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Congratulations to Amorina Kingdon on winning a Canadian Online Publishing Award for this article.
Thirty minutes’ drive south from the glassy condos and clogged thoroughfares of Vancouver, British Columbia, finds me near the end of a narrow dirt road flanked by farmland, where the Fraser River delta meets the sea. It’s 6:00 a.m., barely dawn on the last day of April, and alongside the road the Fraser’s south arm runs fat and sleek in its spring freshet, a bright ribbon snaking across the still-shadowy fields. I park beside the two scientists I’m accompanying for the day. We greet one another in hushed voices, close our car doors gently, fumble into hip waders. I pocket my notebooks and camera; the scientists shoulder backpacks and hoist coolers. The road ends in a grassy bank that marks the extent of all but the very highest tides; we’ve come as the tide is falling so must cross a final half kilometer of mud before reaching the actual Pacific Ocean. It will be a slog. Mudflats usually are; they’re not the most welcoming ecosystems. For humans, anyway.
We leave the road and clamber over massive tree trunks with time-softened edges, some of which are speckled with so much snow goose shit, pungent as ammonia, that the air reeks like oven cleaner. The driftwood yields to muck that sucks at our heels, then to shockingly green eelgrass swirling in pockets of seawater, and finally to bare mud that slips threateningly beneath the soles of my unfamiliar hip waders. We approach the crowd we’ve come to meet: the tens of thousands of western sandpipers that blanket the exposed mud.
They’ve set down here after flying thousands of kilometers from their winter habitat across the southern United States, Panama, and even as far south as Peru, leapfrogging along a chain of coastal mudflats that comprises the Pacific Flyway. They’ll stay for three to five days before flying north to Alaska, the last leg of their spring migration to Arctic breeding grounds. The flyway is traversed by millions of shorebirds from dozens of species each spring and fall. The sandpipers are here on layover and they have no time to waste. Today, each bird will eat up to seven times its weight in polychaete worms, arthropods, and other mudflat morsels, and will poop every two minutes.
My companions, research scientists Mark Drever and Bob Elner, start sorting their gear: cinder block–sized coolers, test tubes, paint scrapers, plastic baggies. Drever has studied various birds including ducks, woodpeckers, and seabirds for nearly 20 years, and since 2010 has focused on shorebirds with Environment and Climate Change Canada (ECCC). Elner, a scientist emeritus with ECCC, officially retired in 2008 after 17 years with the agency, but remains an active researcher. Both have spent much of their recent careers studying the western sandpiper’s grand migration, and they believe that they have uncovered one reason for the bird’s success. Today, they are gathering data to prove it—from the mud.
The birds’ backs, a mosaic of brown, black, ocher, and gold feathers, carpet the mudflat. Their snow-white bellies flash as they dart about, bobbing their heads in staccato bursts, eating so intently they ignore Elner as he sinks to one knee just three meters from the nearest bird. He slides the blade of a paint scraper along the pecked-over surface and carefully shaves off the top layer, an opalescent goo called biofilm made of marine microbes in a scum of mucus. He taps the film into a plastic test tube and snaps it closed.
While Elner scrapes, I ready my camera and squint over the birds as they gorge with an addict’s compulsion. I’m watching for something Elner observed back in the 1990s that kick-started this whole study: the birds are not just pecking invertebrate snacks, they’re also slurping biofilm off the mud.
Drever is spare with words but good-natured—imagine Ryan Reynolds’s quiet and affable older brother in khaki—and he spots me squinting at the birds. He urges me to watch how the farthest birds, about 300 meters out, are moving with the receding water’s edge. The “westerns,” as he calls them, will follow the tide gobbling tidbits until, at a certain point, they’ll turn back.
Sure enough, with no apparent trigger, most of the flock abruptly wheels to the upper flat and settles slightly above where we stand. Drever says they always turn back at the same invisible line. “We call it the Elner Break Point,” he says with a grin, explaining that the birds seem to prefer to dine higher up the shore. I sense, in this observation, how familiar the duo is with these birds and their relationship to this place.
