Tag Archives: #birds

Researchers Shed Light On The Mechanism Of Magnetic Sensing in Birds (Biology)

Humans perceive the world around them with five senses – vision, hearing, taste, smell and touch. Many other animals are also able to sense the Earth’s magnetic field. For some time, a collaboration of biologists, chemists and physicists centred at the Universities of Oldenburg (Germany) and Oxford (UK) have been gathering evidence suggesting that the magnetic sense of migratory birds such as European robins is based on a specific light-sensitive protein in the eye. In the current edition of the journal Nature, this team demonstrate that the protein cryptochrome 4, found in birds’ retinas, is sensitive to magnetic fields and could well be the long-sought magnetic sensor.

First author Jingjing Xu, a doctoral student in Henrik Mouritsen’s research group in Oldenburg, took a decisive step toward this success. After extracting the genetic code for the potentially magnetically sensitive cryptochrome 4 in night-migratory European robins, she was able, for the first time, to produce this photoactive molecule in large quantities using bacterial cell cultures. Christiane Timmel’s and Stuart Mackenzie’s groups in Oxford then used a wide range of magnetic resonance and novel optical spectroscopy techniques to study the protein and demonstrate its pronounced sensitivity to magnetic fields.

The team also deciphered the mechanism by which this sensitivity arises – another important advance. “Electrons that can move within the molecule after blue-light activation play a crucial role”, explains Mouritsen. Proteins like cryptochrome consist of chains of amino acids: robin cryptochrome 4 has 527 of them. Oxford’s Peter Hore and Oldenburg physicist Ilia Solov’yov performed quantum mechanical calculations supporting the idea that four of the 527 – known as tryptophans – are essential for the magnetic properties of the molecule. According to their calculations, electrons hop from one tryptophan to the next generating so-called radical pairs which are magnetically sensitive. To prove this experimentally, the team from Oldenburg produced slightly modified versions of the robin cryptochrome, in which each of the tryptophans in turn was replaced by a different amino acid to block the movement of electrons.

Using these modified proteins, the Oxford chemistry groups were able to demonstrate experimentally that electrons move within the cryptochrome as predicted in the calculations – and that the generated radical pairs are essential to explain the observed magnetic field effects.

The Oldenburg team also expressed cryptochrome 4 from chickens and pigeons. When studied in Oxford, the proteins of these species, which do not migrate, exhibit similar photochemistry to that of the migratory robin, but appear markedly less magnetically sensitive.

“We think these results are very important because they show for the first time that a molecule from the visual apparatus of a migratory bird is sensitive to magnetic fields” says Mouritsen. But, he adds, this is not definitive proof that cryptochrome 4 is the magnetic sensor the team is looking for. In all experiments, the researchers examined isolated proteins in the laboratory. The magnetic fields used were also stronger than the Earth’s magnetic field. “It therefore still needs to be shown that this is happening in the eyes of birds” Mouritsen stresses. Such studies are not yet technically possible.

However, the authors think the proteins involved could be significantly more sensitive in their native environment. In cells in the retina, the proteins are probably fixed and aligned, increasing their sensitivity to the direction of the magnetic field. Moreover, they are also likely to be associated with other proteins that could amplify the sensory signals. The team is currently searching for these as yet unknown interaction partners.

Hore says “if we can prove that cryptochrome 4 is the magnetic sensor we will have demonstrated a fundamentally quantum mechanism that makes animals sensitive to environmental stimuli a million times weaker than previously thought possible”.

The cooperation between Oldenburg and Oxford is funded by a 6-year Synergy Grant from the European Research Council (ERC) with the title ‘QuantumBirds’. The collaboration is also a key part of the Collaborative Research Center, ‘Magnetoreception and Navigation in Vertebrates’ (SFB 1372) funded by the German Research Foundation (DFG), and Ilia Solov’yov is a Lichtenberg Professor funded by the Volkswagen Stiftung.

