The high-pitched, burry squealing of terns reached me on the hill, and I looked down to see squadrons of them patrolling the surf.

Their bodies were dazzling white against the blue-green of the ocean, their flight light and buoyant. Every now and then I saw one pull up short, hover briefly, and plunge straight down like a rock into the sea.

The small splash this created was enough to see even from my distance. A second or two later, the bird erupted from the surface, giving its feathers a ruffle in mid-air and shrugging off the water.

I was too far away to see if its foray into the sea was successful, and the bird just resumed its hunt along with its comrades, tirelessly scanning for unsuspecting fish in the cold shallows of the Atlantic.

Summer wouldn’t be summer for me without the experience of this delicate aerial ballet. I’m not quite sure why I find terns so captivating; maybe it’s their refinement – the sharp, clean lines of body and feather, so different from the large and cumbersome gulls. Or maybe it’s the way they truly seem to ride the ocean breezes, bourn along as lightly as a single feather would be.

Perhaps it is their relative rarity – they are surely not as numerous as gulls nor as pedestrian and obnoxious.

I wasn’t positive – since I didn’t have binoculars with me – but I guessed the terns I was seeing that day were common terns. These birds most often nest on rocky islands that have not been taken over by gulls; they will also nest on beaches, in salt marshes, and in freshwater marshes. They are our most widespread North American tern, breeding throughout much of Canada and parts of the northern United States and the Eastern Seaboard.

Terns, in general, are more specialized in their food habits than gulls. Their diets consist mostly of fish, with some crustaceans, sometimes squid, and even insects. They don’t feed at human refuse sites as will gulls.

Their nests are no more than mere scrapes in the ground, lined with small pebbles and shell fragments and other bits of material. A typical clutch contains three eggs, which is interesting because terns, as well as gulls (and unlike other birds), have three incubation patches as opposed to one.

Chicks are born covered with down and although they can move about soon after, they are vulnerable to the elements and predators. Their parents feed them exclusively until they are about 6 weeks old, after which the young begin to follow them as they search for food.

I believe I witnessed this particular stage in a young tern’s development several days ago. One bird – which I presumed was the parent – flew confidently along the shoreline, making mock dives as if to show its two squawking followers how it was done.

What I assumed to be its two young would follow along, making a racket, before seeming to tire and alighting on the beach, there to sit, wait and watch – and scream for food.

Ornithologists have observed that even when they are able to, young common terns do not fly very much. Their job is to eat and gain weight; by the time migration rolls around, they may weigh more than the adults. Even then, adults may feed them during migration, and continue to do so on their wintering grounds of South America.

As I observed the terns, I imagined them beginning their migration. Taking off across the water, their small, delicate forms would disappear into the sky. They’d be taking summer with them, but at the same time, carrying a promise of many more to come.

BDN bird columnist Chris Corio can be reached at bdnsports@bangordailynews.net