The sun was finally low enough that the heat of the day was starting to ease. We were just about to head home after a pleasant afternoon at the always popular Lake Artemesia Park in College Park, MD.

There had been resident Canada geese and migratory pied-billed grebes on the water. A great blue heron was looking for dinner near the shoreline. Swirling masses of tree swallows ignored the noisy Metro trains racing by. The usual assortment of blue jays and crows were raising a racket. Nothing out of the ordinary, and all of it wonderful.

Just before my wife, Pat, and I hit the road, I noticed a skulking bird in a nearby hedgerow. It was small, but bulky with a big head. Its bold white spectacles told me immediately that I was looking at a blue-headed vireo (Vireo solatarius).

The eponymous head was blue-gray with a thick black bill. A white horizontal streak atop the bill connected to white eye rings, giving the impression that the bird was wearing funky white-framed glasses.

The white of its chin extended underneath all the way to the tail. It had a mossy green back and two white bars on black wings. The sides were faintly yellow.

Males and females look similar, although the females tend to be a bit duller overall.

Blue-headed vireos don’t live around here. The bird was just passing through on its annual migration. They tend to migrate south a bit later than white-eyed vireos. Like red-eyed vireos, you can find blue heads in the Chesapeake region well into October.

These vireos overwinter in a wide coastal area that starts around Norfolk and extends through the Carolinas and into the Gulf states, Mexico and Central America.

In early spring, these medium-distance migrants begin to appear in the Appalachian forests of Georgia. They quickly disperse across the eastern United States, including all of the Chesapeake watershed.

From June through late August, though, they can only be found reliably in the mountains of western Virginia, Maryland and West Virginia. Farther north, the breeding zone expands to include most of Pennsylvania and New York and up through the majority of Canada.

In Canada, blue-headed vireos usually nest in coniferous forests; farther south they also use deciduous forests.

On their breeding grounds, male blue heads pick out a nesting site, usually 5–15 feet above ground. His mate will quickly join him in nest construction before she takes over entirely to put on the finishing touches: lichen, spider webs and rootlets as a soft nest lining.

They will produce a single brood each year of three to six eggs (usually four). Both parents incubate, although the female appears to take all the overnight hours. When the eggs hatch about two weeks later, the chicks are helpless. Oddly, the male then takes over. He alone will feed his offspring during the next two weeks before the nestlings are ready to fledge.

Food during the summer is almost exclusively animal, mostly insects. They also eat spiders and snails. The protein in this food is critical to the growth of the chicks and to prepare the adults for the long journey home at the end of summer.

These birds forage for insects and their larvae in the top half of a tree’s branches. It slowly moves along a branch, carefully inspecting for possible prey after every step. After a short hop or flight to a nearby branch, the methodical gleaning continues.

Although insects make up 95% of the blue-headed vireo’s summer diet, fruits may account for 50% of its winter food.

The blue head is closely related to three sister species: the Cassin’s, Plumbeous and Bell’s vireos. All were once considered a single species called the solitary vireo. Clearer delineation of geographic separation and varied plumages, as well as critical DNA evidence, led to the split. The blue head kept the scientific name for the species, solitarius, while the other species were given new names.

Luckily, the nearly identical Cassin’s vireo does not overlap with the blue head’s range.

The bird I saw at Lake Artemesia was on its way south. Just like spring, the fall sees migrating blue heads spread across the watershed as they make their way to their other habitats.

While migrating, the blue-headed vireo is less selective about the landscape. It still prefers forest to field, but expansive tracts aren’t necessary. As I had just witnessed, sometimes trees aren’t even needed: A hedgerow will occasionally suffice.

It had been a lovely afternoon, and I had been deeply contented. And then, when I least expected it, there was this wonderful surprise: a final surfeit of beauty.

Sometimes the gifts of nature seem boundless. This was one of those times.