Featured image: Migratory birds such as European robins can sense the Earth’s magnetic field. Now researchers show for the first time that a molecule from their visual apparatus is sensitive to magnetic field. © Corinna Langebrake and Ilia Solov’yov


Reference: Xu, J., Jarocha, L.E., Zollitsch, T. et al. Magnetic sensitivity of cryptochrome 4 from a migratory songbird. Nature 594, 535–540 (2021). https://doi.org/10.1038/s41586-021-03618-9


Provided by University of Oldenburg

Previously Unknown Letter Reveals Einstein’s Thinking On Bees, Birds and Physics (Physics)

A recently discovered letter written by Albert Einstein discusses a link between physics and biology, seven decades before evidence emerges.

The 1949 letter by the physicist and Nobel laureate discusses bees, birds and whether new physics principles could come from studying animal senses.

It’s a position still being realised within physics to this day, with a growing body of research and understanding of how animals such as birds and bees find their way around.

Now a study led by RMIT University in Melbourne, Australia, discusses how recent discoveries in migratory birds back up Einstein’s thinking 72 years ago.

The previously unpublished letter was shared with researchers by Judith Davys – Einstein had addressed it to her late husband, radar researcher Glyn Davys.

RMIT’s Associate Professor Adrian Dyer has published significant studies into bees and is the lead author of the new paper on Einstein’s letter, published in the Journal of Comparative Physiology A.

Dyer said the letter shows how Einstein envisaged new discoveries could come from studying animals.

“Seven decades after Einstein proposed new physics might come from animal sensory perception, we’re seeing discoveries that push our understanding about navigation and the fundamental principles of physics,” he said.

The letter also proves Einstein met with Nobel laurate Karl von Frisch, who was a leading bee and animal sensory researcher.

In April 1949, von Frisch presented his research on how honeybees navigate more effectively using the polarisation patterns of light scattered from the sky.

The day after Einstein attended von Frisch’s lecture, the two researchers shared a private meeting.

Although this meeting wasn’t formally documented, the recently discovered letter from Einstein provides insight into what they might have talked about.

“It is thinkable that the investigation of the behaviour of migratory birds and carrier pigeons may someday lead to the understanding of some physical process which is not yet known,” Einstein wrote.

Professor Andrew Greentree, a theoretical physicist at RMIT, said Einstein also suggested that for bees to extend our knowledge of physics, new types of behaviour would need to be observed.

“Remarkably, it is clear through his writing that Einstein envisaged new discoveries could come from studying animals’ behaviours,” Greentree said.

More than 70 years since Einstein sent his letter, research is revealing the secrets of how migratory birds navigate while flying thousands of kilometres to arrive at a precise destination.

In 2008, research on thrushes fitted with radio transmitters showed, for the first time, that these birds use a form of magnetic compass as their primary orientation guide during flight.

One theory for the origin of magnetic sense in birds is the use of quantum randomness and entanglement. Both of these physics concepts were first proposed by Einstein.

The letter to Glyn Davys shows the openness of Einstein’s mind to novel possibilities observed in nature and the evidence that he took an interest in von Frish and his bee research.

‘Einstein, von Frisch and the honeybee: a historical letter comes to light’, with Adrian Dyer, Andrew Greentree, Jair Garcia, Elinya Dyer, Scarlett Howard and Fredrich Barth, is published in the Journal of Comparative Physiology A (DOI: 10.1007/s00359-021-01490-6).

Featured image: Letter by Albert Einstein, validated by The Hebrew University of Jerusalem, where Einstein bequeathed his notes, letters and records. © Dyer et al. 2021, J Comp Physiol A / The Hebrew University of Jerusalem


Provided by RMIT University

Birds Blood Functions As Heating System in Winter (Ornithology / Biology)

Researchers at Lund University in Sweden have discovered that bird blood produces more heat in winter, when it is colder, than in autumn. The study is published in the FASEB Journal.

