Wildlife Response to Drilling for Gas

I live in a small hamlet called Llantrithyd in the Vale of Glamorgan, where Coastal Oil and Gas have been granted planning permission to test drill for gas.
The area is rich in wildlife and includes some rarer species such as the long-eared owl, green woodpecker and also some peregrine's.
At a recent village meeting, two ladies from Balcombe were invited to talk about their experiences. One of them lives half a mile from the drill site (much like me) and revels in the wildlife that is attracted to her garden. She, like many I would imagine, thought that the drilling would have no real impact on her life. However, from the moment the drilling started the birds left her garden and have not, so far returned. During her short speech she broke down momentarily, no act, just a woman in her 70's who, in her words, always voted conservative, read the Telegraph and thought that her way of life would be protected, where she was, by the powers that be.
So my question is: Why would the birds leave the surrounding area? Any ideas? Is it just the noise? (which we have been told is the same decibel level as a washing machine sat in the middle of a field)