The Revelations of Animal Songs

Songs have power. That was never made clearer to me than when I recently read about some new discoveries involving the songs of animals. Songs can lead us to find rare wonders. They can engender a desire to explore tantalizing mysteries, and they can be the source for developing a sense of community with the other beings who share our planet.

For example, the love songs of Skywalker gibbons have alerted scientists to a new population of the endangered primates in Myanmar. Humpback whales sing louder when the wind is noisy, but don’t have the same reaction to the sound of boat engines. The songs of New Zealand’s smallest bird, the titipounamu (or rifleman), show that they may have a rudimentary version of the vocal learning ability we thought was possessed only by parrots, hummingbirds and songbirds.

And, as it turns out, our own songs have a lot in common with the songs of other animals.

Love songs lead to the location of an endangered species

Skywalker gibbon couples wake up each morning and sing to each other, their voices echoing across the forest canopy of their home. The primates’ endearing love songs have helped scientists confirm what was formerly a strong hunch: Myanmar has the largest population of endangered Skywalker gibbons on Earth.

When Star Wars-loving scientists identified Skywalker gibbons as a distinct species in 2017, fewer than 200 individuals were known to exist, all in southwestern China. Wanting to know just how many Skywalker gibbons might be out there, scientists from the University of California, Davis, and investigators from various Myanmar nongovernmental organizations, the Nature Conservation Society–Myanmar, and Fauna and Flora International–Myanmar conducted a population study.

Like their Jedi namesake, Skywalker gibbons cannot swim, so rivers tend to demarcate their boundaries. This led scientists to think Skywalkers likely extended into Myanmar between two rivers to the west and another to the east. So, from December 2021 to March 2023, a field team in Myanmar set up acoustic monitoring systems, listening each morning for the Skywalkers’ love songs, and recording the start and end times of the animals’ solos and duets.

The team then examined photographs for characteristics that distinguish Skywalker hoolock gibbons from other hoolock species. These include thinner eyebrows, a black or brown beard instead of a white one, and incomplete white face rings on the females. They also conducted threat assessment surveys in 12 villages to gather local knowledge about gibbons and the challenges they face. Using a noninvasive DNA sampling technique, they collected chewed fruits and plants from the gibbons. Genetic analysis of these samples confirmed the various species.

The scientists were able to genetically identify 44 new groups of Skywalker gibbons in Myanmar. Although, exact numbers of individuals are unknown, the Skywalkers were confirmed in areas previously thought to be occupied by eastern hoolock gibbons. Population estimates from 2013 suggested that there could have been up to 65,000 gibbons in the area where Skywalkers have now been identified, making this the largest probable population of Skywalker gibbons in one place.

This study, the results of which were published in the International Journal of Primatology in February 2024, is the first in the past century to confirm living Skywalker gibbons in Myanmar in two regions: Kachin State and as far south as Shan State. They reside in degraded forests—most of which are outside protected areas—and at much lower elevations than expected, showing that they’re highly adaptable. But scientists suspect that today’s actual numbers are lower than 65,000, given ongoing hunting and political unrest in Myanmar. They state that they hope that China and Myanmar will extend conservation efforts for Skywalker gibbons in this new geographic region and that their study will help guide updates for the International Union for Conservation of Nature (IUCN) Red List of Threatened Species.

Whale songs unmask more mysteries

For some time, we’ve known that whale songs are a means of communication. Now, a recent University of Queensland study has found that humpback whales sing louder when the wind is noisy but fail to do so when the sound of boat engines is nearby. It’s a surprising finding given that the frequency range of engine noise is similar to that of the wind. This discovery isn’t just a quirky factoid: it could have consequences for behavior and breeding.

Over millions of years, humpback whales have evolved with noise from natural sources, but noise from human-made vessels is still foreign to their instincts. Scientists say it’s possible that the whales are picking out differences other than frequencies, such as wind noise being broadband and the same over large areas, while vessel noise is generated by a single-point source with specific peaks in frequency.