The secret lies in the energy factories of cells, the mitochondria. Mammals have no mitochondria in their red blood cells, but birds do, and according to the research team from Lund and Glasgow this means that the blood can function as a central heating system when it is cold.

“In winter, the mitochondria seem to prioritize producing more heat instead of more energy. The blood becomes a type of radiator that they can turn up when it gets colder”, says Andreas Nord, researcher in evolutionary ecology at Lund University who led the study.

Until now, the common perception has been that birds keep warm by shivering with their large pectoral muscles and fluffing up their feathers. Less is known about other heat-regulating processes inside birds.

To investigate the function of mitochondria, the researchers examined great tits, coal tits and blue tits on two different occasions: early autumn and late winter. The researchers took blood samples from the birds and isolated the red blood cells. By using a so-called cell respirometer, a highly sensitive instrument that can measure how much oxygen the mitochondria consume, the researchers were able to calculate how much of the oxygen consumption was spent on producing energy and how much was spent on creating heat. Finally, they also measured the amount of mitochondria in each blood sample.

Blue tit (Photo: Johan Nilsson)

The results show that the blood samples taken in winter contained more mitochondria and that the mitochondria worked harder. However, the work was not to produce more energy, something the researchers had assumed since birds have a much higher metabolism in winter.

“We had no idea that the birds could regulate their blood as a heating system in this way, so we were surprised”, says Andreas Nord.

The researchers will now investigate whether cold weather is the whole explanation for the birds’ blood producing more heat in winter. Among other things, they will study whether the food that the birds eat in winter affects the mitochondria.

Featured image: Coal tit (Photo: Andreas Nord)


Publication:

Link to the article in The FASEB Journal:

Avian red blood cell mitochondria produce more heat in winter than in autumn


Provided by Lund University

To Figure Out How Dinosaurs Walked, Start With How They Didn’t (Paleontology)

By analyzing limb poses from modern birds and alligators with innovative 3D imaging technology developed at Brown, scientists have developed a better way to infer how extinct animals might have moved from place to place.

Paleontologists have made great strides in understanding how extinct animals like dinosaurs walked, ran, swam and flew when they were alive — but much about the mechanics of how different species moved remains uncertain. A new study led by researchers at Brown University offers a new perspective on this long-standing conundrum. 

The research, published on Monday, Feb. 8, inProceedings of the National Academy of Sciences, used an innovative 3D imaging technology developed at Brown called X-ray Reconstruction of Moving Morphology — or XROMM — to develop a method that could unlock new insights into how dinosaurs and other animals moved.

“By combining the latest technology for studying joint motion with unprecedented amounts of joint pose data, we’ve uncovered surprising new information that will improve reconstructions of locomotion in extinct animals,” said Armita Manafzadeh, a Ph.D. candidate in ecology and evolutionary biology at Brown and lead author of the research. 

And improving the ability for scientists to study animal biomechanics is important, Manafzadeh says, because knowledge of how individual species moved can be used to advance understanding of major evolutionary transitions and transformations, “like how animals with backbones came out of the water and started walking on land, how they went from walking on four legs to two, and how flight evolved.”

Traditional methods for studying how extinct animals walked rely on process of elimination. Fossil bones are fit together and manipulated to determine a joint’s mobility — all of the poses that can be assumed without the bones bumping into each other or coming apart. But because that approach only rules out how joints couldn’t have moved, scientists must then turn to other data sources — musculoskeletal models, trackway measurements, robotic simulations — to figure out how an animal’s joints realistically moved in life. In short, the approach has its limitations.

To determine whether joint mobility data might actually be more informative than paleontologists have tended to assume, Manafzadeh worked with two colleagues: Stephen M. Gatesy, a Brown professor of biology and co-director of the XROMM Technology Development Project; and Robert Kambic, who earned his Ph.D. from Brown as a student in Gatesy’s lab and is now at the Center for Movement Studies at the Kennedy Krieger Institute and the department of neuroscience at Johns Hopkins University School of Medicine.

