Birds of Linden’s Hawk Rise Sanctuary by
Kristin Mylecraine and Michael Allen, New Jersey Audubon
The Hawk Rise Sanctuary is a green oasis within the densely-populated Arthur Kill watershed in Linden, NJ. It has been open to the public since 2012, bringing scenic walking trails and great bird-watching opportunities to a natural area once gated off and hidden behind a variety of industrial land uses. The site contains a surprising diversity of habitats for its relatively small size and urban location. These include forested wetlands, vernal pools, grasslands, shrublands, salt marsh, mudflats, a large pond, and the tidal Rahway River. The equally surprising variety of birds and other wildlife these habitats support has made Hawk Rise one of the most popular birding destinations in the area. New Jersey Audubon (NJA) has partnered with the City of Linden for seven years, providing educational programming, stewardship guidance, and wildlife monitoring at the site.
Since 2010, NJ Audubon staff have been conducting year-round bird surveys in the approximately 40-acre Hawk Rise woods, as well as the adjacent Linden Landfill and Rahway River marshes, a total of almost 200 acres. The aims of these surveys are to assess the effects of habitat restoration and other stewardship activities; use this information to guide future management; and aid in designing educational programming at the site. Standardized surveys are conducted using a combination of point count and line transect surveys. Spring migration and breeding season bird surveys, when birds are singing and easier to detect, are conducted following standard point count methodology. Winter and fall migration surveys are conducted using line transect surveys, which are particularly useful when birds may be more spread out and less vocal. Following standardized and scientifically rigorous protocols allows for repeatability of surveys through time and detailed analyses.
A total of 163 bird species have been observed by NJ Audubon surveyors during the first five years of this project (2010-2014). This total includes five state-Endangered species (Bald Eagle, Black Skimmer, Least Tern, Northern Harrier, and Peregrine Falcon); six state-Threatened species (American Kestrel, Bobolink, Grasshopper Sparrow, Horned Lark, Osprey, and Savannah Sparrow), and 20 species of Special Concern (Blackburnian Warbler, Black-throated Blue Warbler, Black-throated Green Warbler, Brown Thrasher, Canada Warbler, Cooper’s Hawk, Eastern Meadowlark, Glossy Ibis, Great Blue Heron, Least Flycatcher, Nashville Warbler, Northern Parula, Semipalmated Sandpiper, Sharp-shinned Hawk, Snowy Egret, Spotted Sandpiper, Veery, Winter Wren, Wood Thrush, and Yellow-breasted Chat). Not too bad for a patch of habitat that many have probably driven by on the New Jersey Turnpike and written off as vacant land!
The opening of Hawk Rise Sanctuary boardwalk trails in 2013, the continuation of formal birding walks on-site, and the growing popularity of eBird checklists, has greatly increased the amount of observational data available. In just a few years, eBird users have submitted an impressive 214 checklists from the Hawk Rise eBird hotspot (https://ebird.org/ebird/nj/hotspot/L1867387) and recorded 24 species that were not recorded during our survey visits, bringing the 2010-2014 total to 187 species. This includes two additional state-Endangered species (Pied-billed Grebe and Red-shouldered Hawk), two state-Threatened species (Black-crowned Night-Heron and Red-headed Woodpecker), and five species of Special Concern (Black-billed Cuckoo, Blue-headed Vireo, Hooded Warbler and Least Bittern).
Habitats and bird use at the site
Hawk Rise forest: The forested portion of Hawk Rise Sanctuary, which contains abundant wetlands, is dominated by mixed hardwoods, including pin oak, sweet gum and red maple. In 2014 a deer exclosure fence was installed to promote understory vegetation regrowth.
Recent studies have shown the importance of riparian forests and habitats within urban landscapes as stopover habitat for Neotropical migrants. Our results suggest that Hawk Rise, a rare island of forest habitat within the densely-populated urban fringe of New York City, is used by a variety of songbirds during migration, and habitat management activities that increase the quality of migratory habitat could potentially benefit these birds. Surveyors have observed a greater diversity of bird species using the forested area during spring and fall migration than during the breeding season, including several species of Special Concern (Blackburnian Warbler, Black-throated Blue Warbler, Black-throated Green Warbler, Canada Warbler, Least Flycatcher, Nashville Warbler, Northern Parula, Veery, Winter Wren, Wood Thrush, and Yellow-breasted Chat). “Fall out” mornings can be particularly impressive on the eastern edge of the woods, with many of those colorful species plus others foraging together in the vine tangles catching the first rays of morning sun. The vernal pools in the western part of the woods are also consistently “birdy” during migration. It is not uncommon to hear the “chip” of a foraging Northern Waterthrush working the pool edge, or to flush up an American Woodcock resting up for its nocturnal flight.
In addition to neotropical migrants, the appearance of a Red-headed Woodpecker during fall 2013 created a buzz in the birding community, and suggests that this site has the potential to provide non-breeding habitat for this state-Threatened species. Throughout their range, Red-headed Woodpeckers were formerly common in urban areas with trees, but have been declined in these areas partly due to increased pruning of dead branches and removal of dead trees.
