Hart-Miller Island is an artificial island constructed from the severely eroded remnants of two islands in the Chesapeake Bay and millions of cubic yards of dredged material from the Bay?s shipping channels. The island is divided by a dike into two ?cells?. The north cell contains extensive mudflats, which attract some of the largest concentrations of migrating shorebirds in Maryland. The site is owned by the State of Maryland. The Maryland Environmental Service (MES) operates the dredged material placement facility for the Maryland Port Administration (MPA). The island is accessible only by boat and public access to most of the island is limited. Birders can visit the island on scheduled field trips organized by bird clubs affiliated to the Maryland Ornithological Society.
Daily numbers of shorebirds regularly exceed 1,000 in Spring and Fall, and can top 10,000 in years when water levels are ideal. The most numerous shorebird species are Semipalmated Sandpiper, Lesser Yellowlegs, Least Sandpiper, and Semipalmated Plover. The mudflats also act as a roost site for significant numbers of migrating Caspian Terns; 300-600 are regularly present during both Spring and Fall. In 2004, three species of high conservation priority in Maryland and DC bred here in small numbers. These were: the coastal plain subspecies of Swamp Sparrow, listed by the DNR as In Need of Conservation in Maryland, Spotted Sandpiper, a rare species in the state, and Willow Flycatcher, an Audubon WatchList species in the Yellow category.