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A Naturalist’s View of “Extraordinary” North Carolina

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On April 17, 2023

In Animals, Art, Biology, Climate/Global Change, Environment/Sustainability, Lecture, Science Communication & Education

Naturalist Tom Earnhardt on Black River in North Carolina. The forests around Black River are home to the oldest trees in eastern North America, 2,700-year-old bald cypresses.
All photos courtesy of Tom Earnhardt.

There are many ways to think of North Carolina. It was the 12th U.S. state to enter the Union. It is bordered by Virginia, Tennessee, Georgia, and South Carolina. North Carolina’s capital city is Raleigh, and it has an estimated population of 10,698,973. These are all facts, but they tell only part of the story: the human side of it.

Naturalist Tom Earnhardt offers other ways to view North Carolina: the state contains the oldest forest in the eastern United States, with trees up to 2,700 years old. It has 17 river basins, and some of its rivers show evidence of fishing weirs used by indigenous tribes hundreds of years ago. And from the Atlantic coast in the east to the Appalachian mountains in the west, North Carolina is home to thousands of native plants, animals, and fungi. There are 3,000 species of moths alone in North Carolina, and “Every one is essential; not one is optional.”

“North Carolina,” Earnhardt says, “is still one of the most biodiverse and extraordinary places on the planet.”

A prothonotary warbler. Prothonotary warblers inhabit swamps and coastal rivers in North Carolina. They are one of only two warblers in America that nest in cavities.

Earnhardt is a naturalist, photographer, writer, and attorney. He wrote and produced the show “Exploring North Carolina,” a series of dozens of episodes about North Carolina’s biodiversity, geography, and history. Earnhardt recently visited Duke to speak at the Nasher Museum of Art.

One inspiration for his talk was the ongoing Nasher exhibit “Spirit in the Land,” an exploration of ecology, culture, and connection to the natural world. “Art in its many forms,” Earnhardt says, “tells a story of love, loss, and renewal.”

Black River in North Carolina.

Earnhardt has spent much of his career balancing caution and hope. We are facing environmental crises, including climate change and biodiversity loss. Earnhardt believes it’s important for people to know that, but he has put a lot of thought into how to get that message across. Earnhardt has learned that it can help to “tell it as though it was your best friend or brother who needed to hear an important story.” Science alone isn’t always enough. “To hear bad news of any kind is not easy,” Earnhardt says, “and people want to hear it from people they know, people they trust or can relate to.”

The stories he tells aren’t always easy to hear, but they are important. We need to know — whether on a local, state, national, or international scale — what exactly we stand to lose if we continue on a path of environmental destruction. Many species are becoming more scarce, Earnhardt says, “but we still have them.” They can’t be protected once they’re gone, but many of them are still here and can still be preserved. The goal for all of us should be to keep it that way.

North Carolina, Earnhardt says, is at “the epicenter of the temperate world.” The state has a range of climates and habitats. It marks the northernmost native range of the American alligator, while coniferous forests in the North Carolina mountains resemble boreal forests of the northern U.S. and Canada. North Carolina, according to Earnhardt, contains “whole ecosystems that other states only dream about.”

Eastern North Carolina is characterized by beaches, salt marshes, and other coastal ecosystems. Here you can find “wildflowers that grow in salty sand” and painted buntings, multicolored songbirds unlike any other in North America. On four occasions, he’s even seen manatees in North Carolina.

A male painted bunting, a summer resident on North Carolina’s barrier islands. Female painted buntings are bright green.

“Travelers from around the world vacation here and raise their families in the summer,” Earnhardt says—and he’s not talking about humans. Many shorebirds and sea turtles lay their eggs on North Carolina’s beaches. Human disturbance, including artificial lighting and crowded beaches, can put their babies in danger. Minimizing light pollution near beaches, especially during turtle nesting season, and staying away from nesting shorebirds can help.

A longleaf pine savanna in southeastern North Carolina.

Moving farther west, we can find savannas of grasses and pine trees. “You drive past this, and people go, ‘ho hum, a pine barren.’” To that Earnhardt says, “Look a little closer.”

White-fringed orchids, one of North Carolina’s 80 native orchid species. Earnhardt took this photo in the Green Swamp, a longleaf pine savanna nature preserve.

These pine barrens are home to some of North Carolina’s 80 species of orchid, like the white-fringed and yellow-fringed orchids. “Look at them from all angles,” Earnhardt urges, “because from up above it becomes a sunburst… for those who watch.”

A yellow-fringed orchid, viewed from the side.

Be one of those who watches.

A yellow-fringed orchid, viewed from above.

North Carolina rivers, forests, and swamps are also home to many wildlife species. Forests around Black River contain “huge buttresses of tupelo that hold the world together” and bald cypresses that have been alive for 2,700 years. The early years of these now-ancient cypress trees coincided with the fall of the Assyrian Empire and the establishment of the first emperor of Japan. Many centuries later, they are the oldest trees in eastern North America.

Cypress trees on Black River. Both tupelos and cypresses have buttresses at their bases to provide stability in the water.

They are also in danger. “If seas rise three feet,” Earnhardt says, “there will be enough pressure to flood these [trees]…. We could lose them.” But “they are worth saving.”

Still farther west are the Appalachian mountains, another biodiversity hotspot. North Carolina is home to 60 species of salamanders, many of which live in the mountains. The southern Appalachians and western North Carolina contain more salamander diversity than anywhere else on the planet. One species that lives here is the American hellbender, a two-foot-long denizen of mountainous streams.

Despite increasing human development, North Carolina is still rich in flora and fauna. “We have wild places,” Earnhardt says. North Carolina has more than 450 bird species, over 30 native pitcher plants, 20 freshwater turtles, and 38 snakes—“and they’re all good neighbors,” Earnhardt adds.

Venus flytraps in a longleaf pine savanna.

North Carolina has pink and yellow lady slippers and ten-foot-tall Turk’s Cap lilies; crayfish and thousands of mushrooms; native azaleas and insects that depend on them. It has Earnhardt’s “new favorite bird,” the swallow-tailed kite, and vultures, “the clean-up crew: not optional.” That’s a refrain throughout Earnhardt’s talk. “Nothing I’ve shown you tonight is optional,” he says.

“Both in banking and nature,” Earnhardt says, “when we make too many withdrawals and not enough deposits… there’s a deficit.” There are too many creatures we have already lost. The eastern cougar. The Carolina parakeet. The passenger pigeon. Too many more. There are still others that are threatened or endangered but not yet gone. “We humans tend to forget the failures and close calls,” Earnhardt says. While talking about biodiversity loss, he references a quote by biologist E.O. Wilson: “This is the folly our descendants are least likely to forgive us.”

A swallow-tailed kite. Earnhardt says that these kites, which spend their winters in South America, now nest along several rivers in southeastern North Carolina.

So what can be done? To preserve biodiversity, we have to consider entire ecosystems, not just one endangered animal at a time. “We are part of the natural world, part of links and chains and pyramids,” Earnhardt says, and humans too often forget that. Everything is connected.

He recalls visiting entomologist Bill Reynolds’s lab and noticing crickets hopping across the floor. “Don’t step on the transmission fluid!” Reynolds warned. He was referring to the crickets and to insects more broadly. Like transmission fluid in cars, insects are essential to making sure the systems they are part of run smoothly. Insects serve crucial roles in food webs, pollination, and decomposition. Studies show that they are declining at alarming rates.

