Citation
Sparks, T.H., Huber, K., Bland, R.L., Crick, H.Q.P., Croxton, P.J., Flood, J., Loxton, R.G., Mason, C.F., Newnham, J.A. & Tryjanowski, P. 2007. How consistent are trends in arrival (and departure) dates of migrant birds in the UK?. Journal of Ornithology 148: 511. doi:10.1007/s10336-007-0193-6