The H5N1 bird flu situation in the US seems more fraught than ever this week as the virus continues to spread swiftly in dairy cattle and birds while sporadically jumping to humans.
On Monday, officials in Louisiana announced that the person who had developed the country’s first severe H5N1 infection had died of the infection, marking the country’s first H5N1 death. Meanwhile, with no signs of H5N1 slowing, seasonal flu is skyrocketing, raising anxiety that the different flu viruses could mingle, swap genetic elements, and generate a yet more dangerous virus strain.
But, despite the seemingly fever-pitch of viral activity and fears, a representative for the World Health Organization today noted that risk to the general population remains low—as long as one critical factor remains absent: person-to-person spread.
“We are concerned, of course, but we look at the risk to the general population and, as I said, it still remains low,” WHO spokesperson Margaret Harris told reporters at a Geneva press briefing Tuesday in response to questions related to the US death. In terms of updating risk assessments, you have to look at how the virus behaved in that patient and if it jumped from one person to another person, which it didn’t, Harris explained. “At the moment, we’re not seeing behavior that’s changing our risk assessment,” she added.
In a statement on the death late Monday, the US Centers for Disease Control and Prevention emphasized that no human-to-human transmission has been identified in the US. To date, there have been 66 documented human cases of H5N1 infections since the start of 2024. Of those, 40 were linked to exposure to infected dairy cows, 23 were linked to infected poultry, two had no clear source, and one case—the fatal case in Louisiana—was linked to exposure to infected backyard and wild birds.
We can get a drone to fly like a pigeon, but we needed to use feathers to do it.
Pigeons manage to get vertical without using a vertical tail. Credit: HamidEbrahimi
Most airplanes in the world have vertical tails or rudders to prevent Dutch roll instabilities, a combination of yawing and sideways motions with rolling that looks a bit like the movements of a skater. Unfortunately, a vertical tail adds weight and generates drag, which reduces fuel efficiency in passenger airliners. It also increases the radar signature, which is something you want to keep as low as possible in a military aircraft.
In the B-2 stealth bomber, one of the very few rudderless airplanes, Dutch roll instabilities are dealt with using drag flaps positioned at the tips of its wings, which can split and open to make one wing generate more drag than the other and thus laterally stabilize the machine. “But it is not really an efficient way to solve this problem,” says David Lentink, an aerospace engineer and a biologist at the University of Groningen, Netherlands. “The efficient way is solving it by generating lift instead of drag. This is something birds do.”
Lentink led the study aimed at better understanding birds’ rudderless flight mechanics.
Automatic airplanes
Birds flight involves near-constant turbulence—“When they fly around buildings, near trees, near rocks, near cliffs,” Lentink says. The leading hypothesis on how they manage this in a seemingly graceful, effortless manner was suggested by a German scientist named Franz Groebbels. He argued that birds’ ability relied on their reflexes. When he held a bird in his hands, he noticed that its tail would flip down when the bird was pitched up and down, and when the bird was moved left and right, its wings also responded to movement by extending left and right asymmetrically. “Another reason to think reflexes matter is comparing this to our own human locomotion—when we stumble, it is a reflex that saves us from falling,” Lentink claims.
Groebbels’ intuition about birds’ reflexes being responsible for flight stabilization was later backed by neuroscience. The movements of birds’ wings and muscles were recorded and found to be proportional to the extent that the bird was pitched or rolled. The hypothesis, however, was extremely difficult to test with a flying bird—all the experiments aimed at confirming it have been done on birds that were held in place. Another challenge was determining if those wing and tail movements were reflexive or voluntary.
“I think one pretty cool thing is that Groebbels wrote his paper back in 1929, long before autopilot systems or autonomous flight were invented, and yet he said that birds flew like automatic airplanes,” Lentink says. To figure out if he was right, Lentink and his colleagues started with the Groebbels’s analogy but worked their way backward—they started building autonomous airplanes designed to look and fly like birds.