Drever grabs a scraper and a cooler and slogs out for control samples of biofilm from where the birds aren’t eating, his silhouette receding past the Break Point. Elner gets to his feet. “I always feel euphoric out here,” he says, the freshening breeze ruffling his white hair. “I wonder if I’m getting the same high.”
His use of “high” is not hyperbolic. In the years since 2005, when he first published on the birds’ mudflat dining modes, Elner has come to theorize that the sandpipers are slurping this biofilm not only as food, but because it’s teeming with crucial fatty acids necessary to prime their bodies for migration. This “natural doping hypothesis” (as some scientists dub it), if true, draws together river, sea, mud, and birds in a synchronicity that’s playing out around us today.
When the days lengthen, phytoplankton and in particular diatoms—tiny photosynthetic organisms—in the ocean are fueled by the spring sun and explode in number. They drift in the water but also grow on the mud itself, embedded in biofilm, busily turning sunlight into food in the form of sugars. At the same time, the Fraser River’s spring freshet washes into the sea, over the delta and its diatom-studded biofilm. This freshwater shock, Elner says, “scares the shit out of them.” Like squirrels stashing nuts against the threat of winter, some of the diatom species shift their photosynthetic outputs from sugars to more energy-dense molecules: fatty acids.
In that mix of fatty acids, certain diatoms ramp up production of a variety known as omega-3 and omega-6 long-chain polyunsaturated or highly unsaturated fatty acids, and especially two called eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). While this pulse of fatty acids offers the birds energy, just as sugar does, Elner thinks the birds home in on the biofilm because EPA and DHA offer plentiful additional benefits, including priming muscles to burn fuel quicker (important for long-distance flights) and boosting immunity (handy for staying healthy while traveling under stress). And he suspects the swatch of mud above the Elner Break Point, where firmer mud is exposed longer and is easier to graze, offers birds the most fatty acids for their efforts.
Today, Elner is watching the ocean serve a timely buffet of fat, rich not only in calories but in attributes critical to the birds’ ultra-athletic migratory feat, on an easy-to-access muddy platter. The word “dope” might suggest an optional performance booster, but to him, the fatty acids are nonnegotiable—the birds need them to make their trip on time and in good health.
To prove that this surge of fresh water sets up this fat-making bonanza, Elner and Drever have come out to the mudflats with their scrapers all spring to measure biofilm fatty acids, particularly EPA and DHA. Elner and Drever are looking for a pulse of fatty acids that correlates with the water’s shifting salinity. It’s one piece of a larger hypothesis: that shorebirds, as long-distance migrants, have exceptional physiological demands; that fatty acids plentiful in the sea have a unique ability to support these needs; that diatoms on marine mudflats produce these fatty acids; and that the birds deliberately target foods like biofilm that contain them.
If they can demonstrate this relationship here on Roberts Bank, it could be a boon for the conservation of migratory shorebirds, which travel and feed along the world’s coastlines. Tidal flats, including mudflats, have declined starkly around the world in recent decades thanks to human activity. Shorebird populations have plummeted, too. Scientists have assumed the birds are suffering from habitat or calorie loss. They certainly are. But what if they can also be affected by changes to the fatty acids on those precious mudflats? If Elner is correct, this new dimension of the bird-mud relationship could give conservationists a new focus for solutions, annoy developers with new constraints, and describe a spectacular interdependence between marine and terrestrial life that shorebirds embody around the world.
Fatty acids are a fantastic candidate for dope upon which a long-distance migrant might depend. These simple chains of carbon atoms come in all shapes and sizes—as short as five carbons or as long as 22, kinked or straight, fragile or robust. Their many physical forms translate into different properties, and that lets them fill an impressive roster of roles in an animal’s body. And the EPA and DHA Elner is interested in? They are some of the most versatile and impressive of all.