“We are at a crossroads,” Earnhardt says. “Our transmission fluid is low, and we have made too many withdrawals from the bank of biodiversity.” Still, he emphasizes the importance of not giving up on wildlife conservation. Given a chance, nature can and will regenerate.

Tupelo tree buttresses on Tar River near Greenville, North Carolina.

Despite all our past and current failures, conservation also has remarkable success stories. The brown pelican is one North Carolina resident that almost went extinct but has since “come back in incredible numbers.” The bald eagle is another. Its population plummeted in the 20th century, largely due to the insecticide DDT as well as habitat loss and hunting. By 2007, though, after intensive conservation efforts, it had rebounded enough to be removed from the endangered species list. Until about 1980, Earnhardt had never seen a bald eagle in North Carolina. Today, Earnhardt says, “I see them in every county.”

A bald eagle that Earnhardt saw near the Raleigh-Durham airport. Bald eagles, once on the brink of extinction, can now be seen in every county in North Carolina.

“Everyone’s going to have to fly in the same direction,” to preserve North Carolina — not to mention the rest of the world — at its best and wildest, Earnhardt says. But individual actions can make a difference. He suggests planting native flowers like milkweed and coneflower, both of which are good food sources for pollinators. And if you choose to plant ornamentals like crepe myrtle, “Treat that as a piece of art in the yard and then plant the rest as native.”

Lady Bird Johnson, a former first lady and conservation advocate, once said that “Texas should look like Texas, and Mississippi like Mississippi.” Choosing native plants can be a powerful way to help native wildlife in your own yard. “If you plant it,” Earnhardt says, “they will come.”

One audience member asks, “How do you recommend that we recruit non-believers?” It’s a conundrum that Earnhardt has put a lot of thought into. “It takes time, and it takes patience,” he says. “Some of my best friends are not full believers, but I work on them every day.”

Post by Sophie Cox, Class of 2025

The Brain Science of Tiny Birds With Amazing Memories

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On March 24, 2023

In Animals, Behavior/Psychology, Biology, Computers/Technology, Data, Lecture, Neuroscience

A black-capped chickadee. Dmitriy Aronov, Ph.D., brought wild black-capped chickadees into the lab to study their memories.
“Black-Capped Chickadee” by USFWS Mountain Prairie is licensed under CC BY 2.0.

Black-capped chickadees have an incredible ability to remember where they’ve cached food in their environments. They are also small, fast, and able to fly.

So how exactly can a neuroscientist interested in their memories conduct studies on their brains? Dmitriy Aronov, Ph.D., a neuroscientist at the Zuckerman Mind Brain Behavior Institute at Columbia University, visited Duke recently to talk about chickadee memory and the practicalities of studying wild birds in a lab.

Black-capped chickadees, like many other bird species, often store food in hiding places like tree crevices. This behavior is called caching, and the ability to hide food in dozens of places and then relocate it later represents an impressive feat of memory. “The bird doesn’t get to experience this event happening over and over again,” Aronov says. It must instantly form a memory while caching the food, a process that relies on episodic memory. Episodic memory involves recalling specific experiences from the past, and black-capped chickadees are “champions of episodic memory.”

They have to remember not just the location of cached food but also other features of each hiding place, and they often have only moments to memorize all that information before moving on. According to Aronov, individual birds are known to cache up to 5,000 food items per day! But how do they do it?

Chickadees, like humans, rely on the brain’s hippocampus to form episodic memories, and the hippocampus is considerably bigger in food-caching birds than in birds of similar size that aren’t known to cache food. Aronov and his team wanted to investigate how neural activity represents the formation and retrieval of episodic memories in black-capped chickadees.

Step one: find a creative way to study food-caching in a laboratory setting. Marissa Applegate, a graduate student in Aronov’s lab, helped design a caching arena “optimized for chickadee ergonomics,” Aronov says. The arenas included crevices covered by opaque flaps that the chickadees could open with their toes or beaks and cache food in. The chickadees didn’t need any special training to cache food in the arena, Aronov says. They naturally explore crevices and cache surplus food inside.

Once a flap closed over a piece of cached food (sunflower seeds), the bird could no longer see inside—but the floor of each crevice was transparent, and a camera aimed at the arena from below allowed scientists to see exactly where birds were caching seeds. Meanwhile, a microdrive attached to the birds’ tiny heads and connected to a cable enabled live monitoring of their brain activity, down to the scale of individual neurons.

An artistic rendering of one of the cache sites in an arena. “Arenas in my lab have between 64 and 128 of these sites,” Aronov says.
Drawing by Julia Kuhl.

Through a series of experiments, Aronov and his team discovered that “the act of caching has a profound effect on hippocampal activity,” with some neurons becoming more active during caching and others being suppressed. About 35% percent of neurons that are active during caching are consistently either enhanced or suppressed during caching—regardless of which site a bird is visiting. But the remaining 65% of variance is site-specific: “every cache is represented by a unique pattern of this excess activity in the hippocampus,” a pattern that holds true even when two sites are just five centimeters apart—close enough for a bird to reach from one to another.

Chickadees could hide food in any of the sites for retrieval at a future time. The delay period between the caching phase (when chickadees could store surplus food in the cache sites) and the retrieval phase (when chickadees were placed back in the arena and allowed to retrieve food they had cached earlier) ranged from a few minutes to an hour. When a bird returned to a cache to retrieve food, the same barcode-like pattern of neural activity reappeared in its brain. That pattern “represents a particular experience in a bird’s life” that is then “reactivated” at a later time.

Aronov said that in addition to caching and retrieving food, birds often “check” caching sites, both before and after storing food in them. Of course, as soon as a bird opens one of the flaps, it can see whether or not there’s food inside. Therefore, measuring a bird’s brain activity after it has lifted a flap makes it impossible to tell whether any changes in brain activity when it checks a site are due to memory or just vision. So the researchers looked specifically at neural activity when the bird first touched a flap—before it had time to open it and see what was inside. That brain activity, as it turns out, starts changing hundreds of milliseconds before the bird can actually see the food, a finding that provides strong evidence for memory.

What about when the chickadees checked empty caches? Were they making a memory error, or were they intentionally checking an empty site—even knowing it was empty—for their own mysterious reasons? On a trial-by-trial basis, it’s impossible to know, but “statistically, we have to invoke memory in order to explain their behavior,” he said.

A single moment of caching, Aronov says, is enough to create a new, lasting, and site-specific pattern. The implications of that are amazing. Chickadees can store thousands of moments across thousands of locations and then retrieve those memories at will whenever they need extra food.

It’s still unclear how the retrieval process works. From Aronov’s study, we know that chickadees can reactivate site-specific brain activity patterns when they see one of their caches (even when they haven’t yet seen what’s inside). But let’s say a chickadee has stored a seed in the bark of a particular tree. Does it need to see that tree in order to remember its cache site there? Or can it be going about its business on the other side of the forest, suddenly decide that it’s hungry for a seed, and then visualize the location of its nearest cache without actually being there? Scientists aren’t sure.

Post by Sophie Cox, Class of 2025

Spongy Moss, Living Jelly, and Other Early Spring Delights

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On March 9, 2023

In Animals, Biology, Science Communication & Education, Students

Duke biology professor Paul Manos, Ph.D., looking at peat moss with Wild Ones members Gurnoor and Dhruv.

