We were enjoying a visit to a lighthouse in South Portland on Maine Open Lighthouse Day recently when a tight flock of about 150 semipalmated sandpipers came wheeling into view and landed on the rocks nearby.

They were almost all juvenile birds that had just migrated down from some location unknown to us in the Arctic, where they had hatched.

This flock was not a large one as flocks of sandpipers and plovers go — they can number in the thousands, sometimes even tens of thousands (or rarer still, hundreds of thousands) in a few highly favored feeding and roosting locations.

Seeing a grand spectacle of bird abundance can be a life-changing experience for many people; in the very least, such flocks leave an impression that is not forgotten.

We still remember the sense of awe we felt when we got to see a million snow geese coming in to roost for the night on the north end of Cayuga Lake in upstate New York.

Or the tens of thousands of swallows (most tree swallows) that swirled in dark clouds in the evening sky of early fall above the marshes of Montezuma National Wildlife Refuge before suddenly pouring down like liquid into the cattails to spend the night.

Or seeing hundreds of thousands of red-necked phalaropes in the waters off Eastport decades ago. Or the hundreds of chimney swifts that chattered over us in Waterville just last year.

Birders have been reporting other spectacles of abundance here in Maine over recent weeks: late-summer flocks of swallows amassing on a wire before heading south; shorebirds in the hundreds or thousands feeding furiously to put on weight for their long migratory flights; common eiders appearing in flocks of hundreds coming south from Canada to spend their winters here with us; warblers and other songbirds descending from their night migration to look for food and safety in woodlands, wetlands, parks and preserves.

It is wonderful and hopeful to see an abundance and diversity of birds right in our own region. But it is something we should never take for granted. We were just perusing a couple of unusual books by Errol Fuller that make it hard to forget the abundance of some of our species.

One of them, called “Lost Animals,” is a collection of the last, and often only, photos of species that are now extinct. It sounds like a downer but there is something compelling and personal about seeing a photographic image capturing a moment in time when the animal was simply going about its daily life. The last known photos of the Eskimo curlew, taken in 1962 in Texas, are shown in the book.

Eskimo curlews were an abundant part of Maine’s avifauna and a species that was taken for food (sometimes in excessively large numbers) along the coast during its fall migration. Fuller’s newest book, “The Passenger Pigeon,” describes the history of another former Maine bird. The passenger pigeon was thought to have once numbered in the billions, and Maine settlers and Native Americans alike must have witnessed the jaw-dropping sight of flocks of millions of birds that sometimes darkened the skies for days.

The 100-year memorial of the passing from the world of the last passenger pigeon was commemorated a few weeks ago. Let’s make sure we take care of our natural world so we don’t have to remember any others from photos alone.

Dr. Jeff Wells is the senior scientist for the Boreal Songbird Initiative. During his time at the famed Cornell Lab of Ornithology and as the Audubon Society's national bird conservation director, Dr. Wells earned a reputation as one of the nation's leading bird experts and conservation biologists. Jeff's grandfather, the late John Chase, was a columnist for the Boothbay Register for many years. Allison Childs Wells, also formerly of the Cornell Lab of Ornithology, is a widely published natural history writer and a senior director at the Natural Resources Council of Maine. Together, they have been writing and teaching people about birds for decades. The Maine natives are authors of the highly acclaimed book, “Maine's Favorite Birds.