Everyone I ask about the details of what fatty acids actually do for migratory birds points me to Chris Guglielmo, a biologist at Western University in Ontario, who believes that the definitive way to see if the birds really are benefitting from fatty acids is to do testing in the wild, but the next best thing is to use an atmospheric treadmill. Fortunately, he codirects the Advanced Facility for Avian Research and has access to a large wind tunnel. With the cross section of a squashed octagon one meter tall, two meters long, and one and a half meters wide, the wind tunnel can hold a bird for hours flying at about 40 kilometers per hour, letting Guglielmo mimic its migration—and the physiological effects.
Guglielmo did his PhD on western sandpipers at Simon Fraser University in British Columbia from 1994 to 1999. He worked with Elner, and they discussed the biofilm work, but Guglielmo graduated before the findings on biofilm’s significance emerged. When we first chatted about his work in 2018, he was still on the fence about the doping theory. “That’s my job as a scientist,” he said to me then, “to be skeptical.”
Guglielmo is rigorously logical; he wastes little breath on unsupported ideas. To be clear: he’s not saying that doping doesn’t happen. He just doesn’t think the necessary experiments to prove it have been done. Proving the westerns are eating long-chain fatty acids in situ is good, but the hypothesis requires confirming that the birds are actually faster, stronger, and healthier afterward. He says it’s entirely reasonable to think they would be.
For one, Guglielmo explains, these fatty acids are one of the “master controllers” of the genes that can stimulate an animal’s metabolism to burn more fat, and fat is a spectacular energy source: it has about nine calories per gram, while carbohydrates or protein yield closer to four.
In addition, long-chain fatty acids may speed up the rate of muscle metabolism by physically changing muscle cell membranes and making them more fluid. Every cell membrane is made of fatty acids, which help control how fast fuel can move in to power the cell. Shorter and straighter fatty acids are more solid, while longer, kinkier fatty acids are more fluid. EPA and DHA are the longest and kinkiest of all.
Fatty acids can also boost immune function by helping make hormones—keeping the birds healthy on their global travels.
A ready-to-eat molecule that speeds up metabolism, mobilizes fat for burning, and fights illness during an ultramarathon? Seems legit. But Guglielmo has reasons for his skepticism, largely because of his work with the yellow-rumped warbler.
It belongs to a group of songbirds that also migrates huge distances across North America. The blackpoll warbler, for example, puts in stints up to 70 hours, far longer than the average western sandpiper flight. Surely if any animal needs doping, warblers do. In 2014, Morag Dick, Guglielmo’s graduate student at the time, fed some yellow-rumped warblers diets enriched with various levels of DHA, while others had an unenriched diet. Then she flew them in the tunnel for up to six hours. Even though their muscles showed some biochemical changes, warblers fed the fatty acid–rich diet didn’t seem to get a performance boost compared with those fed the unenriched diet. “We couldn’t find any benefit in warblers,” Guglielmo says.
“My perspective was that, well, if [long-chain polyunsaturated fatty acids] are good for exercise, they should be good for exercise in all birds,” he says. Doping isn’t much of a theory if it isn’t applicable outside of one species on one mudflat.
But Guglielmo didn’t dismiss the doping hypothesis outright, because there is actually a curious and fairly good reason why sandpipers might be “doping” when the warblers don’t. Yellow-rumped warblers are songbirds adapted to eat from a terrestrial food web, whereas sandpipers are shorebirds and, at least during their migrations, eat food from the ocean—they are basically marine birds. And there’s a profound dichotomy between marine and terrestrial ecosystems in how animals get access to those long-chain unsaturated fatty acids.
Cornelia Twining, an ecologist now at the Swiss Federal Institute of Aquatic Science and Technology, described this dichotomy in a 2015 paper that synthesized what was known about the amount and nutritional value of EPA and DHA in food webs around the world, from land and sea, from the poles to the tropics. Chief among her observations was that there are more of these primo fatty acids in water—lakes, streams, and oceans—than on land.
