by: Ross Hall
FALL 1995
Along the Nova Scotia and New Brunswick border, there are several large man-made freshwater marshes. These marshes, which were once used for hay and as dykes, were purchased by the Canadian Wildlife Service and the Nova Scotia Department of Lands and Forestry. Developed with the help of Duck Unlimited, water control structures and dykes were constructed to stabilize and control water levels.
The Missaguash Marsh was the first wetland developed, followed by the Tintamarre Complex in New Brunswick and the Amherst Point Sanctuary and East Amherst Marshes in Nova Scotia. Underlaid with marine silt, these marshes are extremely productive.
Developed initially for waterfowl, many unusual and migratory non-game marsh birds live on these marshes. One bird species attracted to these marshes is the black tern (Chlidonias niger), which mainly nests on inland freshwater marshes. Other tern species seen in Nova Scotia are white in colour and are seen along the coastline.
Black terns are smaller than common and Arctic terns. When breeding, their plumage, bill, head, and back are black. The wings and tail are various shades of grey. They seldom dive, preferring to pluck their food from the surface.
Black terns build their nests upon floating piles of dead vegetation, such as cattails or bur-reeds, floating mats of muck, or similar materials. The nest consists of a small gathering of aquatic vegetation in a cup-like bowl. Eggs are often only a few centimetres above the water level. Because of the nest location, wind, heavy rains, waves, or flooding can damage the nest or harm the eggs. this risky location choice is preferred to the marsh edge, where many mammals that rob nests roam.
Nesting materials often change from one year to the next, which explains why black terns move to different marshes in different years. In 1993, black terns nested on the East Amherst Marsh, but they are nesting on the Amherst Point Marsh this year. This border colony of black terns has changed nesting locations many times since they first nested at Tintamarre in 1967.
Black terns have two interesting courtship flights. In "high flight", 2 to 20 terns ascend together to a great height then split into small groups of two or three and descend in rapid glide. During the "fish flight," a male tern carries a small fish or large insect in its bill and is closely followed by a female as the two fly about the marsh. At the end of their aerial display, the male follows the female to a perch and feeds her.
Both adults incubate the one to five eggs that are laid, which hatch in 20 to 23 days. The chicks can swim, walk, and run by the time they are two days old. If disturbed, thy can hide in vegetation. they can fly by 21 days. Terns often lay more eggs if the first ones are lost.
On the breeding grounds, black terns are primarily insectivorous, eating damselflies, dragonflies, and mayflies. They also eat small crustaceans, spiders, and small fish.
Nova Scotia black terns migrate to the coast, then south to wintering grounds from Panama to Peru and Surinam. In winter, they have white underparts and a grey back.
Although black terns now nest in Nova Scotia, it is still a fragile occurrence. Despite a near continent-wide distribution of black terns in North America and the occurrence of a subspecies in Europe, the U.S. Fish and Wildlife Service Breeding Bird Survey indicates a population decline for at least the past 20 years. From 1966 to 1989, the breeding population in North America declined at a rate of 5.6 percent per year, for an overall decline of 71.8 percent. In the United States, many states within its breeding range list black terns as a species of special concern or an endangered species. In Canada, it is proposed as a threatened listing.
The loss of habitat contributes to the decline. Since European settlement, it is estimated 52 percent of all wetlands in the United States have been lost. In Canada, losses are similar. Seventy percent of southern Ontario's original wetlands have been converted to other uses, particularly agriculture. Along the St. Lawrence River, 42 percent of wetlands from Cornwall, Ontario, and Matane, Quebec, were lost between 1945 and 1975.
At Montezuma N.W.R. in New York State, one thousand pairs of black terns nested in the late 1950s, but less than 10 pairs are now present. Purple loosestrife (Lythrym salicaria), an invasive wetland exotic that out competes native plants, has drastically altered wetlands such as Montezuma.
Several studies have detected pesticides in black tern eggs and organochlorines are linked to low reproductive success. It is suspected that many of the contaminants may be accumulated while terns are migrating on their wintering ground.
Weather, predation, diseases, and parasites affect black tern populations, but are not new threats. Human disturbance is a factor. As with all tern species, incubating or brooding black terns will leave the nest at the approach of people. Repeated or prolonged disturbance may increase the likelihood of abandonment, predation, or exposure to inclement weather. for black terns, small boats such as canoes are a great threat. People viewing black terns or travelling near a nesting colony should keep at a distance so the birds are not disturbed.
Terns are birds of great energy and mystery. They make great journeys to southern continents. We must hope they will return each year to raise young on our border marshes, and we must do what we can in this small section of the world to protect them.