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BIRDS of the Lower Penobscot River

Jeff Wells and Catherine Schmitt

The Penobscot River is a popular location for birdwatching because it hosts a great number and diversity of species throughout the year. Many parts of the river attract concentrations of migratory and wintering waterfowl including one of the state's largest concentrations of the rather rare eastern population of Barrow's goldeneyes (Meehan 2002), and under certain weather conditions in spring, large numbers of common eiders appear on the river as they make their way along what may be the only inland migration route in the world of this otherwise marine species. Other wintering waterfowl include black ducks, greater scaup, buffleheads, mergansers, and scoters (Hartman 1960). The watershed supplies vital foraging and breeding habitat for cormorants, bald eagles, osprey, great blue herons, green herons, belted kingfishers, and many other species. Throughout the season, concentrations of spawning fish are attended by a variety of fish-eating bird species, sometimes in significant numbers including concentrations of certain species rarely seen at other times and places, such as bald eagles and osprey.

Hatches of insects from aquatic larval stages to aerial adult stages (stoneflies, mayflies) are opportunistically foraged upon by many species as varied as gulls, swallows, waxwings, and warblers. When these hatches occur during migratory periods or periods of cool weather when terrestrial insects are less available, they provide crucial food supplies without which many bird species would suffer increased mortality and/or reduced reproductive output. Marsh and shoreline habitats along the river are used in migration by shorebirds (solitary sandpiper, spotted sandpiper, greater and lesser yellowlegs, least sandpiper, Wilson's snipe), waterfowl (mallard, American black duck, green-winged teal), rails (sora, Virginia rail), and herons (great blue heron, green heron, American bittern). Some of these species also use these marsh and shoreline habitats during the breeding season.

The various bird species that use the river, bay, and adjacent habitats can be partitioned into several ecological or indicator groups based on foraging ecology in relation especially to other animal and plant communities in or adjacent to the water.

Fish-eating species

common merganser, double-crested cormorant , great cormorant, great blue heron , green heron, osprey, bald eagle , various gulls, belted kingfisher, guillemot

Cormorants

Double-crested cormorants love to hang out near the dams on the Penobscot, where they lounge in the sun, pluck fish from the spillways, hang their wings out to dry, and yell at each other. Fishermen have never been fans of these piscivorous (fish-eating) birds, which were extirpated from New England coastlines in the 1800s. Cormorants were regularly harassed and killed until 1972 when the Migratory Bird Treaty was amended to protect them. The population in Maine gradually increased to 28,000 breeding pairs by the end of the twentieth century. Larger populations and their expanded range have revived questions about how many fish cormorants eat, and how they might be affecting struggling Atlantic salmon populations. In 2004, Maine's U.S. Senators Snowe and Collins requested $200,000 "to combat the adverse impacts of the double-crested cormorant on ongoing efforts to restore Atlantic salmon in Maine's waters." Because fish tend to collect below the dams, offering fast food for cormorants, dam removal may help to disperse fish throughout the river and make meals less readily available for cormorants and other piscivores ( Blackwell and Sinclair 1995 ; Krohn et al. 1995 ; Blackwell and Krohn 1997 ).

In a study of mercury levels in Gulf of Maine seabirds, cormorant eggs and juveniles were relatively higher in mercury than other seabirds, although levels were below safety thresholds ( Goodale et al. 2006 ).

Links:

Research from the Maine Cooperative Fish and Wildlife Research Unit

http://www.wle.umaine.edu/fac/krohn/cormorant.html

Bald Eagles

Bald eagles are a common sight on the Penobscot today. Coastal territories may be occupied year-round, while birds from inland sites disperse in fall and return in March.

While the bald eagle population has made a comeback, reproduction rates are still low in Maine, mainly because of chemical contamination of their food web. Eagles have been monitored by Maine Audubon and state and federal fish and wildlife agencies since 1962, and monitoring became more extensive and rigorous after the species was placed on the Endangered Species List in 1978. After listing, the breeding range and number of nesting pairs slowly increased throughout the state.

