The sequence about hummingbirds in Flight: The Genius of Birds began with a demonstration of a new UAV (unmanned aerial vehicle) funded by DARPA, called the nano-hummingbird. Paul Nelson applauded the spectacular piece of engineering of this device that weighed less than an AA battery yet could hover, turn, and take pictures. Still, it was light-years behind its namesake, as he pointed out. The robot was not really autonomous; it needed a human to operate the controls, it flew only oriented vertically, and it could not lay eggs and reproduce itself. Still, for robotics, it was a big achievement. Popular Science said testing required 300 wing designs.
Attempts to replicate the flight of hummingbirds and insects have progressed since then. Purdue University proudly announced its latest contestant. Their robo-hummingbird is lighter, smaller, and uses artificial intelligence (AI) to move about with more autonomy. Xinyan Deng and her team spent years studying live hummingbirds.
Deng’s group and her collaborators studied hummingbirds themselves for multiple summers in Montana. They documented key hummingbird maneuvers, such as making a rapid 180-degree turn, and translated them to computer algorithms that the robot could learn from when hooked up to a simulation.
Further study on the physics of insects and hummingbirds allowed Purdue researchers to build robots smaller than hummingbirds — and even as small as insects — without compromising the way they fly. The smaller the size, the greater the wing flapping frequency, and the more efficiently they fly, Deng says. [Emphasis added.]
Small is good, but they haven’t yet been able to disconnect the wires to the device. Deng explains why you can’t scale down the popular drones found in stores:
Drones can’t be made infinitely smaller, due to the way conventional aerodynamics work. They wouldn’t be able to generate enough lift to support their weight.
But hummingbirds don’t use conventional aerodynamics — and their wings are resilient. “The physics is simply different; the aerodynamics is inherently unsteady, with high angles of attack and high lift. This makes it possible for smaller, flying animals to exist, and also possible for us to scale down flapping wing robots,” Deng said.
Using carbon-fiber wings that mimic the attack angles of hummingbirds, the Purdue team created one robotic hummingbird weighing only 12 grams, and an insect model weighing only 1 gram. They both create enough lift to carry more than their own weight. A video shows them operating in split-screen with a hummingbird:
Once humans master the art of lightweight, maneuverable flight, they might be able to use the devices for search and rescue, finding their way into crevices of collapsed buildings and learning the path as they go. Getting them to lay eggs and reproduce, though, is still light-years ahead.
A preprint (not yet peer reviewed) paper by Sahmorie Cameron and two others on bioRxiv adds to our understanding of sea turtle navigation.
Philopatry [tendency to remain in place] and long distance migrations are common in the animal kingdom, of which sea turtles are flagship examples. Recent studies have suggested sea turtles use the Earth’s magnetic field to navigate across ocean basins to return to their natal area; yet the mechanisms underlying this process remain unknown. If true, the genetic structure at nesting sites should positively correlate with differences in location-specific magnetic vectors within nesting regions. Here, we confirm this working hypothesis and demonstrate trans-species adaptation of sea turtles to local magnetic field vectors in certain nesting regions of the world, but not others. We describe magneto-sensing regions as characterized by sharp clines of total and vertical field intensity vectors offering the navigation cues that could increase philopatric accuracy and promote genetic structuring between sea turtle populations.
In other words, the genetics of a turtle population should correlate to the magnetic signature at the locations where they breed. Some locations have more ideal magnetic vectors.
Positive correlations between geomagnetic field vectors and population genetic structure would confirm that sea turtles use vectors of the earth magnetic field for their philopatric migration. Finding no such pattern would challenge the imprinting hypothesis of early life stages as a potential universal mechanism of navigation.
Examining mitochondrial genes from five of the seven sea turtle species in 144 locations, “this finding shows that geomagnetism is a basis acting as a navigational cue that underlies philopatric behaviours in sea turtle species at a time-scale relevant with both ecological (navigation) and evolutionary (population structure) processes.” The correlation held true — for most sites. It was not found at some sites. This may be due to weaknesses in the geomagnetic vectors at some points on the globe that render them insufficiently strong for navigation. Consequently, “geomagnetism-mediated philopatric behaviour is region-specific and not species-specific.” Only where the vertical field intensity is strongest will turtle populations congregate successfully. The fact that the magnetic pole drifts complicates matters. A strong cline (field line intensity) at a coastline may drift out to sea.
While our findings are consistent with previous studies, we demonstrate that geomagnetic imprinting is regional, not universal. This result concurs with secular variation of the Earth’s magnetic field, which causes female sea turtles to change natal locations as magnetic signatures drift along coastlines. In general, our result demonstrates that slight inaccuracy in the detection of the geomagnetic field vector may lead turtles to fail to return to breeding sites.
The populations that can successfully read the field at a coastline where it is strong, therefore, will tend to reflect their population genetic information within the group due to lower gene flow between individuals.
The correlation does not explain how turtles sense the field, or navigate by it. “Philopatry can be as accurate as 50 km and shapes population structure,” the authors say. “Yet, its underlying mechanisms remain unknown.” The magnetic sense surely must be exquisite, whatever it is, to work as well as it does. Females can return to their natal beach through murky ocean water from thousands of kilometers from where they emerged as hatchlings 25 to 30 years before. No one knows how other turtles and other long-distance navigators, like salmon, European eels and elephant seals do it.
As inspiration for engineering, butterflies remain favorites. Chemical & Engineering News reports the invention of a new sound sensor inspired by the nanostructures on the wings of morpho butterflies, those iridescent blue beauties. “3-D nanostructures in iridescent butterfly wings could be harnessed to make small, fast, and sensitive acoustic detectors,” they say. How do they work?
Materials scientists and engineers at Shanghai Jiao Tong University decided to take advantage of the unique photonic nanostructures on Morpho butterfly wings to sense the sound waves. Others have already used the wings or tried to mimic their structures to make gas and heat sensors and photocatalysts. Morpho wings are covered with rows of tile-like scales. Each scale has long parallel ridges that, in cross section, look like pine trees. Light waves bounce off these tree-like nanostructures and interfere to create shimmering colors; the colors and brightness change when the ridges deform under mechanical or chemical changes.
Acoustic waves can be focused by these photonic structures, too. Vibrations in the tree-like nanostructures can be picked up by photodetectors. The advantage is that this method avoids interference from other sources. “Because light waves interact with nanoscale structures and are immune to electromagnetic interference, optical acoustic sensors can be smaller and more sensitive and have a faster response time.”
Worries about monarch butterflies continue. In April, Anurag A. Agrawal wrote a Commentary in PNAS about “Advances in understanding the long-term population decline of monarch butterflies.”
Monarch butterflies are an icon of nature: spectacular in form, known for their unfathomable annual migration, and frequent visitors in our backyards… It is no wonder they are a darling among invertebrates. And what has now captured our attention is the striking and precipitous decline of monarch populations over the past two decades.
The all-time low of monarch visitation to the overwintering site in Mexico was in 2013. Although growing use of pesticides is the prime culprit, Agrawal notes that it may not be the only or primary cause of the problem. For one, populations far removed from each other, such as in California and Florida, show similar rates of decline. Is it due to deforestation, drought, climate change, or lack of nectar sources? Are predators increasing? Why are other species like birds and bats also declining in the same period? “Indeed,” he says, “additional data and statistical modeling are needed.”
Everyone who loves these one-gram wonders can agree with his passion: “Saving an iconic butterfly is important and would help us sustain beauty, wonder, and majesty in nature.”
Image: Hummingbird and hummingbird robot, from “Hummingbird Robots: Naturally Intriguing,” via Purdue University (screen shot).