From the Winter 2026 concern of Dwelling Chook journal. Subscribe now.
On Maine’s greater than 4,000 offshore islands, winter brings biting winds, waves that crash into snow-draped rocks, and sudden storms that sweep in from the ocean. Ice clings to shrubs and branches, and with the solar setting early, sunlight hours are temporary beneath a constantly overcast sky. It’s a panorama that challenges each folks and wildlife.
And but, flocks of 1 tiny shorebird could be seen right here each winter, hopping round icy coves and salt-swept rocks searching for meals.
“I’ve a variety of respect for Purple Sandpipers,” says Elliot Johnston, an ecologist on the Maine Pure Historical past Observatory who has studied the state’s inhabitants of those birds since 2018. “They’re a very hardy shorebird.”
However Johnston and different scientists are noticing a marked decline among the many Purple Sandpipers that winter alongside the Maine coast. Statewide surveys present the flocks are down greater than 50% versus their numbers 20 years in the past. A brand new research revealed within the journal Ornithology final July, and led by Johnston, might present a clue to the decline—the wintertime weight-reduction plan of Purple Sandpipers within the state, lengthy considered principally blue mussels, now appears to consist principally of barnacles.
In line with Johnston, the research is a key to understanding the conservation outlook for these robust sandpipers that make their winter residence farther north than another shorebird species.
“It’s vital to know, if they’re declining, what’s driving it,” says Johnston. “Weight-reduction plan may probably play a job, particularly for species wintering thus far north.”
Within the early 2000s, a crew of scientists from the Maine Division of Inland Fisheries and Wildlife and Acadia Nationwide Park performed the primary systematic survey of Maine’s coast to doc the total scope of the place these birds are discovered and to check their winter ecology. When the researchers repeated the surveys within the 2010s, in areas the place they’d discovered the very best densities of the birds, they discovered the inhabitants had dropped from about 4,700 Purple Sandpipers to an annual common of round 2,100 sandpipers.
Ecologist Glen Mittelhauser has seen the drop-off in Purple Sandpipers firsthand. He’s been conducting wintertime coastal fowl counts for greater than 40 years, beginning with chartering rides out to sea with skilled Maine fishermen on days when the climate wasn’t too tough. Mittelhauser based the Maine Pure Historical past Observatory as a science-based nonprofit group to observe modifications in Maine’s plant and wildlife populations. Nowadays, he sees far fewer of the diminutive, hardy sandpipers that he so admires—shimmering, he says, with a violet sheen when seen up shut.
“These tiny little issues … they’d be roosting within the solar all day, although it was winter and depraved chilly,” Mittelhauser says. “Now, it’s completely different. … I keep in mind seeing a flock of 1,000 birds again within the ’80s and ’90s. Positively don’t run into these anymore.”
The marine environments alongside the Maine coast have additionally modified lots over the previous few many years. In line with the Gulf of Maine Analysis Institute, sea floor temperatures within the Gulf of Maine have been rising at a median charge of 0.84°F per decade between 1982 and 2024—practically thrice sooner than the worldwide common of the world’s oceans. That ocean-warming pattern led Elliot Johnston, as a College of Maine PhD pupil beginning his dissertation analysis eight years in the past, to suspect there could also be impacts on what Purple Sandpipers eat in the course of the lengthy winter months.
The scientific consensus—based mostly largely on analysis from Purple Sandpiper wintering areas in Europe—has been that these birds feed primarily on mollusks, together with blue mussels, in the course of the nonbreeding season. Marine surveys within the Gulf of Maine by ecologists from the College of California, Irvine, present that regional blue mussel populations are down greater than 60% over the previous 40 years.
“Between [ocean warming] and modifications in ocean pH,” Johnston says, “mussels have declined.”
Johnston’s analysis undertaking sought to make use of DNA metabarcoding—a comparatively new methodology of analyzing what animals eat by sequencing traces of prey DNA left behind in feces—to be taught extra in regards to the wintertime weight-reduction plan of Maine’s Purple Sandpipers. To collect the required specimens for evaluation, Johnston and different graduate college students suited up in full-body orange drysuits and mittens and set out for Maine’s islands in the course of the winters of 2017–2018 and 2018–2019 to scoop up sandpiper poop. As soon as they noticed the birds, they’d look ahead to some time because the sandpipers hopped alongside the rocks.
“As they have been feeding, they have been additionally defecating,” Johnston says. When the scientists figured sufficient samples had constructed up, they’d nudge the boat in opposition to a ledge, hop out, and begin amassing. Outfitted with sampling kits that included plastic cutlery, the researchers would scoop up the tiny droppings from seaweed or rock surfaces, protect them in a buffer answer, and tuck them right into a cooler for the journey again to the college. Later, the samples have been despatched to Northern Arizona College—residence of the Pathogen and Microbiome Institute—to be analyzed. By the top of these winters, Johnston’s staff had gathered practically 200 samples.
