Dead starlings!

Over the last 2 months i have found 4 dead starlings in my back garden (near Chester), they don't appear to have been attacked - by all accounts look fairly healthy - though one could of possibly been a window strike but it just seems to be a strong coincidence to have so many in such a short space of time! 

I would like to pass info over to any local bodies that may take note of this in case it is not just isolated to my back garden, in case someone poisoning them or a possible illness effecting them. Hopefully it is just an unfortunate coincidence but I would rather be safe than sorry for the birds sake! If anyone could give any pointers or advice it would be appreciated.