This area has been observed regularly for at least 25 years, including the NJAS-sponsored Breeding Bird survey in the 1990s and a 2 times per week survey during 2003-2005. Daily records of all birds seen during 2003-2005 (available in Excel spreadsheet). Some recent issues of Records of NJ Birds for confirming evidence of some species, as noted below.
This area offers exceptional diversity and excellent habitat for migrants, breeding, and winter birds. Highest bird populations are seen during fall migration. Most of the data comes from access points along the Public Service RightOfWay in order to assess the total number of birds for the larger area we have extrapolated from the birds seen along the eastern and northern access points.
Entering Hatfield Swamp by canoe along the Passaic River, there are good populations of water birds not otherwise seen, including many Spotted Sandpipers, Kingfisher, Black-crowned, Green-backed and Great Blue Herons. Colony of 20+ Great Blue Heron nest at Troy Meadows and forages across Hatfield Swamp.
Raptors seen in the Swamp during the past fall migration include Kestrel and Merlin. Mississippi Kite was seen in spring '04 migration (Rec NJ Birds XXX, no3, p.73). About a dozen raptors species seen there in 2004. Owl populations are well known here, including wintering Long-eared Owl and Saw-whet Owl (Rec NJ Birds XXIX, no.2,p.35).
Many species concentrate here in high numbers during migration or over winter [ 5000 Am. Crow, see Rec NJ Birds XXX, no.2, p. 36] [ 700+ Blue Jay in one flock, personal observation, fall, 2004] [many sparrow species in large flocks in fall, Rec NJ Birds XXX, no. 3, p.76, and personal observations]
Several adjacent areas might be combined with Hatfield Swamp into one larger Important Bird Area territory since they also harbor superb bird populations in rather different habitats: Troy Meadows in Morris County, Great Piece Meadows and the Becker Tract in Essex County. Troy Meadows is a large wet marsh and includes many key water birds species: breeding Rails, Herons, Ducks, Marsh Wren, and perhaps breeding Raptors. Great Piece Meadows has more open meadows as well as much wet flood plain forest, but is less accessible.
Majority of this site consists of wet woodlands and small meadows lying in the flood plain. Several small streams and many drainage ditches run from the site into the Passaic River. During periodic flooding, water floods the woods, meadows and streams above capacity. Drainage ditches cause lower levels of water between storms so that most woods and meadows become partially dry. Most foliage has to be flood tolerant, since almost all portions do flood regularly. All portions lie within a few feet of the height of the main channel of the river; no high spots and almost no permanent ponds except for small vernal pools. Many invasive shrubs have moved into meadows and stream-side environments.