Black and American oystercatchers are two similar looking shorebird species found along the Atlantic and Gulf coasts of North America. Both are large, strikingly colored black and white birds with long, bright red-orange bills used for prying open mollusks. While they occupy the same coastal habitats and fill the same ecological niches, there are several key differences between these oystercatcher species in terms of appearance, distribution, behavior, breeding and conservation status.
Appearance
Black and American oystercatchers look nearly identical at first glance. However, there are some subtle differences in plumage and morphology that allow keen birders to distinguish between the two species:
Size
American oystercatchers are noticeably larger with an average length of 17-18 inches compared to 15-16 inches for black oystercatchers. Wingspans are around 32 inches for American and 30 inches for black oystercatchers. As the name implies, American oystercatchers are the largest shorebirds found in North America.
Bill Color
The long bill used for probing and prying open shellfish is orange-red in both species. However, the bill color of American oystercatchers tends to be more vivid and intense compared to the duller, brownish-red bills of black oystercatchers.
Plumage
Both species are boldly patterned in black and white. American oystercatchers have more extensive pure white on the breast, belly and undertail coverts compared to the grayish-white underparts of black oystercatchers. The black plumage of American oystercatchers also has a brownish tinge while black oystercatchers are a pure inky black.
Legs
Black oystercatchers have yellow-orange legs. The legs of American oystercatchers are a fleshy pink color.
Eyes
American oystercatchers have bright yellow eyes compared to the brown eyes of black oystercatchers.
Attribute | Black Oystercatcher | American Oystercatcher |
---|---|---|
Size | 15-16 inches | 17-18 inches |
Wingspan | 30 inches | 32 inches |
Bill Color | Dull red-brown | Vivid orange-red |
Plumage | Grayish-white underparts, pure black above | Pure white underparts, black with brownish tinge above |
Legs | Yellow-orange | Fleshy pink |
Eyes | Brown | Yellow |
Distribution
Black and American oystercatchers have overlapping yet distinct breeding and wintering ranges along the Atlantic and Gulf Coasts:
Black Oystercatcher
– Breeding Range: Coastal areas from Massachusetts south to Florida. Also found along the Gulf Coast from Florida to Mexico.
– Wintering Range: South Florida, Mexico, Central America, and the Caribbean. Northern populations migrate south for the winter while some southern birds are year-round residents.
American Oystercatcher
– Breeding Range: Coastal areas from Nova Scotia south to Florida. Absent from the southern tip of Florida.
– Wintering Range: Coasts of the southeastern U.S from Virginia to Texas as well as adjacent Caribbean islands. Northern populations migrate south in winter while southern populations are year-round residents.
The breeding ranges overlap along the Atlantic Coast between Massachusetts and Florida. During winter, black oystercatchers shift entirely south of the range of American oystercatchers. The American oystercatcher has a more extensive overall breeding range while the black oystercatcher migrates further south in winter.
Habitat
Black and American oystercatchers occupy essentially identical coastal marine and estuarine habitats throughout the year:
– Sandy beaches and dunes
– Salt marshes and tidal flats
– Mangrove swamps
– Oyster reefs and beds
– Mudflats rich in shellfish
– Rocky coastlines
They forage along the intertidal zone probing for mollusks, crabs and other marine invertebrates. Nesting occurs right on the ground of sandy beaches, salt marsh islands, dredge spoils and shell mounds. The presence of suitable nesting sites free from mammalian and avian predators is a key habitat requirement.
While they utilize the same coastal habitats, black oystercatchers tend to occupy rockier shorelines more often than American oystercatchers. But in general, neither species is restricted to a specific coastal habitat type like salt marsh versus beach.
Behavior
Black and American oystercatchers share similar behaviors shaped by their marine coastal existence:
– Forage by probing or prying open shellfish along intertidal zone.
– Visually locate prey from a distance while walking along shoreline.
– Use their long bills to lever open or hammer through shells.
– Swallow mollusks whole or crush shells held tightly in bill.
– Nest on open beaches close to marine foraging sites.
– Form lifelong pair bonds and display high mate and nest site fidelity.
– Territorial during breeding season defending nesting and feeding grounds.
– Loud ringing calls used in courtship displays and territory defense.
– Distraction displays to lure predators away from nests and chicks.
– Chicks are precocial and able to feed themselves shortly after hatching.
However, there are some subtle behavioral differences:
– American oystercatchers are more gregarious in wintering flocks that can number in the hundreds of birds. Black oystercatchers form looser foraging flocks.
