Identification of Solitary Sandpiper and
Lesser and Greater Yellowlegs
September 18, 2006
For the month of August 2006, the Great Meadows NWR in Concord , Massachusetts attracted remarkable numbers of Solitary Sandpipers (up to 50 in a day!), with smaller numbers of Lesser Yellowlegs and a few Greater Yellowlegs. This has provided an excellent opportunity to study the foraging behavior, postures and actions, of the three species and revealed a few differences that might be helpful for distinguishing them at times.
When actively moving and searching for food there seem to be consistent differences in posture and movements that could be useful at times to suggest an identification. I caution, of course, that this is based on only a few dozen birds at a single location, and the birds may act differently under different conditions. I’d be very interested to hear about how this works in other locations. Comments are welcome.
Foraging posture:
Solitary Sandpiper walks with head held up and slightly forward, higher then the level of the back, then tips quickly down to grab food items in the mud.
Lesser Yellowlegs usually walks with the head held fairly low and forward, the top of the head lower than the back, and tips forward quickly to grab food. Because it has longer legs than Solitary, the Lesser's body tilts more and tail comes up slightly higher when picking food from the ground. This species can walk with head held high, but (at least at Great Meadows in August 2006) actively foraging birds are pretty consistently in this posture.
Greater Yellowlegs usually walks with head high, upright and alert, and tips forward to lunge at prey, or runs with bill held in the water.
Foraging motions:
When Solitary Sandpiper tips down and touches its bill to the mud it nearly always gives several very quick forward and back vibrations of the head, as if trying to work the food up to it’s mouth, and simultaneously the tail, which is raised, vibrates up and down faintly.
Lesser Yellowlegs simply leans down, makes a single quick jab with its bill, and stands up again - no head-thrusting and no tail vibration.
Greater Yellowlegs is more graceful and controlled in all of it's motions, and usually leans down smoothly and more or less swipes its bill sideways through the water or mud.
We use size a great deal to identify birds, and one of the most important cues that we use to judge size is the relative motions of the birds. Hawkwatchers talk about how a kestrel is buffeted by light winds, but a Merlin (which is heavier) is less affected by turbulence and moves in a straight line even in windy conditions. These shorebirds are analogous. The smaller body mass of Solitary Sandpiper leads to a bird that moves more quickly, with more abrupt and "jittery" actions, and movement of the head and legs generates lots of body movement. In contrast the heavier Greater Yellowlegs moves relatively smoothly and slowly, and the heavy body remains fairly "solid" and stationary even as the head and legs move. Lesser Yellowlegs is intermediate.
