Common terns are small colonial nesting seabirds that some might say are the most graceful here in our freshwater paradise of northeastern North America. Although their population is only a fraction of what it used to be in the Great Lakes, recent management actions in the U.S. and Canada have helped to maintain several healthy colonies. Historically, terns in the Great Lakes nested on small rocky islands or shoals, but in recent decades they have come to be more and more dependent on the 8m diameter Seaway Navigation Cells (channel markers).
This spring, before beginning my research on contaminants in terns, I had the opportunity to help out Lee Harper, the lead biologist for the Upper St. Lawrence River tern management initiative. Most of his work is behind the scenes (i.e. before the terns arrive each year in late April), spending several days out on the water improving habitat at most of their known nesting sites. Habitat improvement projects require knowing in advance what habitat features terns prefer. And like any good management plan, decades of scientific observation and experimentation have realized several key features of good tern habitat.
Because terns are relatively small seabirds for the Great Lakes, they require a good degree of isolation and protection from would-be predators like gulls and herons. In addition to the isolation of nesting on rocky shoals and navigation cells, they tend to favor sites with fine substrate such as pea-gravel to form their nests on the ground. But first, because the gulls return to the breeding grounds about a month before the terns, we set up mono-filament exclusion grids that prevent the wider wingspan of a gull from landing on would-be tern habitat. We also put out several “chick shelters” that offer protection from potential predators and a shady place for young chicks to rest during the hot summer days. Lastly, we put up 30cm tall mesh fencing around the edges of the colonies so that chicks don’t jump into the water and get washed downstream before they are old enough to fly back.
Once all these things are in place for the breeding season, we get to wait for a few weeks as the terns slowly arrive on the breeding grounds and begin to find their mates and choose a suitable territory within the small colonies. Then the real fun begins of monitoring reproductive success and banding chicks...I’ll talk more about this in a later post when I discuss my research in more depth.