Maine Department of Inland Fisheries & Wildlife annually monitors the distribution and abundance (in April), and productivity (in June) of bald eagle nests. In 1986, there were 85 nesting pairs of bald eagles in Maine; 10 of them were in Penobscot Bay ( Woodward et al. 1986 ). Today, the number of nesting pairs has increased to 385 statewide and around 80 eagle nesting areas in the Penobscot watershed. Maine ranks eighth in abundance of breeding eagles among the lower 48 states and is the stronghold for the species in the northeastern U.S.

In addition, data from 1976-1981 are available on bald eagle food habits. These data showed that fish (brown bullhead, white sucker, and chain pickerel) comprised 77 percent of inland eagle diets, and birds (black duck, gulls, cormorant, eider) accounted for 76% of coastal bird diets. Alewives and blueback herring were common food items for inshore coastal (estuarine) nests ( Todd et al. 1982 ) .

Productivity of nesting pairs in Maine is below recovery goals, partly as a result of persistent organic chlorine compounds like PCBs and DDE (a derivative of DDT) which are still at unsafe levels ( Mierzykowsli and Carr 2002 ), as well as mercury ( DeSorbo and Evers 2006 ) Mercury in bald eagles are monitored by the BioDiversity Research Institute (see Figure 1).

Great Blue Heron

  A frequent visitor to the marshes and wetlands of the lower Penobscot River, the great blue heron nests in colonies (250 or less nests per colony). Approximately 25 percent of the entire Atlantic coast population of great blue herons nests along the Maine coast between Casco Bay and Machias Bay ( Custer and Osborn 1977 ). Colonies are formed on remote, densely forested marine islands where herons typically build large twig nests in the tops of spruce trees ( Gibbs et al. 1988 ). Maine Department of Inland Fisheries and Wildlife is currently in the process of updating historical surveys of heron colonies (e.g., Woodward et al. 1986 ).

Osprey

Osprey nest in Maine in spring and summer and fly south in late summer and fall.

Unlike eagles, who catch fish at the water surface, osprey are able to catch fish deeper in the water with their long, sharp talons. An osprey will hover up to 100 feet above the water before diving at 80 miles per hour to catch fish beneath the water surface.

Ospreys have a wingspan of five to six feet and are easily recognizable in the air by their bent wings. Ospreys live close to (within one kilometer of) large bodies of water including the Penobscot river, estuary, and bay.

Ospreys dine on fish almost exclusively and make their large stick nests in trees, cliffs, power line towers, billboards, and any other tall structure. Ospreys return to the same nesting site year after year, and Maine Department of Inland Fisheries and Wildlife tracks nest locations. Ospreys in the Penobscot watershed are threatened by PCBs and mercury contamination .

Guillemots

The black guillemot ( Cepphus grylle) is a common, pigeon-sized seabird that nests in burrows among the rocks of Maine coastal islands. In late summer, guillemots lose their summer breeding plumage (black with white wing patches) and change to a mottled gray and brown. Found from the Arctic Circle as far south as Maine, the guillemot is our most nearshore member of the Auk family, which also includes puffins and murres. These birds fly underwater for long distances, and serve the same ecological niche as penguins in the Southern Hemisphere. Guillemots eat rock gunnel, a benthic fish. Mercury levels in eggs and blood from Penobscot Bay guillemots were higher than other seabirds in the region ( Goodale et al. 2006 ).

Mergansers

Common mergansers ( Mergus merganser ) are frequent visitors to the Penobscot river, estuary, bay, and area lakes. A large diving duck, the common merganser has a long thin orange bill with toothy projections along its edges that help the duck hold onto its slippery fish prey. The red-breasted merganser ( Mergus serrator ) occurs more frequently in the estuary and bay, typically nests on the ground, and has dark-colored down.

Terns 

Common terns, black terns, least terns, arctic terns, Caspian tern, roseate tern, and Forster's tern have all been seen in Maine. In 1984 the Maine Audubon Society and U.S. Fish and Wildlife Service removed gulls from a large segment of Seal Island in Penobscot Bay as part of a project to attract Atlantic puffins and other seabird species to the area. In 1989, arctic terns first nested on Seal Island, and numbers increased to a high of approximately 500 pairs in 1995 ( Anderson and Devlin 1999 ). Matinicus Rock and Metintic Islands are two tern restoration sites also in Penobscot Bay.