Of the 24 prey sorts discovered by means of DNA evaluation of Purple Sandpiper droppings, barnacles dominated—showing in 88.5% of samples—whereas blue mussels, as soon as thought-about a dietary staple, have been scarcely current. Johnston says it’s nonetheless unclear whether or not the birds are switching diets as a result of warming waters have diminished mussel numbers, or whether or not the brand new methodology is solely seeing issues that older methods—comparable to abdomen content material evaluation, during which scientists visually sift by means of what a fowl has eaten—couldn’t.
Johnston provides that the decline within the Purple Sandpiper inhabitants is much from being definitively linked to their weight-reduction plan. Even when the sandpipers are switching from mussels to barnacles, that may be okay, he says.
“On the finish of the day, they want energy to maintain heat within the water and thermoregulate,” Johnston says. “In the event that they got here from barnacles, perhaps it’s not a giant deal.”
Jeff Foster, a coauthor on the research and professor within the Division of Organic Sciences at Northern Arizona College who makes a speciality of DNA metabarcoding, says he had by no means used metabarcoding to look at a shorebird’s weight-reduction plan earlier than.
“We had no thought if [this technique] would work for marine invertebrates,” Foster says, “so we thought we’d give it a shot. And it seems, it really works very well.”
Metabarcoding, Foster explains, works a bit like matching books in a library. Each species has its personal sequence, like a e-book with a singular barcode. When extracting DNA from the sandpipers’ poop, researchers search for these books and attempt to match them to a world reference library of recognized species—issues like mollusks, barnacles, or worms. Once they discover a match, they know what the fowl was consuming.
Completely different Meals, or Completely different Strategies?
As a result of the research outcomes confirmed a very completely different dominant meals for Purple Sandpipers than beforehand documented, the journal reviewers requested Foster and his staff to double- and triple-check their work.
The metabarcoding analyses, he says, “weren’t lacking the mussels, and so they have been appropriately figuring out the barnacles.”
“It’s fairly sure that they’re shifting their diets,” he provides. “It takes a variety of time, and it takes a variety of technical experience, however I actually do suppose it’s an actual shift in weight-reduction plan and never a methodological change.”
Different scientists say it’s onerous to know if the birds are actually altering their weight-reduction plan or if the brand new methodology is simply detecting prey older research missed. Gemma Clucas, a analysis affiliate on the Cornell Lab of Ornithology, makes use of related strategies to check seabird, songbird, and woodpecker diets. She says metabarcoding could be extraordinarily delicate.
“I do suppose it’s a little bit troublesome,” Clucas says, “to know whether or not what they noticed is because of a shift within the weight-reduction plan of the sandpipers, or whether or not they’re simply utilizing completely different strategies than earlier research have. … It’s probably a combination of each.”
Clucas says metabarcoding is altering how a lot scientists can find out about fowl diets. Up to now, researchers have been restricted to labor-intensive data-collection strategies, comparable to abdomen content material evaluation or spending hours watching what mother and father feed their chicks. Fecal samples, in contrast, are straightforward to gather.
“With the terns I work on, they’ll simply poop on you,” she says. “With the woodpeckers, we catch them, put them in a field, wait until they poop, after which allow them to go.”
Gathering dozens of samples shortly offers scientists a far clearer image of what birds are consuming, she says. The method has solely been broadly used for somewhat greater than a decade, however it’s already serving to researchers perceive why some fowl populations are declining.
And, Clucas says, up till now most metabarcoding research have solely centered on learning the diets of birds in the course of the breeding season. This research, she says, opens up the dialog a couple of beforehand uncared for a part of the 12 months—the nonbreeding season, which for a lot of fowl species is twice as lengthy or longer than the breeding season.
“We may undoubtedly apply [metabarcoding] extra broadly,” Clucas provides.
Brian Olsen, an ornithology professor on the College of Maine and coauthor of the research (and Johnston’s former advisor), stated that if the outcomes mirror a real shift within the Purple Sandpipers’ diets, it may assist clarify their decline in Maine and the way they may be affected by future environmental modifications. Purple Sandpipers are one in every of many species, he says, that inhabit a serious ecological boundary between subarctic and temperate zones.
“These species generally are of conservation concern as issues shift northward,” Olsen says.
What actually struck Olsen in regards to the resilient little Purple Sandpipers, he says, is how unconcerned the birds appeared whereas he was braving brutal winter situations on fowl surveys alongside the frigid Maine coast.
“You might be dwelling in a spot that will make each single human being completely depressing,” Olsen remembers fascinated with the sandpipers, “and also you’re simply as glad as might be.”
