Non-reflecting Pool

We were walking along The National Mall in DC being real tourists.

We were walking toward the Lincoln Memorial. We hadn't expected to do any birding that day. It was a gray & drizzly. When we reached The Reflecting Pool we were surprised to see it was mostly drained. It certainly didn't seem like habitat for shorebirds or waterfowl. Yet we found dozens of ducks dabbling in the pool as well as raising their families and amazingly, lots of peeps.

Semipalmated Plover.
When I listed the shorebirds we saw on eBird it turned out that plovers, Semipalmated Sandpipers, and the Dunlin we saw were rare birds for the area. When the pool is filled there isn't anyplace for them to go. On the other hand, what were they finding to eat on the cement? 
Constitution Gardens - Reflecting Pool 
Observation date:     5/18/10
Number of species:     15

Canada Goose     5

Mallard     100

Semipalmated Plover     2

Greater/Lesser Yellowlegs     1

Semipalmated Sandpiper     10

Least Sandpiper     10

Dunlin     1

Ring-billed Gull     5

Rock Pigeon     5

Mourning Dove     5

Blue Jay     1

Fish Crow     2

American Robin     5

European Starling     10

Common Grackle     10

House Sparrow     10