Using XROMM’s 3D imaging technology, the researchers designed a study involving two living animals, the helmeted guineafowl and the American alligator, that are closely related to extinct dinosaurs. The researchers captured X-ray videos of the animals walking and having their limbs manipulated, took CT scans of the skeletons, and then used XROMM to measure nearly 600,000 joint poses. The researchers plotted these poses on three-dimensional joint mobility maps. 

Manafzadeh and her colleagues were excited to find consistent patterns that relate joint mobility to the specific poses used during locomotion in birds and alligators. These patterns, they say, can be applied to more accurately reconstruct the walking and running cycles of animals that no longer roam the earth.

“Thanks to these pose usage patterns, it turns out that what dinosaurs couldn’t do with their joints will give us some big clues about how they walked,” Manafzadeh said. “What’s more, this information has been right in front of us, hidden within the data that paleontologists are already collecting. We just didn’t know how to appreciate it yet.” 

The researchers say that their confidence in the patterns is supported by the hundreds of thousands of joint poses they’ve been able to measure and analyze. “We can now pursue future research to ask how broad those patterns are, how they evolved and why,” Gatesy said.

They also hope that future studies will adopt their new approach to help determine whether similar movement constraints can be applied to other extinct animals, like early mammals; other joints, like forelimbs; and other modes of locomotion, like flying.

“We’ve given our colleagues the tools to improve their reconstructions of extinct animals, and to test whether their existing hypotheses about locomotion fall into the patterns we find,” Manafzadeh said. “But our next big goal is to figure out why these patterns exist.”

This work was supported by the National Science Foundation, the Bushnell Research and Education Fund, a Sigma Xi Grant-in-Aid of Research, the Society of Vertebrate Paleontology Cohen Award for Student Research, an Association for Women Geoscientists/Paleontological Society Winifred Goldring Award, and a Brown University Presidential Fellowship.

Featured image: From here to there: The researchers used XROMM 3D imaging technology to measure the joint poses that birds (top) and alligators (bottom) use during walking to infer how the creature’s ancestors might have walked.


Reference: Armita R. Manafzadeh, Robert E. Kambic, Stephen M. Gatesy, “A new role for joint mobility in reconstructing vertebrate locomotor evolution”, PNAS February 16, 2021 118 (7) e2023513118; https://doi.org/10.1073/pnas.2023513118


Provided by Brown University

Noise and Light Pollution Alter Bird Mating Behavior (Ornithology / Biology)

It’s not only climate change impacting bird reproduction.

Some bird species change their reproductive behaviours in response to noise and light pollution, according to a study published in the journal Nature. The findings raise new questions about how responses to sensory stimuli, like noise and light, interact with other global changes, like a warming climate. 

An international team of researchers, including Hokkaido University ecologist Masayuki Senzaki, wanted to develop a better understanding of the effects of human-made noise and light pollution on reproductive success in birds. Scientific understanding in this area is currently limited to a few species at the local scale. The team used citizen-gathered records between 2000 and 2014 on more than 58,500 nests belonging to 142 bird species across the United States and assessed how this information was associated with high-resolution noise and light data from the nesting areas.

The scientists found that reproductive behaviours in bird species living in more closed woodland habitats were more significantly impacted by noise and light pollution compared to bird species living in more open grasslands and wetlands.

Specifically, light pollution was associated with earlier egg laying in both open and closed habitat species. Also, closed habitat species living in well-lit areas produced 16% larger egg clutches than those living in darker areas. The scientists think this is due to longer foraging times available to birds in well-lit areas.

Distribution map of artificial noise in the United States. The shade of color indicates the magnitude of noise. The points in the figure are the positions of the bird nests used in the analysis. Red indicates a nest that failed to breed, and black indicates a nest that succeeded in breeding (Masayuki Senzaki, et al. Nature. November 11, 2020).