The forested area also provides breeding habitat for a variety of common resident and migrant songbird species, such as Black-capped Chickadee, Blue Jay, Baltimore Oriole, Great Crested Flycatcher, Gray Catbird, Tufted Titmouse, and White-breasted Nuthatch. Great Horned Owls frequent the site, and were confirmed nesting in 2012. Resident Wild Turkeys are commonly seen in the woods and on the landfill. Some of the more interior forest-nesting birds, such as Wood Thrush and Ovenbird have been largely absent from the site. Wood Thrush, a species of Special Concern, was observed during the breeding season in 2010 and 2011, but breeding status was not determined and this species was not recorded during subsequent breeding seasons. Ovenbirds are regularly encountered during migration, but have not been observed during the breeding season. Two interesting, but short-lived, mid-summer observations in the Hawk Rise forest were a singing male Acadian Flycatcher and a Yellow-billed Cuckoo. While these individuals likely did not stick around to breed, it is worth looking out for them in future years. Management activities to reduce the deer population, combined with habitat restoration efforts to increase native understory plants would benefit understory-nesting species at Hawk Rise.
Rahway River and Wetlands: The Rahway River and adjacent marsh habitat provide winter, migratory, and breeding habitat for a variety of waterfowl, passerines, shorebirds, and other waterbird species. The large pond between the Linden Landfill and a tank farm to the north also provides a unique habitat that has been consistently used by a variety of waterbirds during migration, though it is not currently accessible to birders. Flocks of Green-winged Teal, yellowlegs, and American Black Ducks are regularly encountered there, as well as the occasional rarity such as a foraging state-listed Black Skimmer in 2013 and Least Tern in 2014. A number of other state-listed species use the open water and marsh habitats of the adjacent Rahway River and tributaries for foraging. These include Osprey, Northern Harrier, Peregrine Falcon, and a variety of herons and egrets. Bald Eagles, too, have been encountered multiple times at the site, most often feeding along the river but once imposingly perched on top of the landfill! Migratory shorebirds, including Semipalmated Sandpiper, have been observed using the mudflats exposed during low tide during both spring and fall migration. Spotted Sandpiper, a state species of Special Concern, was observed at the site during all five breeding seasons of the survey suggesting likely nesting at the site. Although the survey protocol does not specifically target secretive marsh birds, Clapper Rail, Virginia Rail, and Least Bittern have all been encountered. A variety of songbirds nest in the marshes and shrubby perimeters, including Red-winged Blackbird, Marsh Wren, Common Yellowthroat, Willow Flycatcher, Song Sparrow, and Swamp Sparrow.
Linden Landfill: The grasslands currently covering the 50-acre Linden Landfill (closed since 2007) are used by a variety of common bird species, including Canada Goose, Killdeer, Wild Turkeys and Eastern Kingbird, but also provide migratory and breeding habitat for state-listed grassland breeding species. Grasshopper Sparrow, Savannah Sparrow, and Horned Lark were all observed using the landfill during breeding surveys over the course of the five-year survey. Grasshopper Sparrow and Savannah Sparrow are likely breeders at the site, as evidenced by repeated territorial behavior for both species and the presence of juvenile Savannah Sparrows during the breeding season. Singing male Dickcissels, a non-listed grassland bird, were also found on the landfill during 2012 breeding season and 2014 spring migration surveys. Eastern Meadowlark and Bobolink have also been observed during non-breeding periods, and a variety of raptors, including the state-listed American Kestrel, Peregrine Falcon, and Northern Harrier have been observed foraging over the landfill during migration and/or winter surveys.
The taller herbaceous and shrubby border along the road at the lower edge of the landfill provides habitat for a diversity of species during the breeding season, including Willow Flycatcher and Blue Grosbeak the latter of which is near the northern limit of its range. This edge habitat is particularly good for sparrows during fall migration where five years of surveys have documented (and a lucky birder might hope to see on a given morning): American Tree Sparrow, Field Sparrow, Savannah Sparrow, Song Sparrow, Swamp Sparrow, Lincoln’s Sparrow, White-crowned Sparrow, and White-throated Sparrow, Dark-eyed Junco, and Eastern Towhee. Migratory Palm and Yellow-rumped Warblers also frequent this habitat in fall.
NJ Audubon’s ongoing surveys at the site will allow us to assess the impacts of stewardship activities on bird populations at the site. As the City of Linden moves forward with deer management and habitat restoration at the site, it will be important to continue post-management surveys in a consistent and rigorous manner in order to detect any changes in bird use. Using repeatable, scientifically sound methodology for continued monitoring at the site will also allow us to determine whether restoration efforts are effective in improving forest health and providing habitat for wildlife at this site and will identify potential areas for additional restoration.
Visiting Hawk Rise Sanctuary
Visit this urban oasis during any season to experience its diversity of habitats and birds. The boardwalk trail system at Hawk Rise is open to the public, and is accessible from Range Road in Linden, New Jersey: http://www.njaudubon.org/SectionHawkRiseSanctuary/MapandDirections.aspx. The trail system winds through the Hawk Rise forest, continues along the edge of the Linden Landfill, and leads to an overlook of the Rahway River and adjacent marshes. More information about programs, volunteer opportunities, and other activities at Hawk Rise can be found here: http://www.njaudubon.org/SectionHawkRiseSanctuary/Introduction.aspx