Every animal, on land or in water, needs a small amount of these fatty acids. Unrelated to any possible performance benefit in migrant shorebirds, they help build organs such as brains and eyes, and they support immune function. But almost no animals can make their own EPA and DHA—they must eat them. It’s a bit like how every animal needs carbohydrates as fuel and must consume something to get them. That’s how food chains work: producers at the bottom, consumers farther up. But while terrestrial and aquatic primary producers alike can make carbohydrates—trees on land and phytoplankton in the water, for example—the only organisms, as far as we know, that actually build EPA and DHA from scratch are aquatic. These synthesis pros are largely phytoplankton, but new studies are showing that some invertebrate species can also build fatty acids de novo. As a result, aquatic ecosystems generally have more of these fatty acids, while terrestrial ecosystems have far fewer.
Twining says scientists are not certain why fatty acids are made more abundantly in water, but she speculates that it might have something to do with their fragility. “[Long-chain fatty acids are] very sensitive to being broken down by oxygen, or things like light or high temperatures,” she says, “so in aquatic systems they’re more buffered.” Whatever the reason, most aquatic food webs, with their base of fatty acid–producing phytoplankton, have relatively high levels of these fats.
How, then, do terrestrial animals get their fatty acids? Many have a workaround. Twining says many terrestrial organisms actually do synthesize these fatty acids—but not from scratch. Instead, they build onto and reconfigure slightly shorter fatty acids they get through their diet: sort of like tricking out a cheaper car if you can’t get an expensive one. Luckily, these precursors are plentiful on land in the leaves, nuts, and seeds of terrestrial plants.
However, this synthesis costs an animal energy and is less efficient than just eating the EPA and DHA directly. So, if an animal’s diet is rooted in an aquatic or marine food web, it’s probably getting plenty of the “good stuff” ready-made through the foods it eats and likely hasn’t evolved to be very efficient at this synthesis. It doesn’t need to be. “Why bother doing extra work, basically?” Twining says.
And that is why sandpipers and other shorebirds might need to “dope.” Sandpipers are terrestrial—but they migrate along marine coasts. Could they, in theory, have come to rely on the ocean’s plentiful, ready-made dietary fatty acids at this critical time, instead of spending precious energy synthesizing them? That might also explain why Guglielmo’s warblers performed no better with a dietary boost from fatty acids: as terrestrial birds, they’ve had to get pretty good at making their own.
Like Guglielmo, Twining believes “the jury is still out” on the natural doping hypothesis. She says that getting long-chain fatty acids through diet rather than synthesis would be greatly beneficial to shorebirds, but the science on whether fatty acids actually bestow further benefits to migrating shorebirds—and, if so, which particular fatty acids or mix thereof—remains unclear.
But some intriguing studies on semipalmated sandpipers, suggesting that they too target biofilm, hint that on another coast, on another flyway, another migrant shorebird might offer more clues.
The sea between Nova Scotia and New Brunswick rises and falls up to 16 meters every day. The Bay of Fundy has the highest tides in the world, and through the shimmering August air, at the tide’s lowest ebb, I can’t see the ocean from the shore. Instead, kilometers of russet mud stretch before me, crisscrossed by massive ditch-like runnels.
I’m here to see semipalmated sandpipers winging south. These close cousins of the western sandpipers summer in the Arctic and subarctic, but now they’re heading to Central and South America. This population is hopping from mudflat to mudflat down the Atlantic flyway—and there is a lot of mudflat in Fundy.
I begin my walk onto the flat in zip-up neoprene scuba booties, but eventually give up and just plunge my bare feet into the mud, which turns out to be exactly as fun as you might think. If Roberts Bank was a pillowtop mattress, this is a softer, heavily iced, three-layer cake.
I have it easy compared with Matt Mogle, who is battling the same mud while pulling a two-meter-long blue plastic sledge laden with scientific equipment, like an Antarctic explorer trudging poleward, with his buzz cut and fieldwork tan.