The Wild Ones club recently visited the Duke Forest with biology professor Paul Manos, Ph.D., and herpetology professor Ron Grunwald, Ph.D., to look for salamander eggs and other early spring delights.

It was warm and sunny, and wildflowers sprouted up alongside the trail, but most of the trees were still bare. “It’s kind of nice to look in a forest without any leaves,” says Manos. “They get in the way a lot.” We examined winged elm and shagbark hickory at the trailhead, then windflower and bluets right beside the path. Many early spring wildflowers take advantage of the higher levels of sunlight that reach the forest floor before trees develop leaves.

A shagbark hickory tree in the Duke Forest. “Shagbark” refers to the peeling strips on the trunk. The word “hickory,” meanwhile, comes from an Algonquin word for both the tree and a food made from pounded hickory nuts.

Manos was delighted to find a patch of sphagnum moss beside the trail. He says sphagnum, also known as peat moss, is usually found in higher latitudes, like the United Kingdom and Canada, where it grows in huge fields known as moorlands or quaking bogs.

When we reached a small pond, Grunwald swept a long-handled net through the water and leaf litter and pulled out a gelatinous glob that promptly became a highlight of my week/month/year: spotted salamander eggs. I don’t know what the rest of you spent your childhoods doing, but I spent a good portion of mine looking for frog eggs (and sometimes finding them) and wanting to find salamander eggs (and never finding them). But here they were, in front of me, tinted green with algae and glinting in the sunlight and close enough to touch.

Bluets are members of the coffee family, which Manos says is “known for having a lot of chemical diversity.” Many of the members of that family grow in the tropics, but some, like this bluet, live in more temperate regions.

This strikes me as an appropriate retort to many unrelated things. Calculus test? Yeah, okay, but I saw salamander eggs. The grosbeaks that Wild Ones went looking for two weeks ago are still thwarting me? Yes, and I still haven’t gotten over it. However: salamander eggs.

Sphagnum moss. It is wonderfully moist and spongy.
Photo by Lydia Cox, one of the student leaders of Wild Ones.

The egg mass was less firm and less slimy than I expected. It felt remarkably similar to jelly. “This gel,” Manos says, “apparently doesn’t allow oxygen to move through it very well,” but the developing spotted salamander larvae need oxygen. The solution is ingenious: a partnership with green algae. A species of algae grows on the egg masses and penetrates individual eggs, and eggs with more algae grow and develop faster.

The algae are photosynthetic, creating carbon and oxygen products from carbon dioxide gas and sunlight. That process likely provides supplemental oxygen to the salamander embryos, and one study found that the salamanders also absorb carbon produced by the algae’s photosynthesis.

Herpetology professor Ron Grunwald with spotted salamander eggs.

That carbon fixation is the first known example of carbon transfer from algae to a vertebrate host, though similar partnerships have been found in invertebrates, and the authors of the study speculate that similar processes may be occurring in other amphibians as well.

The particular species of algae that grows on spotted salamander eggs is in the Oophila, which according to Manos means “egg lover.” The partnership, however, is temporary. “It’s a very short-lived, ephemeral story,” Manos says.

“This is the best day of my life,” says Michelle, a Wild Ones member, while holding spotted salamander eggs. Comments from other students included “This feels weird,” “That is a sublime experience,” and “Nature’s fidget.”

In addition to the spotted salamander eggs, Grunwald also found a marbled salamander larva. Marbled salamanders and spotted salamanders are in the same genus, but they have different approaches to breeding. Marbled salamanders, Grunwald explains, lay their eggs in the fall “where they think a pond is going to be” instead of waiting for ephemeral pools to develop in spring. How do they decide where to lay eggs if the pond isn’t even there yet? Scientists aren’t sure, but salamanders “live in a chemical world,” Grunwald says, relying on taste and chemical signals.

Spotted salamander eggs and a marbled salamander larva, temporarily held in a plastic bag for viewing purposes.
Photo by Adam Kosinski, Wild Ones co-president.

Since marbled salamanders laid their eggs last fall, their larvae have had time to hatch and start developing, though they aren’t yet adults. Spotted salamanders, meanwhile, don’t breed until spring—when the ponds actually exist—so their eggs haven’t yet hatched. For the larvae of both species, developing in small, temporary ponds helps protect them from large predators like fish.

Both marbled and spotted salamanders are in a genus sometimes called mole salamanders because they live underground when they’re not breeding. “There’s an entire city underground here of burrows and holes and crevices,” Grunwald says, a “whole porous network of spaces.” The mole salamanders can shelter underground, but they can’t travel far without coming back to the surface. “It’s not a highway,” Grunwald says.

I would like to know what it is like to be a mole salamander, navigating by taste and smell and spending much of the year in small spaces underground.

Sam, a Wild Ones member, releasing the eggs back into the pond.

Before we left the forest, we went searching for lycophytes, an ancient lineage of plants that first evolved hundreds of millions of years ago. “In the Carboniferous Period 350 million years ago, these guys ruled,” Manos says. The lycophytes we saw in the Duke Forest were tiny, bright green sprigs in a small stream, but their ancestors were trees. Those ancient lycophyte trees are “responsible for all of the coal that we use,” says Manos. “The transformation of their organic material via millions of years of heat and pressure to metamorphic carbonized rock is the definition of coal.”

Quillwort, a modern-day descendant of ancient trees.

The lycophytes in the stream are members of the Isoetes genus, also known as quillworts. They look and feel much like grasses, but they are only distant relatives of true grasses. Grasses are flowering plants, while quillworts are lycophytes. Flowering plants and lycophytes diverged hundreds of millions of years ago. Lycophytes use spores to reproduce and have a life cycle similar to ferns. Even their leaves are anatomically and evolutionarily different from the leaves of flowering plants; lycophytes use “their own approach to making leaves,” according to Manos.

A representation of the evolutionary history of plants. Lycophytes, including the superficially grass-like quillwort we saw, are in the pteridophyte group, along with ferns. True grasses, on the other hand, are monocots, a branch of flowering plants.
Plant phylogeny.png, from Maulucioni via Wikimedia Commons, is licensed under the Creative Commons Attribution-Share Alike 4.0 International license.
By Sophie Cox

Post by Sophie Cox, Class of 2025

Warning: Birding Can Change You. Let It.

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On February 26, 2023

In Animals, Biology, Environment/Sustainability, Field Research, Science Communication & Education, Students

The Wild Ones, a student organization focused on enjoying and learning about nature, recently went to Flat River Waterfowl Compound to look for birds and my personal nemesis.

I have a nemesis (a bird that defies my searching). Actually, I have several, but I have been preoccupied with this particular nemesis for months.

I have seen an evening grosbeak exactly once, in a zoo, which emphatically does not count. For years, I have been fixated on-and-off (mostly on) with the possibility of seeing one in the wild.

Photo of a male evening grosbeak.
“Evening Grosbeak” by sedge23 is licensed under CC BY 2.0.

They have thick, conical beaks. The males are sunset-colored. (But good luck finding one at sunset, even though the first recorded sighting supposedly happened at twilight, hence their name.) I daydream about flocks of them descending on my bird feeders at home or wandering onto Duke’s campus. That hasn’t happened yet (unless it has happened while I have not been watching, an excruciating possibility I will simply have to live with).

