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September 2, 2007

On the Wing: Habitats face varied threats

By Kay Charter

While it may not seem plausible, the use of cypress mulch in gardens, a cormorant population explosion in the Great Lakes and "beach grooming" have a great deal in common. All three, in fact, result in significant habitat destruction.

In late spring, Grand Traverse Baykeeper John Nelson wrote a letter to the editor about the importance of cypress wetlands along the Gulf Coast. Nelson pointed out that these watery woodlands stabilize our coastlines against storm surges and erosion and are therefore the first line of defense against hurricanes. He added that they also serve as critical habitat for migrating birds.

Roughly 60 percent of all U.S. bird species pass through these rich, wet forests during migration, making them one of the most critical links between temperate breeding grounds and tropical wintering areas. It is known that birds returning from South and Central America depend on healthy coastal habitats after grueling trans-Gulf flights.

From an ecological perspective, spreading cypress mulch on your garden can be compared to burning an irreplaceable piece of art to warm a room. Neither makes much sense.

Double-crested cormorants have experienced population swings in Michigan during the last century. Named for the rarely seen crests on its crown, this is one native species many fishermen and women love to hate because the bird is blamed for adversely impacting sports fish. While some believe the evidence for that is contradictory, there is no question that today's rapidly growing cormorant population in our area is causing habitat destruction.

While nesting cormorants were considered a rarity early in the 20th century, they became so common in Ontario by mid-century that control measures were instituted.

By the late '50s, however, widespread use of DDT decimated many avian populations, the rapidly expanding cormorant population among them. By 1966, the breeding population for the entire Great Lakes was a mere 30 pairs, far below their long-term average. With the elimination of DDT, the avian reproductive success again rebounded and by the 1980s the double-crested cormorant population was increasing by nearly 40 percent a year.

Cormorants are colonial nesters, which means that they nest close together in large groups. One of the places they have colonized is Gull Island off Northport in Grand Traverse Bay. Gull Island has historically served as a rookery for herring and ring-billed gulls and the state-threatened Caspian tern.

Nesting cormorant numbers on Gull Island grew exponentially over the following two decades, ultimately causing a decline in the numbers of all gull species, including the terns. not only were nesting gulls and terns displaced, but abundant bird droppings across the island eventually killed vegetation that had been used by nesting songbirds such as song sparrows and yellow warblers. This was clearly habitat destruction by too much of a good thing -- in this case, unnaturally high numbers of nesting double-crested cormorants.

Of the three issues mentioned above, beach grooming is the most controversial. People who have invested significant resources purchasing property on lakes and bays did so with the expectation that their beaches would be there for them to enjoy forever. But the natural world does not always comply with our expectations and, in this case, lower water levels in Lakes Michigan and Huron have led to all kinds of vegetation coming up where once there were sandy or rocky beaches.

Some (but by no means all) waterfront landowners have tried to maintain their beaches by removing vegetation. The problem is that this new habitat is a boon for some species, especially those that have lost inland wetland habitats that disappeared or shrank in size with lower lake levels.

Wildlife that has benefited from these new wetlands include amphibians, reptiles and fish. And birds that will use this kind of habitat include a number of songbirds such as common yellowthroats.

We can all help by refraining from purchasing cypress mulch and by understanding that when cormorant population controls are initiated, they are done so in order to help species that are displaced. And if we own beachfront property that has been affected by lower lake levels, we might just want to appreciate what the resulting new habitat has brought rather than battle with Mother Nature.

Kay Charter is executive director of Saving Birds Thru Habitat, an organization that teaches people how to help migrating birds whose populations are declining.

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