A grin breaks over Mogle’s face every time we traverse one of the runnels without skidding back to the bottom. Mogle is a master’s student at Mount Allison University in Sackville, New Brunswick. His lab studies shorebird ecology, and he’s focusing on biofilm and its nutrients, including lipids of which fatty acids are a subset. Sackville is tucked in one of the two upper arms of the Bay of Fundy, where the tides are highest and the mud is thickest, attracting millions of shorebirds every year. Fifty to 95 percent of the world’s semipalmated sandpipers—“semis”—will pass through the various mudflats of the upper bay each fall.
They’re here now, en masse at Peck’s Cove, one of Mogle’s study sites. I excitedly ask him if the birds are gorging on biofilm. “It does seem to be making a significant contribution,” he says, a slight Midwestern twang revealing his Kansan roots. But while they do graze it, Mogle continues, biofilm may not be the semis’ biggest priority here. They’re focusing on something else.
We squelch to a stop and Mogle swipes a finger through the mud. A translucent shrimplike animal about the length of an eyelash squirms on his fingertip. He gestures to the mud around us. “It sounds like Rice Krispies,” he says, grinning. Sure enough, that breakfast-cereal sound whispers all around: Snap. Crackle. Pop.
I crouch and immediately regret it. The gray-brown mud is honeycombed with millions of tiny holes, each crawling with a tiny white body. I’ve been tromping on these little amphipods called Corophium—colloquially, mud shrimp—without noticing. I lift one foot: several are squirming on my skin.
So if Corophium is the meal of choice for the shorebirds on this mudflat, what about biofilm? Mogle tells me that Fundy’s biofilm blooms in volume twice a year: in spring, and then around now, in August and September. The Corophium also breeds biannually, first in the spring, and then later in the summer. “It seems like they’re kinda tied together,” he says. “When the biofilm blooms, and when the Corophium reproduces.”
I look around with this new knowledge. The birds may not be gorging on biofilm with the same intensity as on Roberts Bank, but the biofilm still underpins the food web. The mud shrimp are eating the biofilm, and the birds are eating the mud shrimp. As on Roberts Bank, migrating shorebirds are getting fatty acids from the biofilm, but in this case, they’re one species removed.
Mogle’s biofilm collection method is fancier than Elner’s. He sets a small metal cap the diameter of a Snapple lid on the mud, cup down. Then he opens a canister from the sledge to reveal liquid nitrogen. Having recently had a wart burned off, I wince as he pours the evilly hissing liquid over the cap. Steam wheels off into the air and droplets dance across the metal.
When the last droplets have dissipated, Mogle lifts the chilled cap with its puck of flash-frozen biofilm. He’ll quantify the biofilm, its productivity, and its proportions of carbohydrates, protein, and fat, which will shed light on what goes into the mudflat food web.
Mogle says he has always been drawn to unknowns, and biofilm is a black box here, especially how the birds use it. “We’re just starting to collect data on which of the mudflats [within the Bay of Fundy] they slurp it off,” he says, adding that they want to see what the birds can get from the Bay of Fundy that they can’t get elsewhere.
As I go through my notes that evening, I feel excited at the pattern I sense: shorebirds slurping biofilm on the west coast, shorebirds eating biofilm (via Corophium) on the east coast. But my excitement at the prospect of a simple correlation is complicated the next day by Diana Hamilton, one of Mogle’s advisers and the leader of the Mount Allison shorebird lab, as we talk over tea in her office.
“I don’t know if anyone told you,” she says, “but Corophium are introduced.”
Hamilton explains that the mud shrimp were stowaways on wooden ships during the age of sail, a European species that hitchhiked across the water and found a new home. The birds have only been eating Corophium for a few centuries. They’re a great food source, she says, but the details of the birds’ diet before the mud shrimp entered the flats remain a mystery.
