Large unusual birds being farmed/bred in pens

I'm trying to find out more about some large birds I saw recently in Cambridgeshire.

There must have been at least 15-20 birds kept in a large network of pens, giving the impression that they were being farmed or bred. Each was around 1.5m tall with white feathers apart from a black tail and neck. They had long pointed beaks, and made a very loud high pitched call which they would do in unison every so often. 

Apologies for the poor quality photo! I didn't take this myself but plucked it later from google maps. I'd be grateful for any ideas or suggestions.