The Black Tern (Chlidonias niger) is a small tern species found across North America and Europe during the breeding season. It spends the rest of the year in coastal regions of Central and South America. The Black Tern has suffered significant population declines in recent decades and is now considered a threatened or endangered species in many parts of its range.
What is the Black Tern?
The Black Tern is a small, graceful waterbird in the tern family Laridae. It has a black head and body, gray wings and tail, and white underparts. The legs are red. In winter, the black feathers are edged with white, giving the bird a mottled appearance. Adult Black Terns are about 8-10 inches long with a wingspan of 20-24 inches.
Black Terns nest near freshwater lakes, marshes, and wetlands across Canada and the northern United States. They migrate long distances to wintering grounds along the Atlantic, Pacific, and Gulf Coasts, as well as parts of Central and South America. On migration and in winter, they are found in both freshwater and marine habitats like estuaries, bays, and harbors.
The Black Tern has a distinctive buoyant, buoyancy flight style, floating over water while dipping down frequently to catch fish and insects. Its diet is composed almost entirely of small fish and aquatic invertebrates. It feeds by plunge diving and dipping down to the water’s surface while in flight.
Black Tern breeding habitat
During the breeding season, Black Terns nest in colonies near freshwater lakes, marshes, ponds, and wetlands. They prefer shallow, vegetated wetlands with a mix open water for foraging. Nests are built on floating mats of vegetation, muskrat homes, logs, or clumps of rushes or reeds.
Both the male and female help build the nest, which consists of a shallow depression lined with plant material and debris. Nesting areas are often interspersed with the nests of other marsh-nesting waterbirds like grebes or coots. This provides some protection from predators.
The female Black Tern lays 2-3 eggs which hatch in 21-25 days. Both parents share incubation and feeding of the chicks, which fledge in 20-25 days. Parents will aggressively defend the nest and young, diving at intruders or performing distraction displays.
Some key breeding areas for Black Terns include:
– The prairie pothole region of the United States and Canada – shallow wetlands and marshes are important nesting habitat here.
– The Great Lakes region – wetlands along the lakes provide extensive breeding areas.
– Coastal marshes along Hudson Bay and James Bay in Canada.
– Wetlands across the boreal forest regions of Canada, Alaska, and the northern U.S.
Black Tern wintering habitat
During the non-breeding season, Black Terns are found along the Atlantic, Pacific, and Gulf Coasts of North America, parts of the Caribbean, and areas of Central and South America.
On the Atlantic Coast, they winter from as far north as Massachusetts down through Florida. Important wintering sites include coastal bays, tidal marshes, estuaries, and mangrove swamps.
Along the Pacific Coast, they are found from southern British Columbia down into Mexico. Key wintering regions include San Francisco Bay, coastal wetlands in Baja California, and mangrove estuaries along the Mexican coast.
In the Caribbean, they occur in small numbers in locations like Cuba, Jamaica, and Puerto Rico. Further south, they reach coastal areas of Central America and northern parts of South America like Venezuela.
Outside of the breeding season, Black Terns roost communally in groups ranging from a few dozen to over 1,000 birds. Roost sites provide protection from predators and weather and are typically located over water or on secluded beaches.
Black Tern population trends
The Black Tern has undergone substantial population declines across North America in recent decades:
- According to the North American Breeding Bird Survey, the Black Tern population declined by over 60% between 1970 and 2014.
- Christmas Bird Count data indicates a decline of 50% in wintering Black Terns from 1960 to 1988.
- Breeding populations in the Canadian prairies declined by 98% from the 1960s to early 2000s.
- Great Lakes breeding populations dropped by about 70% from the 1970s to 1990s.
As a result of these declines, the Black Tern is now classified as endangered, threatened, or a species of special concern in many U.S. states and Canadian provinces across its breeding range.
Estimated Global Population
1970s | 500,000-1,000,000 |
1990s | 100,000-500,000 |
2000s | 50,000-250,000 |
The global population was estimated at 500,000-1 million pairs in the 1970s but had declined to only 50,000-250,000 pairs by the 2000s.
Why is the Black Tern endangered?
The main reasons for the substantial declines in Black Tern populations are:
Habitat Loss on Breeding Grounds
Wetland drainage and degradation have severely reduced nesting habitat in key breeding regions:
- 50% of original wetland acreage in the prairie pothole region has been lost.
- Over 90% of coastal marshes along the Great Lakes were drained and converted to other uses.
- Hydrologic changes and development have impacted boreal forest wetlands.
This wetland habitat loss eliminates nesting sites and reduces food availability.
Habitat Loss on Wintering Grounds
Coastal habitat used by wintering Black Terns has also declined:
- Over 50% of mangrove forests have been lost in Mexico and Central America.
- Tidal marshes have been drained for agriculture and development.
- Wetland filling has occurred in coastal bays and estuaries.
This reduces food resources and available roosting habitat.
Disturbance and Predation
Black Terns are highly sensitive to disturbance. Human activities near nesting colonies can cause nest abandonment. Increased populations of predators like gulls, crows, racoons, and foxes may also contribute to nest failures and lower productivity.
Water Level Fluctuations
Nest flooding from unusual water level changes can wipe out entire breeding colonies. Climate change may amplify water level fluctuations.
Contaminants
Black terns are susceptible to bioaccumulation of contaminants like PCBs and DDT through their fish diet. This may impact reproduction.
Climate Change
Climate change will cause further loss of wetland habitat due to drought and sea level rise. Extremes in water levels and temperatures may also negatively affect nesting success and food availability.
Conservation efforts
A variety of conservation actions have been implemented to try to protect Black Terns and reverse population declines:
- Habitat protection and restoration – Protecting remaining wetlands and restoring degraded habitat increases available nesting sites and prey availability.
- Creation of artificial nest platforms – Floating nest platforms provide safe nesting sites and reduce flooding impacts.
- Control of disturbance – Restricting human access near colonies minimizes disturbance.
- Predator management – Using fences or wire exclosures helps exclude land predators.
- Monitoring and research – Banding studies and population surveys help track trends and inform management.
- Outreach and education – Increasing public awareness promotes conservation actions.
International cooperation is needed to protect habitat across the Black Tern’s broad migration routes. Continuing monitoring and habitat management will be necessary to stabilize populations.
Conclusion
The Black Tern faces an uncertain future after experiencing substantial population declines over the past several decades. Widespread habitat loss on both its breeding and wintering grounds, combined with threats like human disturbance, predation, climate change and contaminants have all contributed to its endangered status. Targeted conservation efforts like wetland restoration and protection, artificial nest platforms, and reduced human impacts near colonies may help recover Black Tern numbers. But a concerted, cooperative effort across international borders is required to reverse declines and ensure this graceful tern remains a wetland breeding species.