Black-Tailed v Bar-Tailed
Black-Tailed Godwits are wonderful birds. Here are some in flight over the River Exe.

Black-Tailed Godwits are often confused with Bar-Tailed Godwits – by me if nobody else.
Black-Tailed Godwits (or Blackwits as those in command of the secret birding knowledge call them) have longer legs, which stick out in an ungainly fashion behind their tail. They have a straighter bill, and a marked preference for freshwater. Does that help? There are no prizes for guessing that Bar-Tailed Godwits (yes, Barwits) have shorter legs, an upturned bill, a preference for the coast, and streaky tails.
Here’s a Black-Tailed.

Here’s a Bar-Tailed Godwit in flight:
Actually, I have a much better photograph of a Bar-Tailed Godwit in flight. You can hardly see the toes on its shorter legs, hidden under its tail:
As you can see below, there’s also the small matter of Black-Tailed Godwits having a very distinctive white v-shaped pattern on the outstretched wings.
Whichever species you see, they are wonderful.