Barn Owls are afforded the highest degree of legal protection under Schedule 1 of the Wildlife and Countryside Act 1981. This means that if anyone “intentionally or recklessly” disturbs a Barn Owl (or any other bird listed in Schedule 1) whilst it is “in, on, at or near” the nest or whilst it has dependent young, and without the necessary Licence from Natural England (or other licensing authority), they may be committing a criminal offence punishable by a fine of up to £5,000 and/or a prison sentence of up to 6 months.
So, if your Owl (and its partner) were nesting on the land in question it would be illegal for the developer to disturb the birds during the nesting period. Unfortunately, however, once nesting is over and the young have dispersed there is nothing to stop the developers from destroying the nest site/territory. Similarly, a Barn Owls hunting ground is not, in itself, statutorily protected.
Having said that, it may be worth alerting your local council's ecology officer to the situation as, depending on the land area in question, he/she may be able to persuade the developers to incorporate some compensatory habitat in the development and, if the land surrounding the development site is suitable, to perhaps even install some Barn Owl boxes on the periphery - just a thought.
Hope that helps
Jeff
(Schedule 1 Licence holder for Kingfishers, Barn Owls and Avocets)