Out of all of the shorebirds perhaps the most difficult to tell the difference between is the greater and lesser yellowlegs. According to The Sibley Guide the lesser is smaller with a shorter bill and it appears elongated and delicate. However these field markings are difficult to tell unless you have a greater and lesser near each other to compare.
At the shorebird workshop that I attended back in August, 7th - 10th, we were told that an easier way to distinguish the difference is that the greater appears to have a two toned bill compared to the single colored bill on the lesser. 
If you look at the first photo in the post you will see that the bill appears lighter at the base and gets darker as it gets nearer to the tip. Now compare that to the bird above who's bill appears to be a solid color. You may also notice that the bill on the greater, first pic, is slightly curved up compared to the very straight bill of the lesser.
It is also possible to confuse a yellowlegs with a solitary sandpiper. However solitary sandpiper have a much more defined white eye ring and there is much more noticeable contrast between the dark shoulder of the solitary and its lighter breast.
In flight yellowlegs are easily identified because there legs extend back behind the tail. This is true for both lesser and greater so to distinguish between the two type you need to look at the bill again. Since this bird has a straight solid black bill we would ID it as a lesser yellowlegs.
One bird that I forgot to mention, that is also easy to mistake for a yellow legs, is the stilt sandpiper. I mistakenly originally put in my stilt pics in place of my greater yellowlegs on this post. So I made the mistake even after taking the workshop. Fortunately one of my readers saw my error and sent me an e-mail, thanks Mike. I have now corrected the pics. 
If you look at the first photo in the post you will see that the bill appears lighter at the base and gets darker as it gets nearer to the tip. Now compare that to the bird above who's bill appears to be a solid color. You may also notice that the bill on the greater, first pic, is slightly curved up compared to the very straight bill of the lesser.
It is also possible to confuse a yellowlegs with a solitary sandpiper. However solitary sandpiper have a much more defined white eye ring and there is much more noticeable contrast between the dark shoulder of the solitary and its lighter breast.
In flight yellowlegs are easily identified because there legs extend back behind the tail. This is true for both lesser and greater so to distinguish between the two type you need to look at the bill again. Since this bird has a straight solid black bill we would ID it as a lesser yellowlegs.
The stilt sandpiper has more of a scale type of pattern on the back compared to the spotted pattern of the yellowlegs. It also has a shorter stockier bill.
4 comments:
Whew, still don't think I will be able to tell them apart. Maybe you will be around when I get a good enough photo to even start with. The ones I saw at the birding festival weren't close enough for me at all.
Beautiful images!
I also liked the ducks below and the little frog a little further down. All great animals and Watery shots.
I'm having a similar problem with Brewer's Blackbirds and the Common Grackle. I understand there is a size difference and that the bill is perhaps the easiest fieldmarker; but looking at dozens of photos of both...sometimes the BB's bill looks petite and sometimes it looks like a Grackle's. I cannot tell the difference and need to at least SEE a Brewer's Blackbird with someone who knows for sure...so I can be more certain!
Great Post...it's not easy, sometimes.
I didn't know what they were in the first place yet alone know there was a difference. :-) Thank for the info. The images are beautiful!
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