The audio data for this study was collected in late 2010 off Peregian Beach in Queensland, Australia, during the whales’ southward migration from breeding grounds in the lagoon of the Great Barrier Reef to feeding grounds in Antarctica. Whale songs were recorded using an acoustic array of five hydrophone buoys, which sent signals back to the beach. A 62-foot fishing boat was introduced to produce vessel noise.

The researchers say that it might be that humpback whales are using other strategies to compensate for vessel noise, such as “spatial release from masking”—which is the ability to discriminate between audio signals coming from different directions—or “comodulation release from masking,” which is the ability to discriminate between noise and signal when the noise has distinctive frequency components and at least some of these components are not overlapping with the signal.

What’s not known is whether this lack of response to boat noise is making whales communicate less effectively or making breeding practices more difficult. Additional research will be needed because understanding humpback whales’ response to noise is important for developing mitigation policies for human activities at sea.

Birdsong highlights higher learning

Another study out of Australia, this time from the University of Auckland, is causing us to rethink how and when vocal learning evolved in birds.

Most animals communicate with unlearned, innate vocalizations; but some animals—such as bats, dolphins, elephants, humans and whales—are categorized as “vocal learners.” Scientists traditionally assumed that birds were split into two groups: those which can learn sounds (such as hummingbirds, parrots and songbirds) and those which can’t. But a study published in the scientific journal Communications Biology in May 2024 challenges that assumption.

Weighing about the same as six paper clips, titipounamu birds live in New Zealand’s high-altitude, mature, native forests, feeding on insects and making high-pitched sounds inaudible to some people. The bird is one of the country’s two surviving native wren species and a sort of evolutionary missing link between two of the most impressive learners, parrots and songbirds. Relics of Gondwana, the wrens likely existed in Aotearoa since before the islands broke away from the supercontinent, roughly 80 million years ago.

The researchers found that the local signatures of distantly related titipounamu birds had strong similarities if they lived near each other. But close relatives living far apart didn’t sound similar. That suggests that the birds’ songs may not be innate but learned from each other.

Scientists estimate that vocal learning in songbirds evolved 30 to 50 million years ago. But songbirds and parrots diverged long before that—closer to 80 million years ago. If New Zealand wrens are vocal learners, then it is likely that the common ancestor of parrots and songbirds was also capable of rudimentary learning; and in birds, this could have evolved millions of years earlier than previously thought.

To collect their data, the scientists closely monitored titipounamu nests at Boundary Stream Mainland Island in Hawke’s Bay, identifying and banding individuals. Then, over three summers, they recorded more than 6,800 feeding calls routinely made by adult birds that were bringing food to young nestlings. Detailed analysis of spectrograms of the calls—or voiceprints—revealed unique, individual vocal signatures. The researchers then acquired genetic information on the population at large.

Finally, the scientists used advanced genetic methods to estimate how much and which aspects of the vocal signatures came from genetics as opposed to the social environment (or vocal copying, where animals’ calls become acoustically similar). For some parameters, social environment was more important than genetics; and there were similarities with a known vocal learner, the zebra finch.

While the evidence isn’t conclusive, it is strongly suggestive of rudimentary vocal learning abilities; and scientists may need to stop classifying birds as either vocal learners or vocal nonlearners. What’s unraveling in this study is similar to humans’ ability to adjust our ways of speaking in different dialectic, hierarchical or social settings—modulating our voices to better fit in with certain social groups. This aptitude may be much more widespread and likely exists along a spectrum, conclude the researchers.

Syrinxes show similarities

While humans have long been fascinated by birdsong and bird sounds—from coos and honks to peeps and quacks—little is known about how the unique vocal organ of birds, the syrinx, varies from species to species or its deeper evolutionary origins.

A trio of recent studies led by researchers from The University of Texas at Austin is changing that. They include high-resolution, anatomical scans of syrinxes from hummingbirds and ostriches—the world’s smallest and largest birds—and the discovery that the syrinx and the larynx, the vocal organ of mammals and reptiles, including humans, share the same developmental programming.

