Sounds Wild and Broken, page 34
I rented this small apartment in Paris for a few days, expecting nothing more than a convenient place to stay while I visited family. But the blackbird’s song woke one of my earliest memories. The whistled melody and the rich tone imparted by the courtyard unearthed a long-buried sensory remembrance, a fragment of childhood experience. Without my understanding why, the sound felt deeply familiar, in the same way that the aromas of foods from early youth can evoke memories of belonging. As a child, I lived in a similar apartment in Paris, but until this moment I had no conscious memory of any bird there. Later, my mother confirmed that, yes, a blackbird sang every spring from the courtyard and small roof garden behind our apartment on Rue Tiphaine. She said that for her, the blackbird’s song was a reminder of the richness of the dawn chorus of birds in the English countryside of her youth. The song was a welcome sign of spring but also melancholy in its aloneness, missing the dozens of other species that sing alongside the blackbird outside the city.
Nearly half a century had passed since I last heard a blackbird singing in a courtyard, but the melody and timbre of the sound somehow traveled with me all those years, held in the sparkle of electrical charges on the fatty membranes of my nerve cells. When the sound came to me again, years later, these energies woke and pushed feelings of delight and warmth into consciousness. Thank you, memory. Impressive.
Our human experience of long-term auditory memory sets us apart from our close relatives, the other primates, but likely not from other vocal learners like birds and whales. Nonhuman apes and monkeys have excellent memory for visual and tactile experience, but these powers seem not to extend to sound, especially in the long term. Humans, though, readily recall the nuances of sounds. Most of these memories are short-lived, but some can last a lifetime: The sound of a loved one’s voice. A melody from childhood or adolescence. The pronunciation and meanings of words, even those unused and unheard for decades. The soundscapes of city streets and backyards. The inflections and textures of the voices of other species. These dwell inside us, acting not as static archives but as living guides to the meanings of sensory experience, activating in an instant.
Our sonic memory differs from that of other primates because evolution has reshaped our brains to make us better participants in aural culture. Like many singing birds, human culture is transmitted by sound, as well as by sight and touch. But the cultures of monkeys and nonhuman apes are almost entirely visual and tactile. As a result, humans and birds have well-developed connections between the areas of the brain involved in the perception and comprehension of sound, links that are much weaker in other primates. Brain scans show that these neural pathways are required for long-term auditory memory. My decades-long memory of the blackbird was indirectly made possible by human language.
Aural memory, then, allows us to understand and navigate both the human and beyond-human worlds. The human talent for long-term memory of sound may have helped us as we explored new regions. Recall of both individual sounds and of the feel of soundscapes gave our ancestors points of reference through which to assess and understand new environments. In some cultures—notably among some aboriginal nations in Australia—human song becomes part of this geography of sound. Song lines meld human and beyond-human sound and stories into memories that travel through time across many generations. The computers that scientists use to analyze thousands of hours of digital sound in Borneo and elsewhere are an extension of an ancient human capacity for place reading through sound.
Listening to the blackbird’s voice bloom, I have a strong feeling that he is using the space to his advantage, like a human singer finding a favorable performance spot. Acquaintances tell me of blackbirds holding forth at the rim of courtyards in Berlin and London, creating stunning aural displays. Intention is hard to prove, though. Perhaps the birds perch at random throughout their territories, sometimes happening upon reverberant spaces. But such insensitivity seems unlikely for a bird whose energies are largely devoted to song for much of the year, starting in earnest in January, peaking in April and May, then declining through the summer and autumn. Surely, he is a connoisseur of the qualities of his voice in the world, listening, remembering, and adjusting just as he did as a youngster when he learned his song through attentive listening and studious refinement through practice?
Such improvisational and flexible use of the city accords with the rest of the bird’s biology. There are no records of free-living blackbirds in Paris before the 1850s, although some were kept as caged singing ornaments. The birds’ captors used whistles and hand-cranked miniature organs—devices called merlines for blackbirds and serinettes for finches such as canaries—to tutor the birds’ songs. Now blackbirds are common wherever trees are scattered among buildings or in the city’s many parks, large and small. The same is true across much of Western Europe. Before the nineteenth century, blackbirds were forest specialists, living only in wooded countryside. As they colonized cities, their voices, behavior, and physiology changed. The song that I remember from my childhood has within it the imprint of the city.
Urban colonization started in winter. A few adventurous nineteenth-century blackbirds lingered in the city instead of decamping to southern Europe and North Africa like most of their kind. These birds were likely drawn to both heat and food. The city is usually several degrees warmer than the countryside. Seeds and fruits in gardens and parks, along with spilled and discarded food from domestic animals and humans, increased the allure. Blackbirds were joined in this winter move to the city by other birds like greenfinches, blue tits, and mallards. These innovators thrived and soon started breeding within the city, abandoning their ancestral woodlands and marshes and becoming urban creatures. Birds on other continents have made similar adaptations to urban life, often breeding at higher densities in the city than in rural areas. House sparrows, European starlings, and rock pigeons are among the most widely distributed animals on the planet. They are joined by a wide taxonomic variety of other species, including lorikeets and ibises in Australia; night-herons and monk parakeets in North America; bulbuls and mynas in Asia; mousebirds, kites, and martins in Africa; and various crows and magpies worldwide.