Hamilton is tall with curly brown hair and the calm, resigned air of a veteran in the midst of the field season bustle. She did her first semipalmated sandpiper tracking study at Mount Allison University in 2005, and in 2006 observed the birds “skimming” as they fed on a Fundy mudflat, a slurp-like behavior that she and her team linked to the birds preying on ostracods—a type of crustacean. She began looking into the literature on feeding behaviors. She had previously considered biofilm only as the base of the mudflat food web, but then she encountered research, including Elner’s paper that described birds grazing biofilm on Roberts Bank. “That got me thinking,” she says, “what are they doing here?” When she looked closer, she spotted the Fundy semipalmated sandpipers eating biofilm directly and began studying biofilm as an actual food source. Now, Mogle is looking deeper.
I ask if the semis need to eat biofilm for its fatty acids here, the way Elner and Drever think they need it on Roberts Bank. Hamilton isn’t sure: biofilm is definitely on the menu. But semis target a variety of prey at a handful of different mudflats in upper Fundy—polychaete worms, Corophium, and other invertebrates in addition to biofilm. However, as Hamilton knows from her studies of mudflat food webs, biofilm underlies everything, supporting not just the Corophium at Peck’s Cove, but all the birds’ prey. So the birds are getting fatty acids both directly from biofilm and indirectly from prey that eat the biofilm.
Another mudflat, another food web to untangle. It’s no wonder the relationship between birds, biofilm, and fatty acids is so tricky. Hamilton is a meticulous scientist, cautious of absolute statements, yet she says the birds certainly need fatty acids, even if the details of how, or why, are knotty. And she is absolutely confident of the importance of coastal mudflats: “They are 100 percent critical for birds in this region.”
Tidal flats are dynamic structures, balanced between replenishing land and eroding sea. They form where sediment worn off the land spills into the ocean. This is often at the mouth of a large river, where the density of human activity can affect these processes.
Dams trap sediment upstream before it reaches the flat. Loss of vegetation quickens erosion. Docks, piers, and walls stop sediment accumulation. Accelerating coastal development and other human activities like dam building are major reasons why the world has lost 16 percent of its tidal flats in the past three decades.
In the same time, shorebirds have been in steep decline. Globally, 45 percent of Arctic-bound migratory species are dwindling. North America has lost about one-third of its shorebirds.
On the East Asian-Australasian Flyway, which spans the hemispheres from Siberia to Australia, shorebird numbers have been declining at some stopovers by up to eight percent a year as developments harden the shore.
Understanding and measuring the relationship between shorebirds and fatty acids amid the more obvious stress of lost habitat—across a chain of mudflats—is ridiculously difficult. But if Elner and Drever do manage to validate their hypothesis, it could help at least some struggling birds by highlighting a new conservation target that’s been overlooked until now. After all, a mudflat can remain intact—even apparently food-rich—but human activity can still impact its fatty acid production, as demonstrated on Roberts Bank.
In 2013, the Vancouver Fraser Port Authority (VFPA) started the environmental review for the Roberts Bank Terminal 2 (RBT2) project, which would approximately double the size of an already sprawling container ship terminal at Roberts Bank. A 2015 environmental assessment prepared by the port found that RBT2 would pool fresh water from the Fraser River behind the new artificial island—on the very mudflat where the western sandpipers graze their biofilm. ECCC scientists, Drever and Elner included, raised concerns. The Terminal 2 structure basically captures river water and ponds it on the tidal flat, Elner says. That’s a problem, because diatoms will react to changes in salinity—that’s why the river’s seasonal freshet shocks them into producing fatty acids in the first place. If there is fresher water year-round, it would blunt the spring salinity shock, so diatoms might not get cued to produce fatty acids. Additionally, if the diatom species present in the biofilm shifted toward those that are used to fresher water, such species are even less likely to get shocked into producing fats.