Closed habitat species were negatively impacted by noise pollution, with evidence of reduced clutch sizes, increased hatching failure and fewer offspring capable of flight.

Further analyses at the species level showed that birds with low frequency birdsong were more negatively affected by noise pollution than those with higher frequency vocals. Notably, many closed habitat species chirp in low frequencies. The scientists believe that noise pollution masks these lower frequencies, interfering with male stimulation of females and thus their receptivity to breeding.

Also, species that see well in low-lit conditions laid eggs earlier in response to light pollution. The scientists expected they would have less nesting success compared to birds who do not see as well in low-lit conditions, due to a mismatch between peak food availability and food need. Instead, they found the birds had better nesting success. The scientists think this is due to their ability to successfully track available resources as climate temperatures rise. 

“There is widespread consensus that climate change is causing temperate birds to reproduce earlier,” says Senzaki. “But our data is showing that the impacts usually attributed to temperature could be overestimated, due to being confounded by the impacts of light pollution. Similarly, delays in the onset of bird breeding due to exposure to noise pollution could be leading to the underestimation of the impacts of climate change.” The team recommends data re-evaluations to understand how the different elements of global change interact to impact bird reproduction behaviours worldwide.

Funding: This work was supported by the US National Science Foundation (NSF; 1414171, 1556177, 1556192, 1812280), the NASA Ecological Forecasting Grant (NNX17AG36G), and the Japan Society for the Promotion of Science (JSPS) KAKENHI (17J00646).

Featured image: Fledgling chicks of the Pacific-slope flycatcher, whose breeding success rate was reduced due to noise (Photo: Masayuki Senzaki).


Reference: Masayuki Senzaki, et al. Sensory pollutants alter bird phenology and fitness across a continent. Nature. November 11, 2020. DOI: 10.1038/s41586-020-2903-7


Provided by Hokkaido University

Forming Sound Memories: Autism Gene Plays Key Aspect in Birdsong (Ornithology / Biology)

Inactivating gene prevents birds from learning fathers’ songs, could shed light on speech development in humans

Inactivating a gene in young songbirds that’s closely linked with autism spectrum disorder (ASD) prevents the birds from forming memories necessary to accurately reproduce their fathers’ songs, a new study led by UT Southwestern shows.

The findings, published online today in Science Advances, may help explain the deficits in speech and language that often accompany ASD and could eventually lead to new treatments specifically targeting this aspect of the disorder.

Todd Roberts, Ph.D. © UT Southwestern Medical Center

Study leader Todd Roberts, Ph.D., associate professor of neuroscience and a member of the Peter O’Donnell Jr. Brain Institute at UT Southwestern, explains that the vocalizations that comprise a central part of human communication are relatively unique among the animal world – not just for their complexity, but in the way they’re passed down from caregivers to offspring. Songbirds such as zebra finches also learn complex vocalizations from caregivers (songs are passed on to male offspring typically from their fathers). Much like humans, these animals have intricate brain circuitry devoted to this task, found in a region of the brain in the birds often referred to as the high vocal center, or HVC.

Because of the parallels between language learning in humans and song learning in the birds, Roberts says, songbirds are often used as a scientific model for understanding speech development in people, including conditions in which vocal communication is changed.

In their research, Roberts and his colleagues used zebra finches to study the role of a gene called FoxP1, one of the genes most correlated with ASD. Mutations of this gene cause a specific subtype of autism linked with severe language impairment and intellectual disability.

Unsuccessful Songbird Learning © UTSMC

Roberts, a Thomas O. Hicks Scholar in Medical Research, explains that learning vocalizations for both songbirds and humans consists of two different stages: First, birds and humans must form a memory of sounds. Next, they practice the sounds through imitation. Juvenile zebra finches typically practice their fathers’ song thousands of times a day over three months, rehearsing it around 100,000 times until it’s a close match. These birds can memorize the song 20 to 60 days after hatching, but they don’t start to practice singing it until approximately 35 to 40 days after hatching.