This genetic connection between the vocal organs is an exciting, new example of “deep homology,” a term that describes how different organs or tissues can share a common genetic link. The research that resulted in the three studies got its start in 2013 when a paleontologist discovered a syrinx in a fossil of a duck-like bird that lived in what is now Antarctica during the Late Cretaceous Period. It’s the oldest syrinx to be discovered. But when she tried to compare the fossil syrinx to the syrinxes of modern birds, she found the scientific literature lacking.

This set her on a mission to modernize syrinx data collection. Over the years, she and members of her lab developed new methods for dissecting, preserving and CT-scanning syrinxes across many different groups of birds. These enhanced views of the hummingbird and ostrich vocal organ have shown that bird behavior may be just as important as the syrinx when it comes to the repertoire of sounds these birds produce.

For example, in the study of the ostrich syrinx, the researchers found no significant differences in syrinx anatomy between adult female and male birds (previous studies focused only on male ostriches). However, even though both females and males have the same vocal equipment, male ostriches tended to make a wider variety of sounds, which were often associated with aggressive behaviors among rowdy males. On a visit to a Texas ostrich farm, the researchers recorded 11 types of calls, ranging from high-frequency gurgles and peeps in baby ostriches to low-frequency boos and booms in adult males. These included a few call types that had never been recorded before. The only sounds definitively recorded from adult female ostriches were hisses. It seemed what the females lacked in range, they made up for in attitude.

For the hummingbird study, the researchers compared the bird’s syrinx to the syrinxes of nightjars and swifts, two close relatives. They found that all three birds have similar vocal folds in their syrinxes despite having different ways of learning their calls. Nightjars and swifts work with a limited repertoire of instinctive calls, while hummingbirds can elaborate on calls by learning complex songs from each other, an example of vocal learning.

Before the study, it was uncertain if swifts even had vocal folds. But the findings suggest that the common ancestor of all three birds also had a similar vocal-fold structure, and that it may have helped lay the groundwork for the evolution in vocal learning in hummingbirds.

At the same time that the paleontologist and her team were developing methods to preserve and capture syrinx anatomy across bird species, they were collaborating with a developmental biologist at Harvard University on investigating the evolutionary origins of the syrinx by tracking the gene expression that accompanied vocal organ development in the embryos of birds, mammals and reptiles. The study, published in the journal Current Biology, details how scientists discovered the deep connection between larynx and syrinx tissues by observing that the same genes were controlling the development of the vocal organs in mice and chicken embryos, respectively, even though the organs arose from different embryological layers. They form under the influence of the same genetic pathways, ultimately giving the vocal tissue similar cellular structure and vibratory properties in birds and mammals.

The study’s authors also analyzed syrinx development across 14 different bird species. They found that the common ancestor of modern birds probably had a syrinx with two sound sources, or two independently functioning vocal folds. This trait is found in songbirds today, allowing many to create two distinct sounds at the same time. This means that the common ancestor of birds may have been making similarly diverse calls.

These results shed light on the syrinx’s origins, but it’s still unknown when the syrinx first developed and whether nonavian dinosaurs—the ancestors of today’s birds—had the vocal organ. No one has yet found a fossil syrinx from a nonavian dinosaur. But the best way to understand the possibilities for ancient dinosaur sounds is to continue studying vocalization as it exists today in birds (the dinosaurs that are still with us) and other reptile cousins.

Universal songs connote our connectedness

Love songs, whale songs or birdsong—music, as ancient Greek philosopher Plato wrote, “gives soul to the universe, wings to the mind, flight to the imagination, and charm and gaiety to life and to everything.”

I believe that listening to the songs of all beings will lead us to a better understanding of and compassion for all who share this world. For as another writer—Danish author Hans Christian Andersen—once said, “Where words fail, music speaks.”

Here’s to finding your true places and natural habitats,

Candy