  

I understand they may be fed up of the poop the messy starlings often deposit  but that's much easier to get rid of than the mess their cats leave in my garden.

I suspect this is more about upsetting me than the birds and I don't think what they are doing is illegal but is there any way I can curb this spiteful behaviour.