Genevieve Konopka, Ph.D. © UT Southwestern Medical Center

To better understand the role FoxP1 might play in both parts of this process, the researchers separated young zebra finches into two groups: Half the birds spent their early lives in contact with their singing fathers and continued to live with them while they practiced their songs; the other half spent their early lives with their songless mothers and later joined their fathers during the practice phase. Either before the birds formed memories of the songs or before they began practicing, Roberts and his colleagues used a technique called RNA interference to “knock down” FoxP1 in the birds’ HVC, ridding cells in this brain region of the vast majority of this gene’s protein products. This technique used constructs created in the lab of Roberts’ close collaborator and study co-author Genevieve Konopka, Ph.D., associate professor of neuroscience at UT Southwestern.

When the researchers analyzed the birds’ songs in adulthood, they found that only those with active FoxP1 during the song memorization phase were able to accurately reproduce their fathers’ songs. If this gene was knocked down during the practice phase, these birds could still correctly mimic the songs. However, birds in which FoxP1 was inactivated before memorization sang haphazard songs that bore no resemblance to the ones their fathers sang.

Successful songbird learning

“Our results suggest that FoxP1 is key for forming the song memories in these birds that are critical for imitation later in life,” Roberts says. “A similar deficit in humans could play a parallel role in speech development, blocking babies from forming memories of adult speech they hear around them and hindering their own communication as they grow.”

If this finding is reinforced in future studies, he adds, it could lead to new types of therapy for children with autism. Current ASD therapies centered on speech development often focus on helping children learn the motor skills necessary to produce sounds. However, Roberts says, techniques that focus on helping children form speech memories may be more important. In the future, he says, it may be possible to avoid speech deficits by replacing the missing FoxP1 protein using gene editing or altering FoxP1-regulated signaling using pharmaceuticals.

“This study is not only critical for understanding the symptoms of patients with FoxP1-related ASD but also lays the groundwork for studying many other genes associated with ASD using the songbird system,” adds Konopka, a Jon Heighten Scholar in Autism Research.

Other UT Southwestern researchers who contributed to this study include Francisco Garcia-Oscos, Therese Koch, Harshida Pancholi, Massimo Trusel, Vamsi Daliparthi, Fatma Ayhan, Marissa Co, Danyal H. Alam, and Jennifer E. Holdway.

This research was supported by grants from the National Institutes of Health  (R21DC016340, R01NS108424, R01DC014364, and R01MH102603) and the National Science Foundation (IOS-1457206).

Featured image: Studies involving the zebra finch, a songbird are helping researchers learn how the brain memorizes and learns songs ©UTSMC


Reference: Francisco Garcia-Oscos, Therese Koch, Harshida Pancholi, Massimo Trusel, Vamsi Daliparthi, Fatma Ayhan, Marissa Co, Danyal H. Alam, Jennifer E. Holdway, Genevieve Konopka, Todd F. Roberts, “Autism-linked gene FoxP1 selectively regulates the cultural transmission of learned vocalizations”, bioRxiv 2020.03.14.992016; doi: https://doi.org/10.1101/2020.03.14.992016


Provided by UT Southwestern Medical Center

Research Explains Why Crocodiles Have Changed so Little Since the Age of the Dinosaurs (Paleontology)

New research by scientists at the University of Bristol explains how a ‘stop-start’ pattern of evolution, governed by environmental change, could explain why crocodiles have changed so little since the age of the dinosaurs.

Crocodiles today look very similar to ones from the Jurassic period some 200 million years ago. There are also very few species alive today – just 25. Other animals such as lizards and birds have achieved a diversity of many thousands of species in the same amount of time or less.

Prehistory also saw types of crocodile we don’t see today, including giants as big as dinosaurs, plant-eaters, fast runners and serpentine forms that lived in the sea.

In the new research, published today in the journal Nature Communications Biology, the scientists explain how crocodiles follow a pattern of evolution known as ‘punctuated equilibrium’.

