This study makes use of previously collected aerial survey data, and uses a statistical technique called power analyses to assess whether current aerial survey methods allow changes in bird numbers to be detected, given that there are large background fluctuations in seabird numbers at any given site. Five species, two of which were combined due to the difficulty of separation were selected for analysis: red-throated diver (Gavia stellata), common scoter (Melanitta nigra), sandwich tern (Sterna sandvicensis) and lesser and greater black-backed gulls (Larus fuscus and L. marinus). Maclean, I.M.D., Skov, H., Rehfisch, M.M. and Piper, W. (2006) Use of aerial surveys to detect bird displacement by offshore windfarms. BTO Research Report No. 446 to COWRIE. BTO, Thetford.