Evening grosbeaks usually live in Canada and the northern U.S., but they are known to irrupt into areas farther south. Irruptions often occur in response to lower supplies of seeds and cones in a bird’s typical range, making it possible to predict bird irruptions, at least if you’re the famous finch forecaster. (Fun fact: “irrupt” literally means “break into,” whereas “erupt” means “break out.”)

Breaking news: The grosbeaks are in Durham, and they have been since December. I will wait while you perform any necessary reactions, including screaming, jumping up and down in delight, charging outside because you simply have to go find them right now, or telling me I must be mistaken.

I am not mistaken. There is a flock of evening grosbeaks overwintering at Flat River Impoundment, 11.8 miles from Duke University. I know this because I get hourly rare bird alerts by email, and I have been receiving emails about evening grosbeaks nearly every day for almost three months. Put another way, evening grosbeaks have been actively and no doubt intentionally taunting me for weeks on end.

Adam Kosinski, Wild Ones co-president, with binoculars.

Wild Ones, a student organization I’m involved with, had been thinking of organizing a birding trip. For reasons I will not even attempt to deny, I suggested Flat River Waterfowl Impoundment. Last Sunday, seven undergraduates drove there, armed with field guides and binoculars and visions of evening grosbeaks bursting into sight (okay, maybe that was just me).

Flat River Waterfowl Impoundment.
Photo by Adam Kosinski.

The morning was chilly but sunny. Flat River is a gorgeous, swampy place full of small ponds and stretches of long grass edged with trees. As soon as we got there, we were serenaded with birdsong: the high, musical trill of pine warblers, the haunting coo of mourning doves, lilting Carolina wren songs, and squeaky-dog-toy brown-headed nuthatch calls.

Photo by Adam Kosinski.

It wasn’t long before people got to experience the frustrating side of birding. We were admiring a sparrow in a ditch, trying to guess its identity. Someone pulled out a field guide and flipped through the sparrow section only to turn back to the bird and find it gone. Birds can fly. But fortunately, we’d collectively noticed enough field marks to feel reasonably confident identifying it as a swamp sparrow.

A white-throated sparrow, one of several that was feeding on the buds of this tree. Note the white throat and yellow lores.
Photo by Lydia Cox, Wild Ones member. (We are not related, if you’re wondering.)

We found two other sparrow species later: song sparrows and white-throated sparrows. Sparrows tend to be small, brownish, and streaky, but certain features can help distinguish some of the common species around here. I’m personally not very familiar with the swamp sparrow, but it has a rusty cap and gray face. The song sparrow has brown stripes on its head, extensive streaking on its underside, and a dark spot on its breast. The white-throated sparrow has striking black-and-white stripes on the top of its head, yellow lores on its face (the spot in front of the eye), and yes, a white throat. (Just don’t rely too much on bird names for identification. Red-bellied woodpeckers definitely have red heads but usually only have red bellies if you’re rather imaginative, but beware—they’re still red-bellied, not red-headed woodpeckers. Meanwhile, there are dozens of warblers with yellow on them, but only one of them is a yellow warbler. Nashville warblers only pass through Nashville during migration, and American robins aren’t robins at all.)

A Cooper’s hawk with prey between its talons. Note the gray wings, the red barring on the bird’s underside, the dark bands on its tail, and the red eye.
Photo by Lydia Cox.

We saw Carolina chickadees flitting through trees, an Eastern phoebe doing its characteristic tail-wagging, and a Cooper’s hawk feeding on prey. Then, thrillingly, we spotted a bald eagle soaring through the sky. The bald eagle, America’s national bird since 1782, was in danger of extinction for years, largely due to the insecticide DDT, which made their eggs so thin that even being incubated by their parents could make them crack. However, the bald eagle was removed from the endangered species list in 2007, and populations have continued to increase.

A bald eagle in flight.
Photo by Lydia Cox.

Not long after the eagle sighting, we saw another flying raptor: an osprey. In fact, it must have been a good day for raptors because by the end of our trip we had recorded one osprey, two Cooper’s hawks, three bald eagles, and two red-tailed hawks.

We also saw a lot of birders—perhaps two dozen others, maybe more, not counting our own group. Each time we passed a group going in the opposite direction, I asked them if they’d found the grosbeaks.

A bald eagle nest.
Photo taken with my phone through my binoculars, a technique that is slowly teaching me a modicum of patience.

I think everyone I asked had seen them, and they were all eager to point us in the right direction. Birders like to use landmarks like “by the eagles’ nest” and “the fifth pine on the right” and  “past the crossbills.” We found the eagles’ nest, with help from some of the local birders. We think we found the fifth pine on the right, but there were a lot of pines there, so we’re not sure.

We did not find the red crossbills, another irruptive bird species overwintering here this year. (Crossbills are aptly named. The tips of their mandibles really do cross, which helps them access seeds inside cones.)

Red crossbills, another irruptive bird species, have also been overwintering at Flat River Waterfowl Impoundment, but Wild Ones did not see them.
“Red Crossbills (Male)” by Elaine R. Wilson, www.naturespicsonline.com is licensed under CC BY-SA 3.0.

We found the spot where the evening grosbeaks had most recently been seen — just twenty minutes before we got there, according to the people we were talking to. We waited. We scrutinized the pine trees. We watched red-tailed hawks and bald eagles circle high above us. We admired the eagles’ nest, a huge collection of sticks high in a pine tree.

Adam Kosinski and Abby Saks, making sure there were no birds hiding underwater. (They were actually looking at interesting water creatures like crayfish and tadpoles.)

Would you like to guess what we did not find? My nemesis. Because the evening grosbeaks have devious minds and clearly flew all the way to Durham with the sole intent of hiding from me, dodging me, flying away as soon as I approached, and flying back again as soon as I was gone. (No, really. Other people reported them at Flat River that same day, both before and after our trip there.)

From left: Ethan Rehder, Barron Brothers, Sophie Cox, Gurnoor Majhail (Wild Ones co-president), and Lydia Cox.
Photo by Adam Kosinski.

Birding can be intensely frustrating. It can plant images in your mind that will haunt you and taunt you for the rest of your life. Like, for instance, the tiny blue bird I caught a brief glimpse of in the trees one early morning in Yellowstone. For years, I wondered if it could have been a cerulean warbler, but cerulean warblers don’t live in the western U.S. Or let’s talk about the green bird—yes, I swear it was green; no, I can’t prove it—that came to my bird feeders several years ago and never came back. Not while I was watching, anyway. The only thing I can think of for that one is a female painted bunting, but painted buntings aren’t usually in upstate South Carolina. (If my local volunteer eBird reviewer in South Carolina ever happens to read this, I promise I won’t report either of those mystery sightings to eBird.) Or, of course, the evening grosbeaks that flew away twenty minutes before we arrived.

Birding can also be thrilling, meditative, and by all accounts wonderful. Yes, that little blue bird in Yellowstone and the maybe-green one in my backyard are branded in my memory, as are countless more moments of maybe and almost and what if? I will never know what they were. I will probably never get over it.

But there are other moments that stick in my mind just as clearly. The bald eagle soaring above us on this Wild Ones trip. The black-capped chickadee that landed on my finger years ago while my brother and I rested our hands on a bird feeder and waited to see what would happen. My first glimpse of a black-throated blue warbler (I am so proud of whoever named that bird species), chasing an equally tiny Carolina chickadee in my backyard.

