Time for Nature

Life on the Islands

April 12, 2010

Terra Nova National Park of Canada

A migratory bird hotspot

With its abundant resources and wide variety of attractions, Terra Nova National Park of Canada is home to a highly diverse number of species. Among them are colonies of Arctic and common terns, who travel here to nest in colonies on islands off the park’s coast every summer. Both of these birds are long-distance migrators, but the arctic tern in particular is the champion in every respect. This bird has the longest migration of any animal in the world. In summer, the Arctic tern nests in Arctic and sub-Arctic regions and then flies south to over-winter near Antarctica, a journey of as much as 38,000 kilometres!

This island is home to a tern colony.
© Parks Canada 2008

An island is a fragile habitat

Since 1972, every year around mid-June, a team of park officers and volunteers travel by boat to these islands to count the number of nests and eggs. They do this to ensure the area’s ecological integrity is maintained. The birds avoid areas that are too rocky or too high and make their rudimentary nests with what little vegetation they can find. The eggs are well camouflaged but are sometimes taken by gulls, the eternal rivals of terns. Tides and the turbulent ocean also carry away eggs that are laid too close to the edge of the islands.

Tern eggs are well camouflaged.
© Parks Canada 2008

Don’t walk on eggshells here!

The teams make an initial sweep and the nests are counted and marked. Each nest represents a pair of birds in the data. Once the island has been completely explored, the team retraces its steps to make sure none have been forgotten. In recent years, the team has covered a total of 19 islands this way over the course of a week. Time is of the essence, because the incubation period is only 20 days, and any human disturbance drives the parents away, delaying the eggs’ hatching.

The team scours the rocky terrain for nests.
© Parks Canada 2008

Ecosystem bill of health

Terns reign atop their food chain, so their health is an indicator of the health of the entire ecosystem. However, research conducted by park managers indicate that the tern population in this area is undergoing a sudden decline. The number of nests has dropped by 10 percent since 2007 to about 300 nests, a worrisomely low level. The number of eggs laid has plummeted by 26 percent to only 591 eggs. For the time being, however, this number is considered viable and sufficient to maintain the colony.

Constant monitoring

The cause of this decline is not clear, and park managers are studying the matter. The Canadian Wildlife Federation is conducting its own aerial count of terns in Bonavista Bay, a large area that includes Terra Nova National Park of Canada. Park managers are cooperating with this organization to draw up an overall picture of the situation. Regional trends in recent years have seen a drop in the number of colonies, while the size of individual colonies is rising. The data confirm that this essential colony census work must continue with the same steadfastness shown by these migratory birds year after year.