Some exotic species adapt well to new environments and become integrated into their new environment; others don't. For those that act in an aggressive manner by out-competing and dominating their native counterparts, the overwhelming impact on the native community is often a significant reduction in biological diversity. We have recently seen three new bird species in the Lake Champlain Basin that have the potential for becoming major wildlife nuisances across Vermont.
Mute swans are large, elegant-looking water birds not native to North America. They were brought to this continent from Europe, and, until recently, there were no wild mute swans in Vermont although there was a small number of captive birds. Wild mute swans have successfully reproduced in at least one Vermont location and they appear to be establishing themselves at other locations.
Mute swans are combative birds known to destroy wetland habitat and to displace native wetland bird species. Several states have documented that this bird is not an asset despite its attractive appearance. At this stage, the population is small enough so its elimination is a practical management action, and we have been advised by our peers in other states to prevent the spread of this species.
The ring-billed gull and double-crested cormorant are native North American birds and their relatively recent expansion into Vermont is a natural occurrence. Their booming populations on a small, state-owned island off the shore of Grand Isle, however, has reached alarming proportions. All trees on Young Island have been stripped of their leaves in recent summers, and other bird species - black-crowned night herons, cattle egret, black and mallard ducks - have been driven away.
In the past several years, ring-billed gulls and cormorants have begun nesting on several other islands and at the mouth of the Missisquoi River. If we do nothing to limit these birds, the plant and wildlife biodiversity of Lake Champlain will likely decline as other islands are colonized.
With public input, the Agency will develop plans to manage the populations of all three bird species consistent with its mission to protect the "integrity, diversity, and vitality of all natural systems."
Other non-native species that have significantly impacted the diversity of native ecosystems include the zebra mussel and a number of plant species, such as Eurasian watermilfoil, water chestnut, purple loosestrife, phragmites, and Japanese knotweed. The Agency is developing a statewide management strategy to identify options and recommend actions for dealing with exotic aquatic species.