In Paris, the blackbirds’ colonization of the city was helped by the construction of parks and wide, tree-lined avenues in the middle of the nineteenth century. Georges-Eugène Haussmann, at the direction of Napoleon III, razed much of Paris, transforming a tangle of narrow streets into an ordered web of grand boulevards, linked to parks and public squares. To accommodate the hundreds of thousands of displaced people and to provide a larger canvas for his work, Napoleon annexed surrounding towns in 1859 and 1860, expanding Paris to its present borders. The street where I heard the blackbird as a child, now in the fifteenth arrondissement, was a small independent town in the 1850s, between the marshes along the Seine and the wall and tollgate that defined the southern edge of the city. Likely no blackbirds sang in narrow streets that ran, without sidewalks or trees, between closely packed building facades. After Haussmann was finished with it, a tree-lined thoroughfare ran across its north edge, connecting small parks and apartment buildings, some with vegetated courtyards. The bird that I heard in the 1970s was likely a descendant, a century later, of avian colonists to this new Paris. Haussmann’s project, which turned the city center and surrounding towns into a modern urban space, paradoxically coincided with and facilitated the arrival of a bird that formerly sang only in the forest.
In cities, blackbirds sing higher, louder, and at a faster pace than in the countryside. This amped up vibe has many causes, each an adaptation to the new urban habitat.
Traffic noise is the most obvious acoustic difference between the city and its surrounds. Engines, tires on asphalt, and the throb of road construction erect a wall of mostly low-frequency noise. When I’m in the city, I usually don’t notice this background growl. My attention is drawn instead to the intermittent punches of sirens, horns, and shouts. But a microphone fed into a computer reveals what our minds usually filter out: in the city we swim, always, within a sea of low-pitched noise.
The rumble of cities is so pervasive that it penetrates a kilometer or more into the earth. When COVID-19 lockdowns slowed human movement and industry, geologists recorded a global stillness previously unknown to their seismic instruments. No doubt animals like elephants and whales that sense low-frequency ground- and waterborne sound waves also noticed the difference, although how this affected their behavior is so far unknown. Stillness also fell on the world of aerial sound, but unlike our close attention to potentially catastrophic tremors in rock, we lack a standardized international network of sound monitors in air. Across the world, people suddenly became far more aware of the voices of the beyond-human world. These species were always there, but their sounds were masked by noise and our inattention.
Deep sounds have long wavelengths and are thus able to flow around obstacles. The low-pitched throb of the city carries far. Even in streets away from busy roads, rail lines, or construction, low-frequency noise pervades the air. In forests or prairies, away from the city, the overall sound level is softer and is often dominated by a bump in the midfrequencies, the sounds of wind in trees or grasses.
The higher-pitched sounds of urban birds punch and leap over the wall of low noise. Loudness lets them push through the clamor, like a human shouting over the noise of an engine. By singing higher—usually an increase equivalent to one or two human musical notes—the birds use frequencies less masked by the din of traffic. These adaptations to the city are not just transpositions of the song to a higher register; the birds change the composition of their songs too, using more high-pitched elements. Blackbirds also shrink the lower, introductory part of their song relative to the later, higher trills. The city has left its mark within the vigor, frequency, and form of the birds’ songs.
For the white-crowned sparrows that I listened to in San Francisco, the background growl has increased over the last fifty years. This change has nudged their cultural evolution of song in new directions. Sparrows in noisy environments—whether near ocean surf or the roar of traffic—abandon the lower-pitched elements of their songs, either by dropping these syllables or by singing them higher. The ocean has always been present, but traffic noise has increased across the city, subjecting the sparrows in formerly quiet locales to higher levels of noise.
In the noisier parts of the Bay Area, sparrows now are shriller than those from the 1960s and 1970s. This change adapts them to the new soundscape, but the song is now, from a sparrow’s perspective, less impressive. By cutting off what was the low end of their songs, the birds have lost one of the ways they demonstrated their vigor, by producing songs that zipped rapidly from low to high and back again. To compensate, urban white-crowned sparrows have found other ways to advertise their performance capabilities, increasing the complexity of individual song elements, adding ornaments and accents.
When the COVID-19 pandemic shut down much of San Francisco’s traffic in the spring of 2020, background noise levels reverted to those of the 1950s. The sparrows responded by reverting to quieter and lower-pitched songs of a kind that had not been heard there in decades. We do not know whether these changes happened through the flexibility of individual birds or by cultural evolution as juveniles preferentially copied songs that worked well in the nearly car-free soundscape.
Experimental studies with randomized playbacks have confirmed that these responses to noise are not mere correlations. By blasting sounds of traffic or industry into some animal territories and not others, scientists have shown that birds assaulted with noise sing higher and louder. The effects start early. Even among nestlings, stress hormones are higher in noisy places. These youngsters raised in cacophony also have shorter telomeres, genetic markers of aging on chromosomes. Other species also feel the effects of noise. Reviews in 2016 and 2019 of more than two hundred scientific studies found that amphibians, reptiles, fish, mammals, arthropods, and molluscs were all affected. Noise variously affects feeding, movement, vocalization, and thus the fecundity and viability of animal populations. Excessive urban sounds can even interfere with other senses. Great tits find it harder to see camouflaged prey amid a din.
