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.
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.
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%.
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.
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.
- 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.
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.
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