The rate of their evolution is generally slow, but occasionally they evolve more quickly because the environment has changed. In particular, this new research suggests that their evolution speeds up when the climate is warmer, and that their body size increases.

Lead author Dr Max Stockdale from the University of Bristol’s School of Geographical Sciences, said: “Our analysis used a machine learning algorithm to estimate rates of evolution. Evolutionary rate is the amount of change that has taken place over a given amount of time, which we can work out by comparing measurements from fossils and taking into account how old they are.

The crocodiles have had a much greater diversity of forms in the past. Examples include fast runners, digging and burrowing forms, herbivores, and ocean-going species © University of Bristol

“For our study we measured body size, which is important because it interacts with how fast animals grow, how much food they need, how big their populations are and how likely they are to become extinct.”

The findings show that the limited diversity of crocodiles and their apparent lack of evolution is a result of a slow evolutionary rate. It seems the crocodiles arrived at a body plan that was very efficient and versatile enough that they didn’t need to change it in order to survive.

This versatility could be one explanation why crocodiles survived the meteor impact at the end of the Cretaceous period, in which the dinosaurs perished. Crocodiles generally thrive better in warm conditions because they cannot control their body temperature and require warmth from the environment.

The climate during the age of dinosaurs was warmer than it is today, and that may explain why there were many more varieties of crocodile than we see now. Being able to draw energy from the sun means they do not need to eat as much as a warm-blooded animal like a bird or a mammal.

Dr Stockdale added: “It is fascinating to see how intricate a relationship exists between the earth and the living things we share it with. The crocodiles landed upon a lifestyle that was versatile enough to adapt to the enormous environmental changes that have taken place since the dinosaurs were around.”

The next step for the team’s research is to find out why some types of prehistoric crocodile died out, while others didn’t.

Reference: Stockdale, M.T., Benton, M.J. Environmental drivers of body size evolution in crocodile-line archosaurs. Commun Biol 4, 38 (2021). https://www.nature.com/articles/s42003-020-01561-5 https://doi.org/10.1038/s42003-020-01561-5

Provided by University of Bristol

Global Study on Bird Song Frequency (Ornithology / Biology)

Competition for mates leads to a deeper voice than expected based on size.

An analysis of the songs of most of the world’s passerine birds reveals that the frequency at which birds sing mostly depends on body size, but is also influenced by sexual selection. The new study from researchers of the Max Planck Institute for Ornithology and colleagues suggests that habitat characteristics do not affect song frequency, thereby refuting a long-standing theory.

A global study of songbirds like this field warbler shows that song frequencies primarily depend on body size. © Tomáš Albrecht

Many animals use acoustic signals for communication. These signals have evolved to maximize the effectiveness of the transmission and reception of the sounds, because this helps finding a mate or avoiding predation. One of the fundamental characteristics of acoustic signals is the frequency of the sound. In forested habitats, acoustic signals become attenuated because of sound absorption and scattering from foliage, which is particularly problematic for high-frequency sounds. Hence, a theory from the 1970s predicts that animals living in habitats with dense vegetation emit lower-frequency sounds compared to those living in open areas.

A team of researchers led by Bart Kempenaers from the Max Planck Institute for Ornithology in Seewiesen and Tomáš Albrecht from the Charles University in Praha and the Czech Academy of Sciences analysed the variation in song frequency of more than 5.000 passerine bird species, encompassing 85% of all passerines and half of all avian taxa. PhD student Peter Mikula collected song recordings primarily from xeno-canto, a citizen science repository of bird vocalizations, and from the Macaulay Library of the Cornell Lab of Ornithology.