Warbler illustrations by James Ellsworth De Kay, a zoologist who described hundreds of animal species in the 19th century. From top to bottom: black-throated blue warbler, Cape May warbler, and Nashville warbler.
“131. The Black-throated Blue Warbler (Sylvicola canadensis) 132. He Cape-May Warbler (Sylvicola maritima) 133. The Nashville Warbler (Syvicola ruficapilla) illustration from Zoology of New york (1842 – 1844) by James Ellsworth De Kay (1792-1851).” by Free Public Domain Illustrations by rawpixel is licensed under CC BY 2.0.

The Cape May warbler I saw with a close friend in a small field covered in purple wildflowers. The first time I heard the loud, ringing Teacher-teacher-teacher! song of the ovenbird. A blackpoll warbler, the first I’d ever seen, in a grove of trees in a swampy field that only birders seem to find reason to visit.

The moment two Carolina wrens took food from my hand for the first time. Prothonotary warblers (another nemesis bird) practically dripping from the trees on a rainy, buggy hike along a boardwalk. The downy woodpecker that landed on my gloved hand, apparently too impatient to wait for me to finish what I was doing with the suet feeder, and pecked at the suet with that sharp beak, her black tongue flicking in and out, her talons clinging to me with a trust that brought tears to my eyes.

Birding can change you. It can make your world come alive in a whole new way. It can make traveling somewhere new feel all the more magical — a new soundscape, new flashes of colors and patterns, a new set of beings that make a place what it is. In the same way, birding can make home feel all the more like home. Even when I can’t name all the birds that are making noise in my yard, there is a familiarity to their collective symphony, a comforting sense of “You are here.” I encourage you to watch and listen to birds, too, to join the quasi-cult that birding can be, to trek through somewhere wet and dark when the sky is just beginning to lighten—or to simply step outside, wherever you are, and listen and watch and wait right here and right now. You don’t even need to know their names (though once you start, good luck stopping). And you certainly don’t need a nemesis bird. In fact, your birding experience will be calmer without one. But that might not be up to you, in the end. Nemesis birds have minds of their own.

Post by Sophie Cox, Class of 2025

Recovery, Resilience, and Coexistence: Nature-based Solutions on the Coast

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On February 10, 2023

In Animals, Biology, Climate/Global Change, Environment/Sustainability, Faculty, Field Research, Lecture, Oceans, Policy

When it comes to balancing the needs of humans and the needs of nature, “Historically it was ‘develop or conserve’ or ‘develop or restore,’” says Carter Smith, Ph.D., a Lecturing Fellow in the Division of Marine Science & Conservation who researches coastal restoration.

However, according to Brian Silliman, Ph.D., Rachel Carson Distinguished Professor of Marine Conservation Biology, “We are having a new paradigm shift where it’s not just… ‘nature over here’ and ‘humans over here.’”

Instead, conservation initiatives are increasingly focusing on coexistence with nature and ecological resilience, according to this panel discussion of marine science experts during Duke Research and Innovation Week 2023.

Nature-based solutions — protecting and restoring natural shoreline habitats — have a proven role in protecting and restoring coastal ecosystems. According to the International Union for Conservation of Nature (IUCN), “Nature-based solutions… address societal challenges effectively and adaptively, simultaneously benefiting people and nature.”

The panel, moderated by Andrew J. Read, Ph.D., Stephen A. Toth Distinguished Professor of Marine Biology and Professor of Marine Conservation Biology, also included Brian Silliman, Carter Smith, and Stephanie Valdez, a Ph.D. Student in Marine Science & Conservation.

Living shorelines can help protect coastal ecosystems from storms while also offering benefits for climate and conservation. Photos by Carter Smith.

According to Smith, nature-based solutions can “leverage nature and the power of healthy ecosystems to protect people” while also preserving biodiversity and mitigating climate change. She spoke about living shorelines as an effective and ecologically responsible way to protect coastal ecosystems.

“The traditional paradigm in coastal protection is that you build some kind of hard, fixed structure” like a seawall, Smith said, but conventional seawalls can have negative effects on biodiversity, habitats, nutrient cycling, and the environment at large. “In this case, coastal protection and biodiversity really are at odds.”

After multiple hurricanes, living shorelines had significantly less visible damage or erosion than sites with conventional hardscape protection, like seawalls.

Nicholas Lecturing Fellow Carter Smith

That’s where living shorelines come in. Living shorelines incorporate plants and natural materials like sand and rock to stabilize coastal areas and protect them from storms while also creating more natural habitats and minimizing environmental destruction. But “if these structures are actually going to replace conventional infrastructure,” Smith says, it’s important to show that they’re effective.

Smith and colleagues have studied how living shorelines fared during multiple hurricanes and have found that living shorelines had significantly less “visible damage or erosion” compared to sites with conventional storm protection infrastructure.

After Hurricane Matthew in 2016, for instance, both natural marshes and conventional infrastructure (like seawalls) lost elevation due to the storm. Living shorelines, on the other hand, experienced almost no change in elevation.

Smith is also investigating how living shorelines may support “community and psychosocial resilience” along with their benefits to biodiversity and climate. She envisions future community fishing days or birdwatching trips to bring people together, encourage environmental education, and foster a sense of place.

PhD student Stephanie Valdez then spoke about the importance of coastal ecosystems.

“Blue carbon ecosystems,” which include sea grasses, marshes, and mangroves, provide services like stabilizing sediments, reducing the destructive force of powerful waves, and storing carbon, she said. These ecosystems can bury carbon much faster than terrestrial ecosystems, which has important implications when it comes to climate change.

In the atmosphere, carbon dioxide and other greenhouse gasses contribute to global warming, but plants pull carbon dioxide out of the air during photosynthesis and convert it to carbohydrates, releasing oxygen as a byproduct. Therefore, ecosystems rich in fast-growing plants can serve as carbon sinks, reducing the amount of atmospheric carbon, Valdez explained.

Unfortunately, blue carbon ecosystems have suffered significant loss from human activities and development. We’ve replaced these wild areas with farms and buildings, polluted them with toxins and waste, and decimated habitats that so many other creatures rely on. But given the chance, these places can sometimes grow back. Valdez discussed a 2013 study which found that seagrass restoration led to a significantly higher carbon burial rate within just a few years.

Sea grasses, marshes, and mangroves provide services like stabilizing sediments, reducing the destructive force of powerful waves, and storing carbon.

PhD Student Stephanie Valde

Valdez also talked about the importance of recognizing and encouraging natural ecological partnerships within and between species. Humans have taken advantage of such partnerships before, she says. Consider the “Three Sisters:” beans, corn, and squash, which Native Americans planted close proximity so the three crops would benefit each other. Large squash leaves could provide shade to young seedlings, beans added nitrogen to the soil, and cornstalks served as a natural beanpole.

Recognizing that mutualistic relationships exist in natural ecosystems can help us preserve habitats like salt marshes. Valdez points to studies showing that the presence of oysters and clams can positively impact seagrasses and marshes. In restoration, it’s important “that we’re not focusing on one species alone but looking at the ecosystem as a whole”—from top predators to “foundation species.”

“There is hope for successful restoration of these vital ecosystems and their potential to aid in climate change mitigation,” Valdez said.

Finally, Prof. Brian Silliman discussed the role of predators in wider ecosystem restoration projects. Prioritizing the protection, restoration, and sometimes reintroduction of top predators isn’t always popular, but Silliman says predators play important roles in ecosystems around the world.