Reverse-engineering pigeons
The first flying robot Lentink’s team built was called the Tailbot. It had fixed wings and a very sophisticated tail that could move with five actuated degrees of freedom. “It could spread—furl and unfurl—move up and down, move sideways, even asymmetrically if necessary, and tilt. It could do everything a bird’s tail can,” Lentink explains. The team put this robot in a wind tunnel that simulated turbulent flight and fine-tuned a controller that adjusted the tail’s position in response to changes in the robot’s body position, mimicking reflexes observed in real pigeons.
“We found that this reflexes controller that managed the tail’s movement worked and stabilized the robot in the wind tunnel. But when we took it outdoors, results were disappointing. It actually ended up crashing,” Lentink says. Given that relying on a morphing tail alone was not enough, the team built another robot called PigeonBot II, which added pigeon-like morphing wings.
Each wing could be independently tucked or extended. Combined with the morphing tail and nine servomotors—two per wing and five in the tail—the robot weighed around 300 grams, which is around the weight of a real pigeon. Reflexes were managed by the same controller that was modified to manage wing motions as well.
To enable autonomous flight, the team fitted the robot with two propellers and an off-the-shelf drone autopilot called Pixracer. The problem with the autopilot, though, was that it was designed for conventional controls you use in quadcopter drones. “We put an Arduino between the autopilot and the robot that translated autopilot commands to the morphing tail and wings’ motions of the robot,” Lentink says.
The Pigeon II passed the outdoor flying test. It could take off, land, and fly entirely on its own or with an operator issuing high-level commands like go up, go down, turn left, or turn right. Flight stabilization relied entirely on bird-like reflexes and worked well. But there was one thing electronics could not re-create: their robots used real pigeon feathers. “We used them because with current technology it is impossible to create structures that are as lightweight, as stiff, and as complex at the same time,” Lentink says.
Feathery marvels
Birds’ feathers appear simple, but they really are extremely advanced pieces of aerospace hardware. Their complexity starts with nanoscale features. “Feathers have 10-micron 3D hooks on their surface that prevent them from going too far apart. It is the only one-sided Velcro system in the world. This is something that has never been engineered, and there is nothing like this elsewhere in nature,” Lentink says. Those nanoscale hooks, when locked in, can bear loads reaching up to 20 grams.
Then there are macroscale properties. Feathers are not like aluminum structures that have one bending stiffness, one torque stiffness, and that’s it. “They are very stiff in one direction and very soft in another direction, but not soft in a weak way—they can bear significant loads,” Lentink says.
His team attempted to make artificial feathers with carbon fiber, but they couldn’t create anything as lightweight as a real feather. “I don’t know of any 3D printer that could start with 10-micron nanoscale features and work all the way up to macro-scale structures that can be 20 centimeters long,” Lentink says. His team also discovered that pigeon’s feathers could filter out a lot of turbulence perturbations on their own. “It wasn’t just the form of the wing,” Lentink claims.
Lentink estimates that a research program aimed at developing aerospace materials even remotely comparable to feathers could take up to 20 years. But does this mean his whole concept of using reflex-based controllers to solve rudderless flight hangs solely on successfully reverse-engineering a pigeon’s feather? Not really.
Pigeon bombers?
The team thinks it could be possible to build airplanes that emulate the way birds stabilize rudderless flight using readily available materials. “Based on our experiments, we know what wing and tail shapes are needed and how to control them. And we can see if we can create the same effect in a more conventional way with the same types of forces and moments,” Lentink says. He suspects that developing entirely new materials with feather-like properties would only become necessary if the conventional approach bumps into some insurmountable roadblocks and fails.
“In aerospace engineering, you’ve got to try things out. But now we know it is worth doing,” Lentink claims. And he says military aviation ought to be the first to attempt it because the risk is more tolerable there. “New technologies are often first tried in the military, and we want to be transparent about it,” he says. Implementing bird-like rudderless flight stabilization in passenger airliners, which are usually designed in a very conservative fashion, would take a lot more research, “It may take easily take 15 years or more before this technology is ready to such level that we’d have passengers fly with it,” Lentink claims.
