Harbor seals are the fickle marquee headliners of the NYC Audubon’s Winter Seals and Waterbirds of NY Harbor Ecocruise.

The seasonal Sunday tour cruises near Swinburne Island — a man-made heap of rubble in our lower harbor that once served as a quarantine center for immigrants — to catch sight of the marine mammals, plus various birds, in our waters this time of year.

“I try not to mention seals,” says guide Gabriel Willow. “I’m a little superstitious.”

Still, on a recent ecocruise aboard a New York Water Taxi, a small colony of the plump pinnipeds could be seen cavorting like goofy Labrador retrievers in the water off Swinburne while another seal lay on a crashed piece of concrete like a giant puffer fish.

One of the challenges of peeping wildlife in urban environments, concedes Willow, is discerning, “Is it garbage or is it an animal?”

The seals have a limited engagement in our harbor and will be gone by April, on their way to mate in and around Maine, so the winter cruise is one of the only ways for boat-free, nature-craving New Yorkers to see them.

Winter is also the only time to see great cormorants, brant geese and ducks such as greater scaups, buffleheads, long-tailed ducks, the American Black Duck, the common goldeneye and red breasted mergansers. Peregrine falcons may also be seen nesting in the Verrazano-Narrows Bridge, a “wilderness habitat,” Willow notes.

The presence of the harbor seals is a tiny triumph of nature in our increasingly crowded and complicated city, showing that the water of New York Harbor “is not as polluted as it used to be,” says Willow, and that fish like shad or herring are present in force, serving as the seals’ Sunday brunch.

“The Hudson River is much cleaner than it was in the mid-20th century, and, in some ways, [cleaner] than in the 1800s” when it was conscripted into use as a giant sewer, Willow explains.

Beyond the lesson in the harbor wildlife, the tour gives a history of the area: Upper Manhattan and the Bronx are the geologic elders of our region, while Brooklyn, Queens and Staten Island formed only after a phalanx of glaciers excreted the younger boroughs as they lumbered over our region.

The winter tours on the water are nippy, but in the interior of the double decker New York Water Taxi, free hot chocolate and tea are served. And to help distinguish the seals from the rocks, the Audubon lends cruise participants binoculars.