Am I missing something here, or don't neighbours communicate with one another any more? I'm certain that were it my next door neighbour, I'd be knocking on their door to point out the problem, politely, and to at least give them a chance to rectify it, rather than reaching automatically for the phone to have a whinge and moan about it to the RSPCA( IF you could ever hope to get an answer from them?), or to the Council's EHO.
Even if you're not on best terms with a neighbour, I guarantee that there is no better way of making it worse than by suddenly having the RSPCA or Council banging on their door to convey what you quite easily could do yourself.
No wonder you hear so much about communities not knowing one another nowadays. Long gone are the days of communication, now it's all a case of moaning and whingeing to the authorities, trying to get them to do our own dirty work, in this case under the pretext of concern for an animal, when in actual fact it's all about a reluctance to get off one's fat arriss to try to resolve it amicably. Give me strength!!!