SMYRNA — Whether it followed a star east or simply wanted to dabble in Delaware waters, a wandering sandhill crane evoked more than a little wondrous joy in a group of birders participating in last week’s 75th Annual Bombay Hook Christmas Bird Count.

The rare sighting at Bombay Hook National Wildlife Refuge of a bird that normally hangs out in the West, had young and old exclaiming “wow!” and sharing spotting scopes to get a better view of the gray mound hunkered down in grass on the other side of Raymond Pool.

The vagabond seemed unperturbed by the gaggle of bird counters across the way as it slowly stretched its neck before resuming its task, perhaps browsing for a midmorning snack.

The last time lifelong birder Andy Ednie of Claymont, compiler for the Bombay Hook circle of the annual Christmas Bird Count, saw a sandhill crane there was on his first visit to the refuge, at the 1969 Christmas count. He was 13 or 14. These days, he roams Bombay Hook almost weekly.

The Dec. 14 event was one of more than 2,300 surveys around the world that takes place between Dec. 14 and Jan. 5, 2015, as part of the 115th Annual Audubon Christmas Bird Count.

Delaware was one of the first states to hold a Christmas count, according to Mr. Ednie. That one took place in Rehoboth Beach in 1907.

The count is the longest-running citizen-science survey in the world, according to the Audubon Society, and collects data that allows researchers to determine the status of bird health, changing populations and environmental impact.

“The goal is to get a snapshot, to determine the diversity of species ... how many types of birds are utilizing the habitat,” said Derek Stoner, of Lancaster, Pennsylvania. Mr. Stoner, of the Delaware Nature Society, and members of the Delaware Dunlins Youth Birders Club of the Delmarva Ornithological Society, of which he is coordinator, were among those participating in the Bombay Hook count. The Bombay Hook count is one of five sponsored by the society.

To get that snapshot, volunteers follow specified routes through a designated 15-mile radius circle, counting the birds they see or hear all day. The Bombay Hook circle, centered at Leipsic, is divided into eight areas, with each having a separate leader.

“Their job is to count every bird and as many different species in that area for the count circle,” said Mr. Ednie, the leader for the refuge section of the circle.

The circles — unchanged over a period of years — result in a “better longitudinal study” as opposed to counting randomly, Mr. Ednie said. And, the census is taken at the same time every year, which also aids in monitoring fluctuating populations.

“Some birds increase,” he said, but overall “more birds are decreasing.”

One example of the latter concern is the American kestrel, which has “all but disappeared.”

Scientists aren’t sure why, but Mr. Ednie offered a couple of theories. Some people point to the growing numbers of Cooper’s hawk, a predator of the kestrel, while others speculate that the practice of spraying newly plowed fields kills grasshoppers, a primary food source for the kestrel.

The youth brigade

Age-wise, Andy Dunn, 12, of Smyrna has Mr. Ednie beat when it comes to first visits to Bombay Hook.

“He’s been coming since before he could walk,” said Andy’s dad, John Dunn. “He came in a car seat.”

The father and son arrived at Bombay Hook count thinking they might see snowy owls again as they did during the 2013 count. A better dining menu in Delmarva perhaps lured the Arctic owls south last year, called an eruption.

“Some have seen them again,” Mr. Dunn said.

Instead, the group spotted the sandhill crane.

“It’s been here for a few months,” Mr. Stoner said. “It’s like a big treasure hunt (and while the count) is about trying to observe as many as you can, to see something like this, it’s always a prize.”

A prize, indeed, because it meant many of the birders could add another species to their life lists.

At 12, Andy’s is 302. He excitedly described No. 300, a mourning warbler he spotted in New York. He said he’s been birding “forever.”

The Delaware Dunlins club gives members like Andy ample opportunity to build their life lists as they take field trips around Delmarva. They recently went to Conowingo Dam in Maryland where they watched eagles feasting on fish chopped up in the dam.

“Sushi for eagles,” said Judy Montgomery of West Grove, Pennsylvania, also with the Delaware Nature Society and the Delaware Dunlins. Both she and Mr. Stoner work at the Ashland Nature Center in Hockessin.

Participating in the count alongside experienced adults like Mr. Stoner, Ms. Montgomery, Mr. Ednie and others benefits the younger birders, according to Mr. Dunn.

“This is like Little League people learning from Cal Ripken and Derek Jeter,” he said.

But even Little League has power hitters. Take Kathleen O’Neil, of Wilmington, for example. The 14-year-old’s life list is “534, maybe.”

“For their age, these are the best birders,” said Mr. Dunn. “Adults often will say ‘I wish I had started when I was their age.’ ”

Mr. Dunn, a lifelong birder, passed along his fascination to his son.

For Amy O’Neil, Kathleen’s mom, it was her mother-in-law who “got me into it 20 years ago.

“Grammy started it.” She smiled at her daughter.

But the Krishnamurthy family of Wilmington pointed to son Arun as the one who got them involved in the Bombay Hook Christmas Count. The 9-year-old started birding five years ago.

“I saw a heron on someone’s roof and became interested,” he said.

That fall he and his parents, Kate and Vikram Krishnamurthy, came to the Christmas count and have returned every year since, along with daughter Bailey, 7.

Like Arun, Mr. Stoner was 4 when he first visited Bombay Hook. That was 32 years ago and he has participated in the count for 12 years.

