Fort Harrison State Park, a 1700-acre Important Bird Area located in northeastern Marion County, offers perhaps some of the best breeding habitat in the greater Indianapolis region for neotropical migrant and forest-dependent birds. WatchList birds such as Cerulean Warbler, Prothonotary Warbler, and Kentucky Warbler can all be found commonly here during the summer months.
Formerly a military preserve purchased by the federal government in 1904, the property was acquired by the state in 1996 following a major a decommissioning by the Armed Forces, and Fort Harrison State Park now stands to preserve most of the greenspace and natural areas that the Army kept out of development for most of the 20th century.
Given its location within the urban sprawl of the greater Indianapolis area, Fort Harrison State Park contains significant parcels of floodplain and upland forest tracts; these habitats are a vanishing natural resource in Marion County and indeed in central Indiana as well. Consequently, this Important Bird Area supports one of the richest and most abundant breeding bird communities within this region of Indiana. In fact, summer counts and surveys for breeding birds often exceed 80 species at this locale.
The riparian and floodplain forest which line Fall Creek on the northern portion of the state park play a critical role in the site's ornithological significance. At least three species of WatchList birds are relatively common along this wooded tract - Wood Thrush, Cerulean Warbler, and Prothonotary Warbler. The populations at Fort Harrison of these three species probably represent the greatest abundance for each in Marion County. Other neotropical migrants can be found in this area during the summer months; species such as Acadian Flycatcher, Northern Parula, Yellow-throated Warbler, and Louisiana Waterthrush breed in these wet woods. Additionally, the riparian habitat supports what is likely one of the largest breeding population of Brown Creeper in the state, which is a rare nester in Indiana, as well as a significant Great Blue Heron rookery, typically numbering over 100 active nests each year.
The upland forest and ravines along Lawrence Creek located in the western part of Fort Harrison also support an important diversity of breeding neotropical birds. Several pairs of Kentucky Warblers, a WatchList species, nest here, as does the Hooded Warbler, which is listed as a species of special concern on the state conservation registry. Notable, too, is the presence of nesting Ovenbirds in this section of the IBA; this species, which prefers dense, mature stands of forest, has virtually disappeared as a breeding species from other locales in central Indiana.
As with most isolated habitat patches within highly developed urban landscapes, the floodplain and upland forests found at Fort Harrison State Park are the last vestiges of more extensive habitats that once existed along the Fall Creek watershed in central Indiana and must accordingly be managed and protected judiciously to ensure a future for the species of birds that are otherwise scarce in Marion County and its surrounding environs.
Many conservation threats associated with urban landscapes are found here, most notably the increasing population of non-native invasive shrubs such as bush honeysuckle and autumn olive. Such vegetation threatens overall floral diversity and impacts the productivity of birds breeding within these shrubs. Additionally, as the stands of upland and riparian trees continue to mature, the pervasive non-native vegetation will inhibit the growth of the next generation of overstory hardwoods, thereby threatening the future availability of habitat for many of the site's nesting forest-dependent birds.
Similarly, considering Fort Harrison's placement within the urban landscape, nest predation and brood parasitism are most likely insidious problems at this site. Brown-headed Cowbirds are common residents during the summer months, and the state park has noticeable populations of nest predators such as squirrels, raccoons, and feral cats. Unfortunately, because of these threats to breeding success, it is likely that the area is a ecological sink for many species' populations.
However, active habitat management at Fort Harrison could help increase the site's overall species richness. Although limited in patch size, several opportunities exists to help create better grassland and shrubland habitat within the park, especially in areas of existing power-line utility easements, the former location of the military land fill, and the surrounding environs of the park's two major open wetlands - Delaware Lake and Duck Pond.