At 9:30 in the morning, the ferry terminal is busy with people coming and going. Through the window, we can see bright white and yellow ferries with red trim, tied to the pier. Their names — Island Romance, Maquoit II and Aucocisco — are painted on the transoms. I am here for a birding trip on Casco Bay Line’s mail boat, eager to spend this unusually warm sunny day on the water, and to see something other than our usual winter yard birds.

Our group begins to show up, dressed in warm jackets, wind pants, hats and carrying binoculars. As each one arrives, the trip leaders from Maine Audubon and the Oceanside Conservation Trust check another name off the list. We pile our gear onto benches, sip hot drinks from white disposable cups, munch on cinnamon rolls or scones from the bakery across the street, and introduce ourselves to each other. Conversations range from local sightings of a West Coast goose, to birding in Costa Rica, but when the loudspeaker comes on to announce that the mail boat is boarding at Gate 3, we collect our gear, head out the door, and file onto the ferry Aucocisco.

Before the boat pulls away from the pier, binoculars are up, and we are scanning rooftops and water for birds. There are gulls galore: great black-backed gulls, the largest gulls in North America, and smaller herring gulls. It takes four years for these gulls to attain full adult plumage, so they vary widely in appearance. When someone spots a pale gray gull with white wingtips, we all rush to look. It is an Iceland gull, a bird found along our coast only in winter, and we take it as a favorable omen for our trip.

The ferry heads out into the harbor, its engine throbbing gently. All around us the dark blue ocean gleams and sparkles in bright sunshine. The Portland skyline spreads out behind us, the Casco Bay islands lie ahead, and to starboard we see Portland Head Light, Spring Point Light and Bug Light. There are birds everywhere on the water. White and black male common eiders, large sea ducks, with a forehead that slopes down onto the bill. Females are brown, but share the same distinctive silhouette. Flocks of long-tailed ducks take flight, and we see the male’s long slender tail feathers that gives this bird its name. We see common loons, still in gray winter plumage. Soon, they will molt into the familiar black and white, and will make reconnaissance flights inland to check on ice conditions on their breeding lakes. In spring, the ice will go out, and loons will appear on the lakes as if by magic, filling the air with their triumphant calls. Today, though, they float silently on the waves, like little gray battleships.

At each island, the crew offloads and collects mail. We discharge a few passengers and take on others, but it is more fun watching the dogs, whose enthusiasm is contagious. Released from the confines of the ferry the dogs leap joyfully along the wharf, and everyone smiles. Disembarking passengers, on their way to island homes, lug canvas bags bulging with stuff. They struggle with wheeled carts loaded with supplies, carrying everything from big packages of paper towels to long wands of foam pipe insulation. On a few islands, they load their baggage into a pickup truck, but not every island provides such luxurious transportation. At each stop, we look for birds, and as the ferry pulls away from one wharf, little bufflehead ducks dive and pop up, again and again. At another stop, we admire a strikingly handsome male red-breasted merganser escorting his mate through a small cove. Two common murres, seabirds occasionally seen in winter on coastal waters, are an unexpected bonus. In summer, they can be seen only around rocky outer islands, where they nest. We pass an island with lovely sand beaches, and the ferry captain points out a huge eagle’s nest at the top of a tall red spruce tree. We see horned grebes, a red-tailed hawk, more common eiders, surf scoters, and an immature bald eagle. We wonder how many common loons we have seen today, and guess at least 50, maybe more.

On the return trip, the boat stops at a few more islands, but before we know it three hours have passed and we are back in the harbor, tying up to the terminal pier. Today, we have seen magnificent scenery and lighthouses, have had a peek into island life, and have even had a chance to get off the ferry for a few minutes to walk around an island village. Birds were everywhere, perched on piers and rocks, diving, flying, and simply resting on the water. It was a fine day for an ocean cruise.