Back to business

The Sunday count began with divvying up species, with one person counting tundra swans, another Northern pintail ducks and a third Northern shovelers. Ditto for the hawks – Cooper’s and sharp-shinned – and the other birds perched and paddling about the refuge.

A counter explained the process to a novice: An area is divided visually into sections, the person counts heads in that section and then multiplies that figure by the number of sections. Later, Mr. Ednie reviewed the tallies and added up the counts for the day.

While counting, the birders swapped stories, tossed about trivia and answered pop quizzes. What’s the only bird with Delaware as part of its name, Mr. Stoner asked the Delaware Dunlins. A dunlin, by the way, is a shorebird.

The answer rests in the ring-billed gull’s official Latin name. The Larus delawarensis is the most common gull in Delaware, Mr. Stoner said. “It’s the classic parking-lot gull, the fast-food gull.”

The birders laughed, but Andy, pulling out a field guide to look up the Latin name, backed up Mr. Stoner. “It really does say French fry gull.

“I’ve fed them French fries at a McDonald’s,” the 12-year-old said, validating the gull’s nickname. “If you have food in your hand, they will eat it.”

And not just gulls can be hand-fed, he added. “I had a Downy woodpecker eat sunflower seed from my hand.” He stretched out his hand, palm up, to demonstrate.

His recommended field guild for novice birders, regardless of their age, is the “Young Birders Guide to Birds of Eastern North America.”

His father also suggested “The Crossley ID Guide: Eastern Birds.” Its strength, he said, is that it includes multiple images of a species in various stages and environments.

Victorious eagles

Even a rookie birder, however, didn’t need a field guild to identify any of the numerous bald eagles spotted during the count, from three perched on distant snags to a young adult surveying the refuge from a berry-laden tree to those settled in nests in the trees at Shearness Pond.

At Shearness, Ms. Montgomery counted seven grouped around nests. “It’s a good day,” she said, encouraging a stranger to look through her compact but powerful scope at the United States’ national bird.

The numerous snow geese might be one reason for the proliferation of eagles at Bombay Hook. Eagles prey on snow geese.

“The bald eagles were having a good time this morning chasing the snow geese around,” said Mr. Ednie, who began his day at 4 a.m. counting owls in the refuge.

“Years ago you might see one pair of eagles,” said veteran birder Joe Russell, of Newark.

“Today, we counted 13. They have exploded since DDT went away.”

Four decades ago, the eagle was in danger of extinction, according to the U.S. Fish & Wildlife Service, in large part because the pesticide DDT contaminated its food source. The federal government banned the use of DDT in 1972.

The result: Nesting pairs went from less than 500 in 1963 to more than 9,500 in 2007, according to the government agency.

Another population explosion not welcomed so cheerfully is snow goose. It’s gone from 10,000 a few decades ago to 200,000, Mr. Ednie said. One purpose of the count is to monitor the snow goose numbers and weigh the impact on the environment.

Evidence of how the snow geese are changing Bombay Hook is the Leatherberry Flats area opposite Shearness, created by “snow geese eating salt marsh grass and, through many years of chewing grass, exposed the mud flat,” said Mr. Stoner. “It’s an incredible new environment.”

It went from being a typical Delaware marsh to 100 acres of mud flats, he said. Loss of marshes is worrisome because they provide needed buffers from storm surge from the Delaware Bay.

The thrill of the search

In the 19th century, Christmas traditions included the “Side Hunt,” when visitors would square off into teams that would take to fields and woods with loaded guns. At the end of the hunt, the team with the most spoils was declared hunt victor.

In 1900, as the conservation movement took flight and as scientists fretted about declining bird populations, ornithologist Frank Chapman organized what became the first Christmas Bird Count.

The original 27 census takers compiled a count of around 90 species, according to the Audubon Society.

Putting aside the importance of the data gathered, the Christmas Bird Count retains elements of a contest in an individual sense, but instead of carrying guns the hunters sport binoculars, scopes and cameras.

And part of the day’s fun is to see how many different species one can count in one day. The most Mr. Ednie has spotted in Delaware in one day is 199.

The rarest bird he spotted during a Christmas count was a Northern lapwing, a European shorebird related to the killdeer, in 2000.

Then there are those life lists and year lists. Mr. Russell’s life list is “over 500 ... not bad since I haven’t been out West.”

On Sunday the Marine veteran was on a mission to add to his year list for species sighted in Delaware and one bird in particular that has eluded him this year.

“My bittern curse,” Mr. Russell said. “I can’t find them this year. It’s driving me crazy.”

The weather was not quite as sunny and warm as forecast, stalled in the upper 30s for most of the morning with a smidgen of a breeze. Mr. Russell and Mr. Ednie were philosophical, though. The longtime birding companions recalled worse days.

“I have been here when it was 16 degrees and snowing,” said Mr. Ednie.

Arriving at Bear Swamp, another group of counters pointed to the nearly head-high marsh grass along the road where they had spotted a bittern, a furtive heron.

“This could be a miracle,” Mr. Russell said as he eagerly headed toward the grass. He clapped his hands, but failed to flush the bird from its hiding place. “Dang thing probably is freezing, it won’t move.”

It must have moved for somebody, however. Mr. Ednie later confirmed a sighting of a least bittern at Bear Swamp, but not whether Mr. Russell got his Christmas count miracle.