This video from Britain says about itself:
BTO Bird ID – godwits
17 August 2016
Godwits are large, elegant waders and relatively common in the right habitats at certain times of year. The two commonly encountered species, Black-tailed and Bar-tailed Godwit, should be reasonably straightforward to separate, although their eponymous tail markings may not always be the easiest feature to use! Some birds such as juveniles or out of context lone birds can prove more problematic, however, and this workshop will help you to confidently identify both species.