“One of the best examples we have of top predators facilitating ecosystems and climate change mitigation are tiger sharks in Australia,” he says. When the sharks are around, sea turtles eat fewer aquatic plants. “Not because [the sharks] eat a lot of sea turtles but because they scare them toward the shoreline,” reducing herbivory.

However, Silliman said it’s unclear sometimes whether the existence of a predator is actually responsible for a given benefit. Other times, though, experiments provide evidence that predators really are making a difference. Silliman referenced a study showing that sea otters can help protect plants, like seagrasses, in their habitats.

Restoring or reintroducing top predators in their natural habitats can help stabilize ecosystems impacted by climate change and other stressors.

And crucially, “Predators increase stress resistance.” When physical stressors reach a certain point in a given ecosystem, wildlife can rapidly decline. But wildlife that’s used to coexisting with a top predator may have a higher stress threshold. In our ever-changing world, the ability to adapt is as important as ever.

“I think there is great optimism and opportunity here,” Silliman says. The other speakers agree. “Right now,” Valdez says, “as far as restoration and protection goes, we are at the very beginnings. We’re just at the forefront of figuring out how to restore feasibly and at a level of success that makes it worth our time.”

Restoring or reintroducing top predators in their natural habitats can help stabilize ecosystems impacted by climate change and other stressors.

Brian Silliman

Smith emphasized the important role that nature-based solutions can play. Even in areas where we aren’t achieving the “full benefit of conserving or restoring a habitat,” we can still get “some benefit in areas where if we don’t use nature-based solutions,” conservation and restoration might not take place at all.

According to Valdez, “Previously we would see restoration or… conservation really at odds with academia itself as well as the community as a whole.” But we’re reaching a point where “People know what restoration is. People know what these habitats are. And I feel like twenty or thirty years ago that was not the case.” She sees “a lot of hope in what we are doing, a lot of hope in what is coming.”

“There’s so much that we can learn from nature… and these processes and functions that have evolved over millions and millions of years,” Smith adds. “The more we can learn to coexist and to integrate our society with thriving ecosystems, the better it will be for everyone.”

Post by Sophie Cox, Class of 2025

On-Stage Neuroscience with Cockroach Brains …and Legs

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On February 7, 2023

In Animals, Neuroscience, Science Communication & Education

A low buzzing erupts into a loud static noise that fills the Duke lecture hall.

University of Michigan neuroscientist Gregory Gage describes the noise as the “most beautiful sound in the world.” It’s not the sound itself that evokes such fascination, but the source: this is the sound of electrical signals coming from neurons inside an amputated cockroach leg. 

With a background in electrical engineering, Gage credits this sound as the moment that got him interested in neuroscience. He now travels the country as an educator to bring his experiments to the public and encourage interest in neuroscience. His organization, Backyard Brains aims to bring research outside of the lab, and make it accessible to children and students everywhere. On Feb. 2, he presented the Gastronauts Seminar in the Nanaline Duke Building.

His first on-stage experiment aims to understand how information is encoded inside neurons, specifically the neurons located inside the barbs on cockroach legs. In order to record the signals without the roach running off, the first step is to amputate the cockroach leg. For all those worried for the well-being of the roach, rest assured that it was first “anesthetized” in a bath of ice water. (It’s still up for debate if cockroaches can truly feel pain, but Gage likes to err on the side of caution). Importantly, cockroaches also have the ability to regenerate limbs. In about five weeks a new leg will start to grow to replace the one that has been lost, and the entire regrowth will be completed in about 3 to 5 months. 

Underneath each hair on the leg of a cockroach, there is a neuron that detects stimuli and sends electrical impulses up to the brain.

The second step is to place electrode pins through the legs. Two pins are required so that the current will flow through the leg. One pin is located where there are very few neurons, serving as the ‘ground.” This experiment will measure the difference between the two pins, multiplied by the gain provided by an amplifier which makes the signal easier to see and hear. 

Turning up a volume knob on the amplifier, a low static buzzing becomes audible throughout the lecture hall. As Gage is the first to admit, “it doesn’t sound like much” at first. There are a few possibilities: maybe there is no neuron activity, maybe the leg is dead, or maybe it’s just not stimulated. The leg barbs contain stretch receptors: important sensory structures that play critical roles in detecting vibration, pressure, and touch.

These receptors are a type of ion channel, which are proteins located in the plasma membrane of cells that form a passageway through the membrane. They have the ability to open and close in response to chemical or mechanical signals. Stretch-activated ion channels respond to membrane deformation. When compressed, they allow ions to flow through, creating an immediate change in the transmembrane gradient and allowing for a rapid signaling response. The flow of ions is a flow of charge, and constitutes an electric current.

The opening and closing of ion channels underlie all electrical signaling of nerves and muscles. Why has the nervous system evolved to use electricity (as opposed to a chemical diffusion process)? Because it’s fast. And often our lives (or that of a cockroach) depend on responding quickly.

At the direction of Gage, a volunteer lightly brushes the cockroach leg. Suddenly, a change in the noise: short static bursts in volume correspond with each stroke of the cockroach leg. These are “single-unit recordings,” a sampling of the activity of individual or small clusters of neurons. The sound we are hearing is a burst of activity: the neurons rapidly firing in response to the stimuli, and attempting to send the electrical message up the brain.

Dr. Gage points out the spikes, or action potentials, associated with the firing of neurons in the roach’s leg.

Next, Gage pulls up his screen and shows a visual representation of the electrical signals. Along with the sound, it is clear to see the large spikes that correspond with the neurons firing. These spikes are called action potentials, and they occur when the membrane potential of a specific cell location rapidly rises and falls. When touching the leg hairs with more pressure, the number of action potentials per second increases. Measuring the number of spikes that occur per second is called rate coding, and it can be used to answer complex questions about how neurons respond to stimuli.

This experiment demonstrated how neurons send electrical impulses to the brain. But the brain does not just receive electrical impulses, it also sends them out. What happens if we tried to simulate the electrical impulses sent by the brain to the cockroach’s leg? In his second on-stage experiment, Gage demonstrates exactly this, using hip-hop music from his iPod as his electrical current.

The buds of a pair of headphones are cut off and replaced with small clips that attach to the electrode pins sticking out of the leg. Dr. Gage presses play on the music on his iPod, and immediately, the end of the cockroach leg begins to twitch and jump. The leg moves most dramatically with the bass of the music: lower frequencies have the longest waves, which correspond to the largest amount of current. 

You can watch Dr. Gage perform the “cockroach beatbox” experiment live on stage in one of his Ted Talks.

One final experiment combines both of the previous ones: how nerves encode information, and how nerves can be stimulated. A group of undergraduates at the University of Chile developed a system that uses an app to control the mind of a roach. Cockroaches use their antennae to observe the environment around them. If you take a cockroach and fit a wire inside each antenna (think of them like hollow tubes filled with neurons), you can stimulate those neurons, tricking the cockroach brain into thinking it has detected an outside stimulus. Using an Arduino microcontroller, the team of students created a little “hat” for the cockroach, and connected it via bluetooth to a smartphone app that can be used to send electrical impulses. Stimulating the right antennae causes the cockroach to move to the left, and stimulating the left antennae causes the cockroach to move to the right.

The RoboRoach device uses a smartphone app to perform “mind control” on the roach.