We intuitively understand these stories of noise. Our bodies have experienced the same. When a friend’s voice is swamped by the wave of engine sound from a passing bus or the sonic assault of a busy restaurant, we feel the masking power of unwanted sound. We respond either with silence, waiting out the surge, or by cranking up our voices. When we try to talk over the noise, we instinctively do so by speaking both louder and at a higher pitch. We, too, get loud and shrill in the city. We also elongate our vowels, shoving them through the obstruction, and change the timbre of our voices, favoring higher harmonics. All this happens without conscious awareness, a process guided by brain stems that listen to the surroundings and adjust our voices. The increase in vocal loudness in noise was first described by French otolaryngologist Étienne Lombard as he researched hearing loss. The Lombard effect, because it is unconscious, cannot be faked. Patients who, for legal reasons, were pretending to be deaf had their deceptions unmasked. When Lombard played loud sounds into their ears, these bilkers spoke more vigorously, their attempts to defraud employers and the government betrayed by their brain stems. It is not only our voices that change in noise. We also add more spice and salt to food in loud environments, perhaps in a bid to push other important senses through domineering sound.
The Lombard effect is present in vertebrate animals from fish to birds and mammals, although in some species it seems to have been lost. The effect allows short-term compensation and accommodation of noise, a complement to longer-term genetic, cultural, or physiological adaptations. Because the effect changes so many aspects of sound—pitch, amplitude, timbre, emphasis on different syllables—disentangling which of these actually benefits wild animals is challenging. The energetics and anatomy of sound production underlie many of these tangles. For example, as every human toddler knows, high-pitched sounds require less effort to bawl than lower tones. To hammer your parents’ ears: scream and squeal, don’t roar or rumble. Although these shrill cries will not travel as far as low sounds, they give impressive volume for minimal effort. The same is true for nonhuman animals in noise. Because loud low sounds take more energy to make than high calls, it is most efficient to yell at high frequencies. The higher tones of animal sound in noise may be a secondary consequence of the animals punching more energy into each utterance.
A study of Eurasian blackbirds in and around Vienna found that in the forest, songs carried for 150 meters or more. In the loudest parts of the city, the songs carried only 60 meters. A higher-pitched song could partly vault over the noise and boost this reach in the city to 66 meters. But an extra five decibels yielded more benefit, pushing the reach of the song to 90 meters. Five decibels is about the extra amplitude generated by songbirds in city noise. The primary adaptation of blackbirds to urban soundscapes, then, seems to be louder songs. The increased frequency emerges as a side effect of loudness, and as a bonus, gives an advantage by overcoming masking. The same is true for the changes in composition in the songs. City birds preferentially use high-amplitude elements of their songs, which also tend to be high-pitched.
It is not only noise that differs between city and the countryside. Urban blackbirds often live in denser populations, increasing the number of daily interactions with near neighbors. Their songs are partly a result of this changed social context. Even in the countryside, blackbirds with many close neighbors sing higher and faster. The city also seeps into the hormones of blackbirds. For unknown reasons, female blackbirds in cities lay eggs with fewer androgens such as testosterone than their forest-dwelling cousins. Adult male blackbirds have lower testosterone than birds in the countryside. City blackbirds also have higher levels of stress hormones, partly due to the burden of contamination with lead and cadmium in polluted cities, but their blood has a higher capacity to absorb and buffer chemical stress. Hormones are physiological stimuli for singing and social interaction, but exactly how they shape song and behavior in urban blackbirds is so far unknown.
Cities are like newly emerged volcanic islands in an ocean, akin to the earliest years of the Hawaiian or Galápagos Islands. Only a few species colonize these novel outposts. The islands are incubators of biological innovation: the new arrivals swiftly adapt, shaping their behaviors and bodies to the new world they have discovered. Eurasian blackbirds in Western European cities not only have songs different from their sylvan forebears, these urban birds also sing and forage at night under streetlights; breed three or more weeks earlier; tend not to migrate; have rounder wings well suited for short-distance flight and not migration; and have more cautious, neophobic personalities, yet they eat novel foods, feasting on seed at feeders, spilled human grain and rubbish, as well as enjoying exotic fruit on ornamental plants.
Although populations of urban blackbirds thrive, producing more than enough offspring in most years to sustain and even swell their numbers, individual birds bear a cost. Blackbirds age faster in the city than in rural forests, a decline revealed by their chromosomes. The ends of these chromosomes—the telomeres, markers of aging in animals from humans to birds—shorten rapidly in the city, perhaps because of the physiological stress of living under continual sensory and chemical bombardment. But predators and ticks are fewer in the city, as is the incidence of avian malaria, and so although urban blackbirds have ragged chromosomes, they often live longer than those in rural areas. They are perhaps like aged rock stars, their bodies ravaged by a loud, fast, and chemically sodden youth but persisting into a secure dotage.