Still, he says there is still much we can learn from studying birds. “We know less about bird’s flight than most people think we know. There is a gap between what airplanes can do and what birds can do. I am trying to bridge this gap by better understanding how birds fly,” Lentink adds.
Jacek Krywko is a freelance science and technology writer who covers space exploration, artificial intelligence research, computer science, and all sorts of engineering wizardry.
So, in all, Missouri’s case count in the H5N1 outbreak will stay at one for now, and there remains no evidence of human-to-human transmission. Though both the household contact and the index case had evidence of an exposure, their identical blood test results and simultaneous symptom development suggest that they were exposed at the same time by a single source—what that source was, we may never know.
California and Washington
While the virus seems to have hit a dead end in Missouri, it’s still running rampant in California. Since state officials announced the first dairy herd infections at the end of August, the state has now tallied 137 infected herds and at least 13 infected dairy farm workers. California, the country’s largest dairy producer, now has the most herd infections and human cases in the outbreak, which was first confirmed in March.
In the briefing Thursday, officials announced another front in the bird flu fight. A chicken farm in Washington state with about 800,000 birds became infected with a different strain of H5 bird flu than the one circulating among dairy farms. This strain likely came from wild birds. While the chickens on the infected farms were being culled, the virus spread to farmworkers. So far, two workers have been confirmed to be infected, and five others are presumed to be positive.
As of publication time, at least 31 humans have been confirmed infected with H5 bird flu this year.
With the spread of bird flu in dairies and the fall bird migration underway, the virus will continue to have opportunities to jump to mammals and gain access to people. Officials have also expressed anxiety as seasonal flu ramps up, given influenza’s penchant for swapping genetic fragments to generate new viral combinations. The reassortment and exposure to humans increases the risk of the virus adapting to spread from human to human and spark an outbreak.
With all the technological advances humans have made, it may seem like we’ve lost touch with nature—but not all of us have. People in some parts of Africa use a guide more effective than any GPS system when it comes to finding beeswax and honey. This is not a gizmo, but a bird.
The Greater Honeyguide (highly appropriate name), Indicator indicator (even more appropriate scientific name), knows where all the beehives are because it eats beeswax. The Hadza people of Tanzania and Yao people of Mozambique realized this long ago. Hadza and Yao honey hunters have formed a unique relationship with this bird species by making distinct calls, and the honeyguide reciprocates with its own calls, leading them to a hive.
Because the Hadza and Yao calls differ, zoologist Claire Spottiswoode of the University of Cambridge and anthropologist Brian Wood of UCLA wanted to find out if the birds respond generically to human calls, or are attuned to their local humans. They found that the birds are much more likely to respond to a local call, meaning that they have learned to recognize that call.
Come on, get that honey
To see which sound the birds were most likely to respond to, Spottiswoode and Wood played three recordings, starting with the local call. The Yao honeyguide call is what the researchers describe as “a loud trill followed by a grunt (‘brrrr-hm’) while the Hadza call is more of “a melodic whistle,” as they say in a study recently published in Science. The second recording they would play was the foreign call, which would be the Yao call in Hadza territory and vice versa.
The third recording was an unrelated human sound meant to test whether the human voice alone was enough for a honeyguide to follow. Because Hadza and Yao voices sound similar, the researchers would alternate among recordings of honey hunters speaking words such as their names.
So which sounds were the most effective cues for honeyguides to partner with humans? In Tanzania, local Hadza calls were three times more likely to initiate a partnership with a honeyguide than Yao calls or human voices. Local Yao calls were also the most successful in Mozambique, where, in comparison to Hadza calls and human voices, they were twice as likely to elicit a response that would lead to a cooperative effort to search for a beehive. Though honeyguides did sometimes respond to the other sounds, and were often willing to cooperate when hearing them, it became clear that the birds in each region had learned a local cultural tradition that had become just as much a part of their lives as those of the humans who began it.
Now you’re speaking my language
There is a reason that honey hunters in both the Hadza and Yao tribes told Wood and Spottiswoode that they have never changed their calls and will never change them. If they did, they’d be unlikely to gather nearly as much honey.
