It was a perfect day at the beach. The temperature was hot enough to make swimming enjoyable. The water was a vibrant blue-green. And from the hazy blue sky dotted with clouds, terns wheeled, banked and dove into the ocean after fish.

I was first alerted to their presence by their brief, high-pitched “kip” calls as they flew overhead. Looking up from my beach blanket, I saw them slicing gracefully through the air, making hairpin turns and plummeting with dizzying speed and suddenness into the water. It was amazing to watch them disappear completely for a second after splashdown, then take to the sky again as if the interface with air and water wasn’t a barrier to them in the slightest.

It was amusing, too, to watch them shake the water from their feathers mid-flight without missing a wing-beat.

It seemed likely to me that the terns were after the schools of very small fish I had been seeing close to shore. I waded out waist-deep to see if the terns were actually catching any of the fish, but I was never able to determine this. The fish were either too small or being swallowed too quickly for me to observe. I did, however, get fantastic views of the terns as they zipped overhead.

I was able to determine they were common terns, due mainly to their black-tipped, bright, red beaks, but also by their charcoal-gray wings and white underbodies. Arctic terns, which are similar, lack the black tips on their beaks and have more gray on their bodies than do common terns.

Common terns breed on coastal islands from Atlantic Canada to South Carolina, and on islands of inland lakes throughout much of Canada and portions of the northern U.S. Their nests are hardly more than scrapes on the ground, usually in gravel, sand or ground-up shells. Terns are for the most part monogamous, and pairs may remain together for several years. According to “The Birds of North America” species account, the longest recorded pair bond among common terns is 14 years.

I’ll never forget the first time I heard first-hand information about tern breeding habits. It was during a visit to Machias Seal Island near the Bay of Fundy. We had gone out with a charter company that had special permits to bring people to the protected and managed island. The trip itself was an adventure; the island has no dock, so the boat — which I remember being not much larger than a lobster boat — anchored offshore and we had to climb down a ladder into a rowboat and be ferried to the island, where we clambered out onto slippery, seaweed-covered rocks. Then, we had to walk across a narrow plank of wood that spanned a six-foot chasm between rocky ledges.

Conditions had to be just right; if the sea was too rough, there was no going ashore and birders had to be content with observing from the boat.

But I digress. As we were rowed over to the island, a wildlife biologist told us terns exhibited a high amount of “mate fidelity,” but that sometimes, “divorces” occur. That was the first time I had ever heard this term applied to birds, of any species.

Since then, I’ve realized biologists and ornithologists sometimes like to wax poetic about their subjects. Which is refreshing. At the very least, they enjoy using whimsical terms—such as “The Birds of North America” does when it describes the nest-selection process of common terns. After the male selects the territory, he will join his mate in making exploratory scrapes before settling on a nest site. This is dubbed “house-hunting.”

According to “The Birds of North America,” in the Gulf of Maine common terns lay their eggs at the end of May. Incubation may last up to 33 days; chicks fledge the nest when they near 29 days old. So it won’t be too long before the young begin to follow their parents to their feeding areas. I hope they’ll return to my cove and that I’ll have many more perfect summer days in which to observe them.