Swans and purple loosestrife

By CONNIE MERTZ

We view the mute swan as a species of beauty and grace, but in some parts of the East, their presence brings concern. It never was a native species here, but was imported from Eurasia in the late 1800’s. Mostly limited to private ponds, they added a touch of loveliness. In the early 1960’s, five escaped into the wild, and they have been multiplying ever since.

Estimated to number 4,000 in the Chesapeake Bay region alone, their numbers have surged because the birds lack natural enemies to bring balance to the population. What started as a prize bird has now turned into an unwanted pest. They are known to destroy nests and chicks of terns and skimmers, both threatened species in Maryland. It may not be done intentionally by the swans, but on their wanderings, they just crush whatever is underfoot. They also consume submerged grasses, necessary for other waterfowl species, fish and crabs. In fact, swan populations are known to consume nine million pounds of underwater grasses every year.

Another unwanted species more common than the mute swan is the plant, purple loosestrife. Here again, it is an imported species, brought over in the 1800’s from Europe; it too has no natural enemy to keep it under control. One purple loosestrife plant can produce over a million seeds. Wind, water, animals and humans easily disperse the tiny seeds. It not only chokes out other plants, its dense root system blocks the free flowing water from wetlands and waterways, forcing costly dredging.

There is no easy solution to bring these invaders and others like them, such as the water chestnut and zebra mussel, under control.