How many Maine people know, we wonder, that there are two species of cormorant that occur regularly in the state? If they do know that both double-crested cormorants and great cormorants occur here, do they know how to tell them apart?

We were musing about that because we spotted an immature great cormorant while walking our dog down along the river at Gardiner Waterfront Park on a recent rather balmy November late afternoon. We were able to tell it was an Immature great cormorant because of its white lower belly contrasting with its gray-brown chest and neck. Immature double-crested cormorants, on the other hand, have the opposite pattern—a pale throat and breast and a darker belly. Great cormorants are also bigger with a chunkier head, and they have a yellow versus orange throat poach border with white chin. Adults in breeding plumage also have white patches on the flanks.

During the summer, double-crested cormorants vastly outnumber their larger relatives. The only place in Maine that you would normally see a great cormorant at that time of year is on or near one of the outer islands where a few nest—the southernmost North American breeding locations of the species.

But in fall, double-crested cormorants migrate south for warmer climes, whereas great cormorants from breeding locations farther north come south to Maine. Most cormorants that you see in the dead of winter are great cormorants, although with milder winter temperatures, occasional and increasing numbers of double-crested cormorants may be found.

Still, the general rule of thumb still applies for now—that in winter, if you see a cormorant, its more likely a great cormorant.

Despite being otherwise quite coastal in distribution, a few, usually immature, great cormorants have been found along Maine’s larger rivers and lakes especially during fall migration. Some have even been found in mid-winter in recent years along the Kennebec River in the Augusta-Gardiner area and on the Penobscot around Bangor. We’ve seen them standing on the edge of the ice near the bit of open water caused by the outflow of the Cobboseecontee Stream into the Kennebec RIver in Gardiner, behind them stretching the blank white expanse of otherwise ice-covered river.

Doing a little digging in the Birds of the World, we were surprised to discover that the Eurasian, African, and Australian subspecies of great cormorant occur widely at inland freshwater locations. Only the subspecies of great cormorant that breeds from Maine north to Greenland and over to northern Europe, is so strictly coastal.

Captive great cormorants were used from ancient times, in China and Japan, to catch fish for their human handlers. The birds were fitted with a harness and then had a ring or strap placed around the throat that prevented them from swallowing large fish.

Ebird data show a widespread decrease in numbers of great cormorants during the non-breeding season across most of their North American range since 2011. Given that other seabird species that overlap in range have also shown widespread declines including herring and great black-backed gulls, it seems likely that ocean warming caused by climate change may be implicated.

Jeffrey V. Wells, Ph.D., is a Fellow of the Cornell Lab of Ornithology and Vice President of Boreal Conservation for National Audubon. Dr. Wells is one of the nation's leading bird experts and conservation biologists. He is a coauthor of the seminal “Birds of Maine” book and author of the “Birder’s Conservation Handbook.” His grandfather, the late John Chase, was a columnist for the Boothbay Register for many years. Allison Childs Wells, formerly of the Cornell Lab of Ornithology, is a senior director at the Natural Resources Council of Maine, a nonprofit membership organization working statewide to protect the nature of Maine. Both are widely published natural history writers and are the authors of the popular books, “Maine’s Favorite Birds” (Tilbury House) and “Birds of Aruba, Bonaire, and Curaçao: A Site and Field Guide,” (Cornell University Press).