American Oystercatcher Working Group

Habitat

Author: Jessica Stocking (JS), NC Cooperative Fish and Wildlife Research Unit , Dept. Biology, NC State University, Raleigh, NC.

Habitat: tied to coastal areas during breeding and non-breeding intervals, bound by prey specialization on shellfish and other marine invertebrates.

Breeding

Nests primarily on sand and shell beaches, dunes, salt marsh, and occasionally rock or other surfaces.  Typical nests are placed in areas with little to no vegetation, although substrate highly variable and dependent upon site type (Lauro and Burger 1989; Toland 1992; Wilke et al. 2005; Traut et al. 2006).

Historically, H. palliatus was considered to breed preferentially on outer beaches (Bent 1929).  Concurrent with the range expansion northward and apparent decline from Virginia to the south of the range (Davis et al. 2001; See Distribution), the oystercatcher has exhibited increased habitat plasticity.  This could be a function of survey focus.  A 2003 Virginia survey found 38% of pairs (n=588) in a lagoon system that had previously been omitted from systematic surveys.  The lagoon included marsh habitats such as shell rakes, wrack deposits, and sand ridges, often considered as non-traditional nesting habitat for H. palliatus (Wilke et al. 2005).  However, there is evidence that H. palliatus is actively changing habitats.  North Carolina barrier beach nesting decreased from 50% of total nesting in 2004 to 42% in 2010, as dredge island nesting increased from 16% to 30% over the same time period (NC Wildlife Resources Commission, unpublished).  This shift could provide relief from disappearing and increasingly less suitable outer beach habitat (Shields and Parnell 1990; Wilke et al. 2005) but may also cause birds to nest in sub-optimal habitat (Virzi 2010a).  The shift in habitat use could be a response to development, predation (Wilke et al. 2005) or human disturbance (McGowan and Simons 2006; Virzi 2010a), and is likely a combination of factors.

Barrier beaches: includes small residual dunes in periodically flooded areas and higher sandy areas that are part of a primary or secondary dune system, dominated by Ammophila, Spartina, Solidago sempervirens, or Laythurus japponica, well above mean high water.  Beach nesting on barrier islands takes many forms, including flat, open sand beach, interdunal areas, washover flats, and slopes of primary and lesser dunes.

Shell islands: low islands of accumulated shells, often created by wind or boat wakes (Sanders et al. 2008).  Shell islands appear to be an important nesting habitat for H. palliatus.  In one inlet in North Carolina, sixteen pairs nest on natural shell islands (Simons and Stocking 2011), and 20% of Virginia’s 2003 population was located on shell rake islands (Wilke et al. 2005).  In a survey of three springs in South Carolina, the majority of pairs were located on shell islands (Sanders et al. 2008).  Historical records from South Carolina suggest that pairs had nested on shell in 1921 (see Bent 1929) and 1944 (Sanders et al. 2008).  On the West Coast, and in Argentina, and on the Galapagos this species nests on shell banks: flat, narrow projections, 1–2 m above high water and made up almost entirely of unbroken shells; or on cobble spits (Bancroft 1927, EN).

Marshes:
low islands, surrounded by intertidal Spartina alterniflora marsh or mud flats, with a substrate of sand, tide wrack, and S. patens.  Early records of marsh nesting began to appear in the northern parts of the range (Frohling 1965, Lauro and Burger 1989).  Marsh nesting in the southern United States is also documented (Shields and Parnell 1990, McGowan et al. 2005b), but it is unclear to what degree due to increased monitoring effort in these locations.  Marsh nesting birds are usually more difficult to locate, as the vegetation in these locations provide cover for breeding adults and nests/chicks.

Dredge spoil: usually flat and nearly level elevated areas of various substrates—sand or gravel, sparsely to densely vegetated with Ammophila, S. sempervirens, and Artemesia stelleriana (Zaradusky 1985, Lauro and Burger 1989, Humphrey 1990).  American oystercatchers were recorded nesting on dredge spoil islands in 1986 (Parnell et al. 1986).  As outer beaches are becoming increasingly populated, dredge deposit sites may be providing alternate nesting sites, resembling barrier beaches in some respects while providing reduced mammalian predation pressure.  Also, the buildup of dredged material provides relief from the threat of flooding inherent in the lower marsh islands.

Rocky islands: In the West Indies, nests sometimes on small rocky keys (Edwards 1989, Raffaele 1989).  Rock nesting also documented on several islands in Boston Harbor (Paton et al. 2005).

Other: Nests have been located on gravel roofs in Florida (Douglass et al. 2001) and North Carolina (Cameron 2008, NC Wildlife Resources Commission, unpublished), an abandoned river barge in North Carolina (McNair 1988), and a capped landfill in Boston Harbor (Paton et al. 2005).

Migration And Winter

Typically concentrates in areas of abundant food, oyster beds, or reefs; clam flats and suitable roosting places; open ground without vegetation near suitable feeding habitat (Tomkins 1954, Cadman 1980, Jehl 1985).  Feeds in intertidal mud or sand flats, or on shellfish beds; roosts on adjacent beaches, dunes, or marsh islands, rarely venturing inland.

In a comprehensive survey of the wintering population along the Atlantic coast, found most often on shell rakes, but also often on sand spits and sandbars, and oyster reefs (Brown et al. 2005).  Dredge spoil islands were used in North Carolina (Parnell et al. 1986).  Commercially seeded oyster beds are a primary food source in Virginia (Tuckwell and Nol 1997b).  South Carolina hosts largest numbers (over 1/3 of total) of wintering H. palliatus along Atlantic coast (Brown et al. 2005).  Washed shell rakes were the primary wintering habitat (89% of total; Sanders et al. 2004).  Less used habitats were docks (6%), barrier island beaches (4%) and estuarine islands (1%).  Comprehensive surveys in coastal Virginia have categorized the habitats of known high-tide oystercatcher roosts with 35% on shell rakes and 24% on sandy beaches (TNC and VDGIF, unpublished).  In Argentina, wintering oystercatchers were equally abundant in estuarine and marine settings (Blanco et al. 2006).

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