Aquatic invertebrate specialists feeders

bufflehead, common goldeneye, Barrow's goldeneye, some gulls, various shorebird/sandpipers, American black duck

Barrow's Goldeneye 

Barrow's goldeneye is a medium-sized diving duck. More the 90% of the world's population breeds from central Alaska to northern California, however there is a small population that is concentrated along the St. Lawrence river in eastern North America. They do not breed in Maine, but roughly 250 birds from the Canadian population winter along the Maine coast, including on the lower Penobscot River and Belfast Bay. The Barrow's goldeneye is listed as a threatened species in Maine. In salt water, they eat mollusks; in fresh water, they eat insects, fish eggs, mollusks, crustaceans, and plants ( Meehan 2002 ).

Common Eider 

Eiders are year-round residents in Maine's coastal waters, and come spring they nest on several Penobscot Bay islands. After the females are settled on their eggs, males migrate to traditional sites in late June and July to molt. During this molting period, which lasts about a month, the adult birds congregate by the thousands. Large numbers provide safety while the birds lose their feathers and are rendered flightless and vulnerable to predation for four weeks.

Eiders and their eggs provided food for Native Americans and early colonists. By the late 1800s, eiders were nearly extirpated from their nesting islands due to hunting and egg collection (Allen 2000).

In 1895, ornithologist Ora W. Knight of Bangor noted eider nests near Isle au Haut:

"On June 26, 1895, I found three nests with eggs of the American eider on Spirit Ledge, a small island about five miles from Isle au Haut, Maine. The nests were placed on the ground in the midst of a clump of umbelliferous plants [ Heracleum lanatum ], which were growing near the center of the island, and contained two fresh eggs, and incubated sets of three and six eggs respectively. The two latter nests were found by flushing the females. Later in the day I found a fourth nest, containing four eggs, on Saddleback Ledge, about three miles distant from Spirit Ledge. This last nest was on the ground in plain sight, but the eggs were hidden by a thick covering of down…The captain of the boat which conveyed me to the islands informed me that the fishermen considered the eggs a great delicacy, and collected them for cooking purposes. He also informed me that the 'Sea Ducks,' as he called them, used to nest in much greater numbers near Isle au Haut, but that the constant persecutions of the fishermen had lately caused the birds to nest on the ledges in greatly reduced numbers."

By the early 20th century, laws and regulations were enacted to protect seabirds and the eider population began to rebuild.

A 1967 study documented over 1,000 eider nests on Penobscot Bay islands ( Choate 1967 ). Females are faithful to their natal and breeding areas and frequently reuse the same island nest site. Common Eiders are diurnal feeders and dive to pick mollusks and crustaceans from the sea bottom in water depths generally ranging from 10 to 20 meters.

American Black Duck

Black ducks eat macoma and soft-shell clams from the mud on the river bottom. As many as 5,000 black ducks have wintered in the Penobscot estuary between Winterport and Sandy Point ( Hartman 1963 ).

Harlequin Duck

About 200 harlequin ducks winter along the southern shore of Isle au Haut, between Western and Eastern heads. Harlequin ducks feed on amphipods and other invertebrates on the wave-exposed shoreline. Another 200-300 winter around surrounding islands, including the Cowpens , Little Spoon, Great Spoon, and York Islands ( MNAP ).

Aerial insectivores

swallows, cedar waxwings

Terrestrial insectivores

various migrant and breeding landbirds

Aquatic herbivores

mallard, green-winged teal, hooded merganser, wood duck

Marsh inhabiting species

rails, herons

Over 180 bird species have been identified in Penjajawoc Marsh, part of the Caribou Bog complex, including many rare species of wading and marsh birds such as least bittern, American bittern, sora, pied-billed grebe, and the Virginia rail. Bobolinks nest in nearby grasslands.

The sedge wren and yellow rail have been documented in Sunkhaze Meadows.

The saltmarsh sharp-tailed sparrow ( Ammodramus caudacutus ) reaches the northern extent of its range at the Weskeag River estuary in South Thomaston (Hodgman et al. 2002). Nelson's sharp-tailed sparrow ( Ammodramus nelsoni ) inhabits brackish marshes. Both of these species are of high conservation priority in the northeastern United States, and are vulnerable to mercury pollution.