– American oystercatchers will nest in higher densities of up to 50 pairs per kilometer in prime habitat. Black oystercatchers nest more dispersed with 2-3 pairs per kilometer.
So in summary, black oystercatchers are more solitary and territorial while American oystercatchers are more social and congregate in higher densities. But overall, they share very similar coastal foraging and breeding behaviors.
Diet
The diets of black and American oystercatchers are nearly identical due to their specialized feeding on marine invertebrates of rocky and muddy intertidal shores:
– Oysters
– Mussels
– Clams
– Cockles
– Other saltwater mollusks
– Marine worms
– Crabs
– Urchins
– Barnacles
Their powerful bills allow them to pry open tightly closed shells or access mollusks cemented to rocks. They employ a variety of techniques to break through shells including hammering, wedging, cleaving and piercing. They will also feed on marine worms and crustaceans. Foraging is concentrated along the intertidal zone during low tides when prey is more exposed.
No notable differences exist in the main prey items consumed by each oystercatcher species. They are classic marine mollusk specialists feeding on largely the same shellfish, mussels and other invertebrates within their overlapping ranges.
Breeding
The breeding ecology of black and American oystercatchers is very similar in most respects:
– Nest on open coastal beaches, sand spits and islands Apr – Aug
– Nest consists of scrape or cup in sand lined with shell fragments
– Clutch size is typically 2-3 eggs (1-5 range)
– Both parents incubate eggs for 24-28 days
– Precocial chicks able to move about and feed right after hatching
– Chicks fledge at around 35 days old
– Most pairs raise 1 chick per year but up to 2-3 is possible
However, there are some subtle differences:
Courtship
– American oystercatchers engage in elaborate courtship rituals including synchronized calling displays.
– Black oystercatcher pairs perform minimal courtship displays before mating.
Parental Care
– American oystercatcher chicks are fed by parents for up to 6 weeks after fledging.
– Black oystercatcher chicks are independent sooner after fledging.
Double Brooding
– American oystercatchers will re-nest up to 2-3 times in a season if eggs or chicks are lost.
– Black oystercatchers rarely attempt to raise more than one brood per season.
So in summary, American oystercatchers invest more parental effort in courtship rituals, chick rearing and potentially raising multiple broods. But the core aspects of nesting, incubation and chick rearing are largely shared.
Vocalizations
The calls of black and American oystercatchers are distinct and make for a good field identification mark:
Black Oystercatcher
– Flight call is a high, piping “wee-wee-wee”
– Alarm call is a whistled “wheep”
– Advertising call is a whistled “wheep” given while flying in circles
American Oystercatcher
– Flight call is a loud, piercing “queep-queep”
– Alarm call is a whistled “queep”
– Advertising call is a loud, piping “quee-quee-quee” given in flight
So while the calls of each species are unique, they share a similarly high and piping quality often represented as “queeps” and “wheeps”. But the American oystercatcher has louder and more ringing vocalizations befitting its more social nature. Calls are one of the most reliable ways to identify these two similar-looking oystercatcher species in the field.
Conservation Status
Black and American oystercatchers have differing conservation needs and population trends:
Black Oystercatcher
– Listed as a species of Least Concern by the IUCN Red List.
– Global population estimated at 10,000-50,000 birds.
– Population appears stable with no significant long-term declines.
American Oystercatcher
– Listed as Near Threatened by the IUCN Red List.
– Global population estimated at 10,000-11,000 birds.
– Population declining at rate of 2% annually, a loss of 300 birds per year.
– Declines caused by habitat loss, disturbance of nesting birds and predation.
So the American oystercatcher is emerging as a species of higher conservation concern versus the still widespread and stable black oystercatcher. Protecting coastal nesting habitats will be key for the American oystercatcher’s long-term prospects.
Conclusion
In summary, black and American oystercatchers exhibit many similarities as large, vocal shorebirds that nest on beaches and rely on intertidal mollusks and marine invertebrates. However, American oystercatchers are distinctly larger in size, have more boldly patterned plumage and brighter bill colors, and exhibit more social behavior. American oystercatchers have a more expansive breeding range while black oystercatchers migrate further south in winter. The calls of each species are also diagnostic. Most critically, American oystercatcher numbers are declining while black oystercatchers remain common and widespread. Protecting coastal habitats is crucial for maintaining America’s oystercatcher populations into the future. Being able to distinguish between these two iconic shorebirds will become increasingly important for conservation.