How did this interspecies communication evolve? Other African cultures besides the Hadza and Yao have their own calls to summon a honeyguide. Why do the types of calls differ? The researchers do not think these calls came about randomly.
Both the Hadza and Yao people have their own unique languages, and sounds from them may have been incorporated into their calls. But there is more to it than that. The Hadza often hunt animals when hunting for honey. Therefore, the Hadza don’t want their calls to be recognized as human, or else the prey they are after might sense a threat and flee. This may be why they use whistles to communicate with honeyguides—by sounding like birds, they can both attract the honeyguides and stalk prey without being detected.
In contrast, the Yao do not hunt mammals, relying mostly on agriculture and fishing for food. This, along with the fact that they try to avoid potentially dangerous creatures such as lions, rhinos, and elephants, and can explain why they use recognizably human vocalizations to call honeyguides. Human voices may scare these animals away, so Yao honey hunters can safely seek honey with their honeyguide partners. These findings show that cultural diversity has had a significant influence on calls to honeyguides.
While animals might not literally speak our language, the honeyguide is just one of many species that has its own way of communicating with us. They can even learn our cultural traditions.
“Cultural traditions of consistent behavior are widespread in non-human animals and could plausibly mediate other forms of interspecies cooperation,” the researchers said in the same study.
Honeyguides start guiding humans as soon as they begin to fly, and this knack, combined with learning to answer traditional calls and collaborate with honey hunters, works well for both human and bird. Maybe they are (in a way) speaking our language.
Enlarge/ Sure, they can use tools, but do they know where the nearest subway stop is?
“A thirsty crow wanted water from a pitcher, so he filled it with pebbles to raise the water level to drink,” summarizes a famous Aesop Fable. While this tale is thousands of years old, animal behaviorists still use this challenge to study corvids (which include crows, ravens, jays, and magpies) and their use of tools. In a recent Nature Communications study, researchers from a collaboration of universities across Washington, Florida, and Utah used radioactive tracers within the brains of several American crows to see which parts of their brains were active when they used stones to obtain food from the bottom of a water-filled tube.
Their results indicate that the motor learning and tactile control centers were activated in the brains of the more proficient crows, while the sensory and higher-order processing centers lit up in the brains of less proficient crows. These results suggest that competence with tools is linked to certain memories and muscle control, which the researchers claimed is similar to a ski jumper visualizing the course before jumping.
The researchers also found that out of their avian test subjects, female crows were especially proficient at tool usage, succeeding in the challenge quickly. “[A] follow-up question is whether female crows actually have more need for creative thinking relative to male crows,” elaborates Loma Pendergraft, the study’s first author and a graduate student at the University of Washington, who wants to understand if the caregiving and less dominant role of female crows gives them a higher capacity for tool use.
While only two species of crow (the New Caledonian crow and the Hawaiian crow) inherently use twigs and sticks as foraging tools, this study also suggests that other crow species, like the American crow, have the neural flexibility to learn to use tools.
A less invasive look at bird brains
Due to their unique behaviors, complex social structures, and reported intelligence, crows have fascinated animal behavioralists for decades. Scientists can study crows’ brains in real time by using 18F-fluorodeoxyglucose (FDG), a radioactive tracer, which the researchers injected into the crows’ brains. They then use positron emission tomography (PET) scans to see which brain areas are activated during different tasks.
“FDG-PET is a method we use to remotely examine activity throughout the entire brain without needing to do any surgeries or implants,” explained Pendergraft. “It’s like [a functional] MRI.” The FDG-PET method is non-invasive, as the crows aren’t required to sit still, which minimizes the stress the crows feel during the experiment. In the Nature Communications study, Pendergraft and his team ensured the crows were anesthetized before scanning them.
FDG is also used in various medical imaging techniques, such as diagnosing Alzheimer’s disease or screening for cancerous tissue. “Basically, the body treats it as glucose, a substance needed for cells to stay alive,” Pendergraft added. “If a body part is working harder than normal, it’s going to need extra glucose to power the additional activity. This means we can measure relative FDG concentrations within the brain as a proxy for relative brain activity.”
