Working in collaboration with Richard E. Gies, lead volunteer of the Longwood Gardens Bluebird Project, Smithsonian Gardens established an Eastern Bluebird Habitat trail around the perimeter of the Greenhouse facility in Suitland MD. The nesting boxes were installed to benefit an existing population of Bluebirds as well as to encourage more bluebirds to nest on site. Eastern Bluebird populations are on the rise thanks, in part, to efforts like this one. The lack of suitable nesting cavities caused by changing land use patterns, increasing urbanization, and competition from introduced European starlings and house sparrows has been responsible for the decline of Eastern Bluebirds populations in the past. The roofs on these nesting boxes have been planted with a variety of stonecrop (sedum) plants. The purpose of the "green roof" is to help keep the interior of the boxes cool during the hot summer months. The green roof nesting boxes were designed Richard Gies for Longwood Gardens.