However, the doping hypothesis hasn’t figured in the VFPA’s environmental assessment, because they used a common ecosystem model that tallied organisms solely in terms of biomass, comparing the amount of fish, invertebrates, and algae before and after the new docks. Nutrient value wasn’t calculated; only calories were. If biomass was the same after construction, by their math, it would mean that the impact was negligible.
When it came to biofilm, the VFPA’s model found that the salinity changes triggered by construction would indeed alter the diatom species present, but there would be the same or even a slightly greater amount of biofilm on the mudflat post-construction: ergo, the birds would be fine.
Elner says this misses the point. If the biofilm doesn’t make the fatty acid pulse, then the birds aren’t getting primed.
His and Drever’s work hasn’t changed the VFPA’s mind so far. In March 2020, an expert panel set up to review RBT2 issued their report, which stated, “Due to the recent and still-emerging scientific understanding of biofilm, the panel is unable to conclude with reasonable confidence that the project would or would not have a residual adverse effect on western sandpiper.” The port continues to study biofilm broadly, focusing on creation and restoration rather than preservation. The panel recommended the port increase knowledge of biofilm and specifically of its fatty acid production; the port says it will work to implement these recommendations, “should they be made into conditions” of the project.
The science may be still emerging, but evidence is mounting rapidly. Drever and Elner’s first peer-reviewed paper linking the spring freshet, salinity, and fatty acids with the western sandpipers during 2016 came out in August 2019. The primo fat concentration in the biofilm peaked that year on May 11, just as the Fraser River brought salinity to its lowest, supporting salinity as the fatty acid pulse’s trigger. Another step forward for the theory. Three more papers have followed since, using data gathered since 1999. The April 2019 morning I spent with the researchers will inform still more papers.
Drever and Guglielmo planned to fly western sandpipers in the wind tunnel in the summer of 2020, but the pandemic thwarted their plans. They hope to try again in 2021, favorable vaccination rates and case counts willing.
But other work has continued, including one study that hints shorebirds may indeed respond differently than warblers to fatty acid “dope.” One of Guglielmo’s students, for instance, cultured muscle cells from sanderlings (a shorebird) and yellow-rumped warblers (a songbird) and doused them with long-chain fatty acids. The sanderling cells seemed to respond differently from the warbler cells, and from a control culture of mouse cells, by increasing their aerobic capacity. “It did kind of make me more open to the idea that shorebirds are more triggered by [polyunsaturated fatty acids],” Guglielmo says.
To prepare for the wind tunnel work, the lab has tweaked the diet of some captive western sandpipers, adjusting it to a mix similar in fatty acids to that of biofilm. Now, before tunnel flights, the lab can more realistically dope the birds.
“The next step,” Guglielmo says, “is to put the whole story together and answer the question.”
Mogle’s work continues, too. He obtained some biofilm samples from Roberts Bank in the summer of 2020 and aims to get further samples collected in 2021. He’s analyzed the 2020 samples by the same metrics—productivity, macronutrient breakdown—as in Fundy, and preliminary numbers show that the biofilm on the western sandpiper’s preferred feeding swatch, above the Elner Break Point, appears to be richer in protein, carbs, and, yes, lipids, than another nearby mudflat.
At one point, as I’m standing with Elner on the mudflat in April, he says, “I want to see what the birds are telling us.”
I do, too. I know things are rarely as simple as we would like them to be, but I sense a pattern around me, in the tableau of that April morning and the studies I’ve read since then. Semipalmated sandpipers breeze through Fundy when Corophium is breeding and gobbling fatty biofilm. Tree swallow chicks survive better when they eat fatty acid–rich aquatic insects emerging from lakes and streams. Red knots arrive in Delaware Bay every spring to a glut of marine fat in the form of horseshoe crab eggs. Even fish may demonstrate this pattern: stickleback species moving from marine environments into fresh water increase their ability to make their own fatty acids. And western sandpipers alight on Roberts Bank just as the river shocks the diatoms to pulse with fatty acids, flocks wheeling and swirling back to the fat year after year after year, slurping off the mud as though their lives depended on it.