Bibby, Colin J. (2003). "Fifty years of Bird Study: Capsule Field ornithology is alive and well, and in the future can contribute much more in Britain and elsewhere". Bird Study. 50 (3): 194–210. doi:10.1080/00063650309461314. S2CID87377120.
Bibby, Colin J. (2003). "Fifty years of Bird Study: Capsule Field ornithology is alive and well, and in the future can contribute much more in Britain and elsewhere". Bird Study. 50 (3): 194–210. doi:10.1080/00063650309461314. S2CID87377120.