Why a cockroach? It’s a question that a volunteer stops to ask after finding herself up close and personal with the creature. Gage explains that they actually have brains very similar to our own. If we can learn “a little about how their brain works, we’re gonna learn a lot about ours.”

He ends his presentation with a parting message to all the researchers in the room: “I spend my life working on weird things like this, because each one tells a little story. Through these stories we can bring experiments to classrooms, democratize science and make it more accessible to everyone.”

Post by Kyla Hunter

Post by Kyla Hunter, Class of 2023

Some Primates Are More Susceptible to Parasites Than Others. Researchers Are Using New Methods to Find Out Why.

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On January 30, 2023

In Animals, Climate/Global Change, Guest Post, Medicine

Chimpanzees are among the best studied primates for parasite interactions. Photo credit: Wikimedia Commons

Fleas, tapeworms, Giardia, pinworms:  Parasites are all around us. But some animals are more susceptible than others. Take the well-studied chimpanzee, for example: it’s known to host over 100 parasites. In contrast, species like the indri, a lemur only found on Madagascar, are only known to host about 10 parasites. Many other primates are so poorly studied that only one parasite has ever been recorded.

Relative to the chimpanzee, the indri is poorly known for its parasites. Credit: James Herrera.

In a new study published in the Journal of Animal Ecology, we examined which traits of both primates and parasites predict the likelihood of their interactions. Using advanced techniques in social network analysis, called the exponential random graph, we were able to simultaneously test the traits of primates and parasites to determine what predisposes primates to infection and what gives some parasites a unique advantage.

For primates, larger species that are found in warmer, wetter climates are more likely to host diverse parasites, compared to smaller species living in drier, cooler climates. Further, species in the same branches of the evolutionary tree and those that live in the same geographic region are more likely to share parasites than more distantly related species found on different continents. Viruses, protozoa, and helminth worms are more likely to infect diverse primates than fungi, arthropods, and bacteria. Parasites that are known to infect non-primate mammals are also more likely to infect diverse primates.

A photo from a microscope slide showing the blood parasite Plasmodium falciparum. One of the pathogens that causes malaria, P. falciparum also infects 118 other primates. In contrast, there are at least 30 other kinds of Plasmodium that only infect one or a few primates and their disease effects are poorly understood. Photo credit: Wikimedia Commons.

These new results were made possible by the great advances being made in infectious disease ecology. Over the last two decades, Dr. Charles Nunn at Duke University’s Evolutionary Anthropology and Global Health departments has been working with teams of researchers to compile all published records of primate-parasite interactions. Combing through the literature, almost 600 published sources were obtained to glean which parasites are found in over 200 primates species, with over 2,300 interactions recorded. With the analytical tools in social network science mastered by Duke Sociology professor Dr. James Moody, we were able to systematically test how traits of both hosts and parasites affect the likelihood of their interaction for the first time. While many previous studies used subsets of this database and examined either hosts or parasites in isolation, we were able to make new inferences about the critical links in this unique ecological network.

This work builds on a recent study that showed how extinction of primate hosts could lead to the co-extinction of almost 200 parasite species. While at first this might seem like a good thing, in fact it could have negative impacts on biodiversity as a whole. Many parasites don’t actually cause disease or death in the hosts, and some may even have beneficial properties. We simply don’t know enough about these critical and co-evolved relationships to understand what effects host-parasite coextinctions could have in the long-term.

While it might seem strange to worry about parasite extinctions, they are actually an important part of biodiversity and ecosystem functions. Understanding how primates and parasites interact reveals new insights into coevolutionary theory, and could also contribute to the conservation of underappreciated species richness. While from a public health perspective, we’d like to see some parasites disappear, like corona and ebola viruses, from an evolutionary stance, the sheer diversity of parasites and their intimate relationships with their hosts make them fascinating and crucial components of biodiversity.

By James Herrera, Ph.D., Duke Lemur Center SAVA Conservation Initiative

Rewilding the Gut

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On January 6, 2023

In Animals, Field Research, Genetics/Genomics, Lemurs, Medicine

Processed foods and overuse of antibiotics can wreak havoc on the trillions of bacteria and other microbes that inhabit the gut. A new study of the gut microbiomes of lemurs looks at whether reconnecting with nature can help restore this internal ecosystem to a more natural state. Credit: Sally Bornbusch.

Modern life messes with the microbiome -– the trillions of bacteria and other microbes that live inside the body. Could reconnecting with nature bring this internal ecosystem back into balance?

A new study suggests it can, at least in lemurs. Led by Duke Ph.D. alumnus Sally Bornbusch and her graduate advisor Christine Drea, the research team collected fecal samples from more than 170 ring-tailed lemurs living in various conditions in Madagascar: some were living in the wild, some were kept as pets, and some were rescued from the pet and tourism industries and then relocated to a rescue center in southwestern Madagascar where they ate a more natural diet and had less exposure to people.

Collecting fecal samples in Madagascar

Then the researchers sequenced DNA from the fecal samples to identify their microbial makeup. They found that the longer lemurs lived at the rescue center, the more similar their gut microbes were to those of their wild counterparts. Former pet lemurs with more time at the rescue center also showed fewer signs of antibiotic resistance.

By “rewilding” the guts of captive animals, researchers say we may be able to better prime them for success, whether after rescue or before translocation or reintroduction into the wild.

This research was supported by grants from the National Science Foundation (1945776, 1749465), the Triangle Center for Evolutionary Medicine, Duke’s Kenan Institute for Ethics, the Margot Marsh Biodiversity Fund and Lemur Love.

CITATION: “Microbial Rewilding in the Gut Microbiomes of Captive Ring-Tailed Lemurs (Lemur catta) in Madagascar,” Sally L. Bornbusch, Tara A. Clarke, Sylvia Hobilalaina, Honore Soatata Reseva, Marni LaFleur & Christine M. Drea. Scientific Reports, Dec. 27, 2022. DOI: 10.1038/s41598-022-26861-0.

Robin Smith
By Robin Smith

Traveling With Friends Helps Even Mixed-Up Migrators Find Their Way

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On December 6, 2022

In Animals, Behavior/Psychology, Biology, Climate/Global Change

North American monarch butterflies migrate each winter to just a few mountaintops in central Mexico, with help from an internal compass that guides them home. New computer modeling research offers clues to how migrating animals get to where they need to go, even when their magnetic compass leads them astray. Credit: Jesse Granger, Duke University

DURHAM, N.C. — Some of us live and die by our phone’s GPS. But if we can’t get a signal or lose battery power, we get lost on our way to the grocery store.

Yet animals can find their way across vast distances with amazing accuracy.

Take monarch butterflies, for example. Millions of them fly up to 2,500 miles across the eastern half of North America to the same overwintering grounds each year, using the Earth’s magnetic field to help them reach a small region in central Mexico that’s about the size of Disney World.

Or sockeye salmon: starting out in the open ocean they head home each year to spawn. Using geomagnetic cues they manage to identify their home stream from among thousands of possibilities, often returning to within feet of their birthplace.

Now, new research offers clues to how migrating animals get to where they need to go, even when they lose the signal or their inner compass leads them astray. The key, said Duke Ph.D. student Jesse Granger: “they can get there faster and more efficiently if they travel with a friend.”

