Black Tern

(Chlidonias niger)

Status: Special Concern (ESA) and Not Listed (SARA)

Table of Contents:

Species Identification
Diet
Habitat and Range
Biology and Behaviour
Similar Species
Threats/Reasons for Being Endangered
Conservation and Recovery Strategies, Quick Facts
How You Can Help

Species Identification:

The Black Tern is a pigeon-sized bird with long tail feathers and a pointed black beak. Breeding plumage is mostly black with grey under feathers and sides, and spots of white on their wings and under the tail. After their post-breeding molt, adults have a mostly white head and grey body. Their short “kik” calls are used throughout the year and are often compared to the sound of a squeaky dog toy, while harsher calls are used during the breeding season.

Diet:

As with most terns, Black Terns eat mainly fish. Their diet varies according to availability, but they also feed on invertebrates like insects, crayfish, and small mollusks. They swoop down to pick food off plants or fish near the water’s surface.

Habitat and Range:

Ideal breeding habitats are shallow, freshwater marshes with lots of emergent vegetation. They nest in larger concentrations within the prairies of Canada and the eastern United States, but can also be found throughout the Great Lakes region. Their breeding range extends across the continent from British Columbia to Quebec in Canada, and across the northern states. They winter offshore along the western coast of Central America, and along the northern part of the South American continent.

Within Ontario, Black Tern populations are scattered throughout the Great Lakes, and in some northern parts of the province where there are suitable nesting sites. There are Black Tern observations recorded within the Land Between region.

Biology and Behaviour:

In early May, terns start arriving at their summer breeding grounds in Ontario. Site fidelity is variable, possibly corresponding to changes in vegetation structure. Most birds change mates each year, and courtship occurs during the next two weeks. The Black Tern is a semi-colonial nester, usually in groups of about 20 individuals in Ontario. They build a nest on whatever suitable substrate they can find, which is usually floating mats of vegetation. This could involve digging a depression in floating vegetation, or using old nests, muskrat lodges, or within broken down bulrushes. They lay 2-3 eggs on average, starting in late May. Since the nest is close to the water, it is prone to flooding. Both parents guard their nest area (approximately 2m diameter around), and will bravely guard their young by dive-bombing any threats. Eggs are incubated for about three weeks, and usually hatch by early July.

Parents feed their young for another two weeks, and the family group helps to defend the territory. Most foraging is within a few hundred meters, but they may travel a few kilometers from their nest site. Parents will protect their young by giving warning calls for them to race into the water and find shelter in tall grasses while the parents distract any threats. By August, terns gather in large flocks in bigger bodies of water. Most will begin their migration by mid-August or early September.

Predators have not been formally recorded, but are assumed to include large fish, herons, gulls, raptors, watersnakes, and snapping turtles. In Ontario the rate of nest success was found to be about 51%.

Similar Species:

The Black Tern is quite distinct in its breeding plumage since no other terns are black, but winter plumage may be confused with other terns. However, the Black Tern can always be distinguished by its black bill.

Threats/ Reasons for being at Risk:

1. Loss of wetland habitat: The majority of wetlands in southern Ontario have been lost due to development, and in central and northern Ontario, cottage development is leading to further wetland loss as people move northwards to escape the city.

2. Invasive species are deteriorating wetland habitat: European Common Reed Grass (Phragmites australis australis), European Frog-bit (Hydrocharis morsus-ranae), and Purple Loosestrife (Lythrum salicaria) are outcompeting native plants and changing wetland structure. The Mute Swan and Common Carp increase water turbidity and impact submerged vegetation.

3. Population growth and residential expansion: Ontario’s population continues to grow, thereby putting pressures on wetland and lake habitat due to residential development and recreational use. Boats and jet skis can also damage and flood black tern nests if they come too close at high speeds.

4. Pollution: Mirex (a banned flame retardant and insecticide) occurs in Lake Ontario, and has been found in Black Tern eggs and tissue. Pesticide use can also lead to egg-shell thinning, and affects the abundance of their prey (e.g. insects and other invertebrates). Many pollutants are found in wetlands across Ontario and are impacting a great deal of important species.

5. Climate change: Climate change is an overarching threat where resulting changes are expected to exacerbate the loss of wetland habitat and produce conditions that favour invasive species, especially those listed above. As natural wetland habitat decreases, so will Black Tern populations.

Conservation and recovery strategies:

The province’s management strategy involves identifying and monitoring the range and threats for this species. There are plans to recover habitat by working with landowners, different levels of government, and interested organizations.

There have been initiatives to conserve wetland complexes through conservation easements.

Under provincial legislation, new roads, aggregate pits, or activities that draw down water are not permitted in suitable wetlands that have had a Black Tern within the past 10 years, and a 20 hectare area around the site must also be protected.

Quick Facts:

The Black Tern and the Forster’s Tern are the only marsh-nesting terns that breed in Ontario.
A separate population of Black Terns live in Eurasia. Numbers of these birds have also seen severe declines in the last few decades due to similar issues.
The presence of muskrats has been shown to be beneficial for Black Tern breeding sites. Muskrats may feed on invasive plants and allow for the desired ratio of water to vegetation. They also help to ensure that more nest substrate is available for Black Terns.

How can you help?

Be a respectful boater! Drive your boat slowly around wetlands and shorelines to reduce the damage from wakes. Never drive a Jet ski into shallow waters during breeding season.
Artificial nest platforms can be installed in suitable wetlands. These have been successful in northern states, especially when dead vegetation is placed on top. They should be moved annually to dissuade predation.
Protect existing wetlands. On your property maintain wide riparian buffers and keep lights and pets away from the wetland. Talk to your local government officials and conservation organizations to help wetlands in your broader community.
Participate in local efforts to control invasive species.

Additional Resources:

Nature Canada’s species spotlight.
Cornell Lab of Ornithology page.
Audobon Society’s profile.
The Black Tern is included in the MNRF’s guidelines for forest practices.

Sources:

Peter S. Burke. 2012. Management Plan for the Black Tern (Chlidonias niger) in Ontario. Ontario Management Plan Series. Prepared for the Ontario Ministry of Natural Resources (OMNR), Peterborough, Ontario. vi + 47 pp.