Relationship between song frequency and body size

Contrary to a theory from the 1970s, habitat type does not affect song frequency, although in densely vegetated habitat, as here with the reed warbler, high frequencies tend to be attenuated. © Tomáš Albrecht

Contrary to the theory, the study reveals that the peak frequency of passerine song does not depend on habitat type. If anything, the data suggest that species living in densely vegetated habitats sing at lower frequencies, which is the opposite of what was predicted. As expected from basic physical principles, the researchers found a strong relationship between song frequency and body size and an effect of shared ancestry. “Both limit the range of sound frequencies an animal can produce”, says first author Peter Mikula. Heavier species sing at lower frequencies simply due to the larger vibratory structures of the vocal apparatus.

The study further reveals that species in which males are larger than females produce songs with lower frequencies than expected from their size. “This supports the hypothesis that the frequency of acoustic signals is affected by competition for access to mates”, says Bart Kempenaers. Song frequency may act as an indicator of an individual’s size and therefore of its dominance or fighting abilities. Thus, song frequency could influence reproductive success through competition with other males or even because it influences male attractiveness to females.

“Our results suggest that the global variation in passerine song frequency is mostly driven by natural and sexual selection causing evolutionary shifts in body size rather than by habitat-related selection on sound propagation”, summarizes Tomáš Albrecht.

References: Peter Mikula, Mihai Valcu, Henrik Brumm, Martin Bulla, Wolfgang Forstmeier, Tereza Petrusková, Bart Kempenaers & Tomáš Albrecht (2020)., “A global analysis of song frequency in passerines provides no support for the acoustic adaptation hypothesis but suggests a role for sexual selection”, Ecology Letters. https://onlinelibrary.wiley.com/doi/10.1111/ele.13662 https://dx.doi.org/10.1111/ele.13662

Provided by Max Planck Gesellschaft

Ringo Starr Of The Bird World Heading for Extinction (Ornithology / Biology)

New research from The Australian National University (ANU) shows palm cockatoos, renowned for their human-like musical drumming behaviour, are threatened with extinction.

According to co-author Professor Rob Heinsohn, the “animal kingdom’s match for Ringo Starr or Phil Collins” is facing rapidly declining population numbers.

“These shy and elusive birds, iconic to Cape York Peninsula in Far North Queensland, fashion thick drum sticks from branches, grip them with their feet and bang them rhythmically on the tree trunk, all the while displaying to females,” Professor Heinsohn said.

“Sadly, palm cockatoos have one of the slowest breeding rates of any bird, and our study shows the population is not producing enough young to replace the birds that die.”

The research used data from a long-term monitoring project together with new genetic information to work out how connected the scattered birds are on Cape York, and how well the good breeders compensate for those that fail to reproduce.

“Even best case scenarios show that the overall population will go down by more than a half in 49 years, the equivalent of three generations for the birds,” lead author Dr Miles Keighley said.

“This fast rate of decline means that the palm cockatoos qualify as ‘endangered’ under International Union for Conservation of Nature criteria.”

ANU researchers will work closely with the Queensland government to change the official conservation status of palm cockatoos.

“Long-lived birds like palm cockatoos, especially those that live in remote areas, are incredibly hard to study,” Professor Heinsohn said.

“We have worked very hard for over 20 years to understand the population trends. We used computer simulation techniques that allow us to look into the future – it’s a bit like having a crystal ball. But it only works if you have good data that tells you how the birds are tracking here and now.

“Palm cockatoos are very special birds. No other animal apart from humans fashions its own musical instrument, let alone creates its own rhythm.

“This only occurs among the palm cockatoos of Cape York Peninsula, adding extra impetus for protecting them and reversing the worrying downward trend.”

The research has been published in Biological Conservation.

References: Miles V. Keighley, Stephen Haslett, Christina N. Zdenek, Robert Heinsohn, “Slow breeding rates and low population connectivity indicate Australian palm cockatoos are in severe decline”, Biological Conservation, Volume 253, 2021, 108865, ISSN 0006-3207,
https://doi.org/10.1016/j.biocon.2020.108865.
http://www.sciencedirect.com/science/article/pii/S000632072030923X

Provided by Australian National University (ANU)