sentences:  Revised editions appeared in 1955, 1962, 1968 and 1988.These editions were far more heavily revised than those of the original "Handbook", not least to take account of changes in bird taxonomy, as described in each edition's new forward.The 1968 edition complied with the then-new British Ornithologists' Union checklist, and incorporated further research by J. L. F. Parslow.