Lame-Duck wrote in post #18930339
Jack, I've always had trouble telling the greater from the lesser yellowlegs. If they are both present, I go by size (the greater being a bigger bird). The bill on Robert's shot seems to show the bill kind of long, so I too think it might be a greater. The only other thing that I go by is the bars on the flank feathers, but this too is very often hard to discern.
What makes you think this bird is likely to be a great yellowlegs?
Well, I have trouble too, partly because we only ever see them over here as vagrants. We get a few Lesser Yellowlegs every year, but Greater is exceedingly rare. We have two closely related species - the Redshank and the Greenshank (some old books call the American birds Yellowshanks - I rather like that). Lesser Yellowlegs looks somewhat similar in build to our Redshank, but is more dainty, with a thinner, straight, almost needle-like bill (in comparison). Our Greenshank is a more sturdy bird than Redshank and its bill is slightly upturned. Greater Yellowlegs has just a hint of both these features. The bill on Robert's bird has just a hint of the upturn and, more importantly, is deeper at the base than I'd expect for Lesser Yellowlegs. So I go on build and shape first of all - but it's all very subtle and I am often unsure. On Robert's bird the streaking on the head and neck seems quite marked, which tends me towards Greater. On the other hand, the legs do look long, which might favour the more lanky Lesser, but that might just be due to the effort of lift-off.