There is a small and dwindling population of great cormorants that nest in Midcoast Maine.
These birds, the only great cormorants breeding in the United States, are threatened with extirpation because of their vulnerability to a thriving population of seabird-eating bald eagles.
Great cormorants are elegant, intelligent and widely dispersed. There are populations in Europe, Asia, Africa and Australia. Individuals of the same species have been domesticated for catching fish by some Asian peoples.
Great cormorants are larger than the more familiar shag or double-crested cormorant-they have a white cheek and during the spring a white flank patch. Great cormorants are the ones around during the winter.
I have helped document seabird populations since when as a youth I helped my father Bill Drury with surveys in Maine and Western Alaska.
With the support of Brad Allen, bird group leader at the Maine Department of Inland Fisheries and Wildlife, I have counted the nests of this population from a boat annually since 1983.
In 1944, after noting the then recent expansion of great cormorants breeding range in Nova Scotia, eminent Bowdoin ornithologist Alfred Gross wrote “As yet I have no evidence of their nesting in New England, but since there is a possibility that P. carbo [great cormorants] will continue to extend its breeding range, it is important that we be on the watch for its nesting on the islands of the Maine coast.”
His anticipation was realized in 1983 when we found 46 great cormorant nests at three sites in Jericho Bay, east of Isle au Haut. They were on the Spit at Great Spoon, The White Horse and on the northwestern shore of Little Spoon.
When double-crested cormorants re-colonized Maine around 1900 they first settled on The Black Horse, just south of Little Spoon.
There is something in the geography there that appeals to the cormorant’s sense of a good place to be. The great cormorant population grew steadily until 1992 when there were 260 nests counted at seven sites in Jericho Bay, 176 of which were on Great Spoon and Little Spoon islands.
Whether the individuals that made up the growth of this population were produced by the original pioneers or were additional immigrants is not known-it seems likely that it was some of both.
This population’s luck has changed dramatically. The total number of nests counted during annual surveys declined steadily after 1992. During the last four seasons, there have been fewer than 100 nests counted, and those nests have produced very few young. In 2008 there were a total of 80 nests at seven sites between Vinalhaven and Swan’s Island.
In 1900 the only documented breeding site for this species in North America was Anticosti Island in the Gulf of St. Lawrence. This population, about 5,500 pairs as of 1995, now breeds on the northern shore of the Gulf of St. Lawrence the southern shore of Newfoundland, Prince Edward Island, the Magdalen Islands, Nova Scotia (mostly around Cape Breton) and in Maine.
In Maine, these great cormorants nest on barren islands, some with hundreds of pairs of nesting gulls and eiders. All these birds have been a great source of fodder for the growing eagle population in the area.
One hundred years ago the Maine coastal eagles are reported to have been largely fish-eating. But during recent summers the easiest things for these eagles to catch have been gulls, eiders and cormorants. There are adult seabirds in the spring, eider ducklings in June, and by mid-July, large gull chicks.
This abundance of resources has attracted many young eagles to some islands. On July 24, 2006 there were at least 10 eagles on 25-acre Great Spoon, there were at least 13 eagles there on Aug. 4, 2008. On one-half acre White Horse, there were there were seven eagles on Aug. 30, 2006. There have often been six to eight eagles around Otter and Robert’s islands in Penobscot bay in July and August.
By late August most of the young gulls have dispersed and the clumps of delicious unfledged cormorant chicks become the easiest thing for an eagle to catch. You can tell when eagles have been feeding at a cormorant colony, since the young cormorants who would otherwise be in sibling clumps near their nest platforms are all massed up down by the water.
There they can get overboard in order to try to dodge eagles by diving. Disturbance by eagles likely reduces weight at fledging and thus first winter survival rate of those young cormorants not consumed.
The eagles don’t always wait until the young gulls disperse to attack cormorants. Eagle disturbance caused the cormorants to abandon their nests on The White Horse by July 20 in 2007. In 2008, the colonies at Great Spoon and Green Ledge (Fog Island), together about 30 percent of the breeding population in the U.S., were abandoned by mid-June.
The recent dramatic increase in the number of eagles in the area has changed the landscape for the gulls, eiders and cormorants. The eagles most dramatic effect has been on great cormorants because their population was small to begin with.
Most of the eagles feeding on these islands are young, some might live a long time and many have been broken in eating birds and they will remember that. Short of culling eagles there is not much that people can do in hopes of preventing the loss of this species.
On Seal Island the presence of observers at the research camp there can keep the eagles off and for the last three years the Fish and Wildlife Service has extended the field season past mid-August in part to guard the cormorants. Because of this Seal Island has been the only productive colony for this species in the area. Cormorants are quite willing to change colony site if disturbed, if they are driven from Seal Island it would be much more difficult for people to help protect this population.
Observers arrive on Seal Island in mid-May at least a couple of weeks after great cormorants have started to lay eggs; during this time those eggs are vulnerable to gulls if eagles drive the adults from their nests. This has apparently not happened there yet.
To guard against Eagles driving the cormorants from Seal Island it would be worth the expense of maintaining two observers on the island for a couple of weeks during early May. This may be important to increase the chances that this species is not eliminated as one of the Maine’s breeding birds.
John Drury is seasonal sports columnist for The Wind, Vinalhaven’s weekly newspaper, and lives on Green’s Island and Vinalhaven.