When their internal compasses go bad, migrating animals like these sockeye salmon don’t stop to ask directions. But they succeed if they stay with their fellow travelers. Credit: Jonny Armstrong, USGS

Many animals can sense the Earth’s magnetic field and use it as a compass. What has puzzled scientists, Granger said, is the magnetic sense is not fail-safe. These signals coming from the planet’s molten core are subtle at the surface. Phenomena such as solar storms and man-made electromagnetic noise can disrupt them or drown them out.

It’s as if the ‘needle’ of their inner compass sometimes gets thrown off or points in random directions, making it hard to get a reliable reading. How do some animals manage to chart a course with such a noisy sensory system and still get it right?

“This is the question that keeps me up at night,” said Granger, who did the work with her adviser, Duke Biology Professor Sönke Johnsen.

Multiple hypotheses have been put forward to explain how they do it. Perhaps, some scientists say, migrating animals average multiple measurements taken over time to get more accurate information.

Or maybe they switch from consulting their magnetic compass to using other ways of navigating as they near the end of their journey — such as smell, or landmarks — to narrow in on their goal.

In a paper published Nov. 16 in the journal Proceedings of the Royal Society B, the Duke team wanted to pit these ideas against a third possibility: That some animals still manage to find their way, even when their compass readings are unreliable, simply by sticking  together.

To test the idea, they created a computer model to simulate virtual groups of migrating animals, and analyzed how different navigation tactics affected their performance.

The animals in the model begin their journey spread out over a wide area, encountering others along the route. The direction an animal takes at each step along the way is a balance between two competing impulses: to band together and stay with the group, or to head towards a specific destination, but with some degree of error in finding their bearings.

The scientists found that, even when the simulated animals started to make more mistakes in reading their magnetic map, the ones that stuck with their neighbors still reached their destination, whereas those that didn’t care about staying together didn’t make it.

“We showed that animals are better at navigating in a group than they are at navigating alone,” Granger said.

Even when their magnetic compass veered them off course, more than 70% of animals in the model still made it home, simply by joining with others and following their lead. Other ways of compensating didn’t measure up, or would need to guide them perfectly for most of the journey to accomplish the same feat.

But the strategy breaks down when species decline in number, the researchers found. The team showed that animals who need friends to find their way are more likely to get lost when their population shrinks below a certain density.

Prior to the 1950s, tens of thousands of Kemp’s ridley sea turtles could be seen nesting near Rancho Nuevo, Mexico on a single day. By the mid-1980s the number of nesting females had dropped to a few hundred.

“If the population density starts dropping, it takes them longer and longer along their migratory route before they find anyone else,” Granger said.

Previous studies have made similar predictions, but the Duke team’s model could help future researchers quantify the effect for different species. In some runs of the model, for example, they found that if a hypothetical population dropped by 50% — akin to what monarchs have experienced in the last decade, and some salmon in the last century — 37% fewer of the remaining individuals would make it to their destination.

“This may be an underappreciated aspect of concern when studying population loss,” Granger said.

This research was supported in part by the Air Force Office of Scientific Research (FA9550-20-1-0399) and by a National Defense Science & Engineering Graduate Fellowship to Jesse Granger.

CITATION: “Collective Movement as a Solution to Noisy Navigation and its Vulnerability to Population Loss,” Jesse Granger and Sönke Johnsen. Proceedings of the Royal Society B, Nov. 16, 2022. DOI: 10.1098/rspb.2022.1910

Robin Smith
By Robin Smith

Why Do Some Dogs Need High Chairs, and How Can Genetics Help?

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On November 17, 2022

In Animals, Biology, Genetics/Genomics, Lecture, Medicine

Jake, a German shepherd dog in a Bailey chair. Dogs with megaesophagus must eat in a vertical position to help food travel to their stomachs.
Photo credit: Beth Grant

Some dogs have to eat in a high chair—or, more specifically, a Bailey Chair. The chair keeps them in a vertical position while they eat so that gravity can do the work their bodies can’t: moving food from the mouth to the stomach.

These dogs have megaesophagus, an esophagus disorder that can prevent dogs from properly digesting food and absorbing nutrients. When you swallow a bite of food, it travels down a muscular tube, the esophagus, to the stomach. In humans, the esophagus is vertical, so our esophageal muscles don’t have to fight against gravity. But because dogs are quadrupeds, a dog’s esophagus is more horizontal, so “there is a greater burden on peristaltic contractions to transport the food into the stomach.” In dogs with megaesophagus, the esophagus is dilated, and those contractions are less effective. Instead of moving properly into the stomach, food can remain in the esophagus, exacerbating the problem and preventing proper digestion and nutrient absorption. 

Leigh Anne Clark, Ph.D., an associate professor at Clemson University, recently spoke at Duke about megaesophagus in dogs and its genetic underpinnings. She has authored dozens of publications on dog genetics, including five cover features. Her research primarily involves “[mapping] alleles and genes that underlie disease in dogs.” In complex diseases like megaesophagus, that’s easier said than done. “This disease has a spectrum,” Clark says, and “Spoiler: that makes it more complicated to map.”

Clinical signs of megaesophagus, or mega for short, include regurgitation, coughing, loss of appetite, and weight loss. (We might use the word “symptom” to talk about human conditions, but “a symptom is something someone describes—e.g., I feel nauseous. But dogs can’t talk, so we can only see ‘clinical signs.’”) Complications of mega can include aspiration pneumonia and, in severe cases, gastroesophageal intussusception, an emergency situation in which dogs “suck their stomach up into their esophagus.”

Leigh Anne Clark of Clemson University

Sometimes megaesophagus resolves on its own with age, but when it doesn’t it requires lifelong management. Mega has no cure, but management can involve vertical feeding, smaller and more frequent meals, soft foods, and sometimes medication. Even liquid water can cause problems, so some dogs with mega receive “cubed water,” made by adding a “gelatinous material” to water, instead of a normal water bowl.

In dogs, mega can be either congenital, meaning present at birth, or acquired. In cases of acquired megaesophagus, the condition is “usually secondary to something else,” and the root cause is often never determined. (Humans can get mega, too, but as with acquired mega in dogs, mega in humans is usually caused by a preexisting condition. The best human comparison, according to Clark, might be achalasia, a rare disorder that causes difficulty swallowing.) Clark’s current research focuses on the congenital form of the disease in dogs.

Her laboratory recently published a paper investigating the genetic foundation of mega. Unlike some diseases, mega isn’t caused by just one genetic mutation, so determining what genes might be at play required some genetic detective work. “You see mega across breeds,” Clark says, which suggests an environmental component, but the disease is more prevalent in some breeds than others. For instance, 28 percent of all diagnoses are in German shepherds. That was a “red flag” indicating that genes were at least partly responsible.

Clark and her collaborators chose to limit their research study to German shepherds. Despite including a wide range of dogs in the study, they noticed that males were significantly overrepresented. Clark thinks that estrogen, a hormone more abundant in females, may have a protective effect against mega.

Clark and her team performed a genome-wide association study (GWAS) to look for alleles that are more common in dogs with mega. One allele that turned out to be a major risk factor was a variant of the MCHR2 gene, which plays a role in feeding behaviors. In breeds where mega is overrepresented, like German shepherds, “we have a situation where the predominant allele in the population is also the risk allele,” says Clark.

Using the results of the study, they developed a test that can identify which version of the gene a given dog has. The test, available at veterinary testing companies, is designed “to help breeders reduce the frequency of the risk allele and to plan matings that are less likely to produce affected puppies.”

Post by Sophie Cox, Class of 2025

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