birds in captivety

Reading through the web site, reminded me of something i do not agree with. A neighbour of mine who is a control freak has two little birds kept in seperate small (very in my opinion)  cages and when weather permits hangs these 2 cages outside his window high up, and these little birds sing their hearts out, and it upsets me and others. Any help to find out what birds it's illegal to keep in captivety, and if not illegal for this breed the minium standards applied to size of cage for eg, would be most appreciated. Unfortunately i don't know the breed but am determined to find out as this is so wrong.Suggestions welcomed there must be lots of incidents like this, including protected species being kept captive, hawks spring to mind.    

All the animals have so much to teach us if we will only listen with an open mind