Have you ever heard a bird sing and wondered what species it was? Or how birds came to sing in the first place? Historically, birdsong has inspired scientific theories, human mimicry, and awe. The voice of another species seems full of secrets about the history of life on Earth, if only we can translate it. Practiced birders can detect which species of bird is present by voice alone—sometimes they’re even able to detect the crooner’s sex. When a study looking at how one species becomes two relied on the behavior pattern of only males singing, I began to wonder if universally, only male birds sang. As I pursued this question, I discovered how juxtapositions of animal behavior and human society can produce both novel ideas and reinforce stubborn biases.
Evolution Mediated by Song
In February of 2015, I attended a lecture by the renowned evolutionary biologists, Rosemary and Peter Grant. The Grants, who famously witnessed evolution occur within their lifetimes, spent 40 years contemplating speciation. Beginning in 1973, they lived for six months of each year on Daphne Major, a 4.9 square kilometer island in the Galapagos, and became familiar with all aspects of the island’s ecology. Focusing on Darwin’s Finches, their research tracked changes in the birds’ visible characteristics (like beak size) and invisible characteristics (like genotypic variation).
The Galapagos are subject to climate patterns that change sharply every few years, especially in terms of annual rainfall, as a result of the El Niño-Southern Oscillation. With these changes in rainfall come changes in vegetation: droughts cause small, soft seeds to be scarce, forcing finches to find other meals. During the the 1977 drought, finches relied on large, hard seeds, but only those with big, powerful beaks could successfully crack the larger seeds. Beak size is heritable, so the offspring of the drought-survivors inherited the trait for bigger beaks. The Grants’ quantitative studies made visible the surprisingly quick pace of evolution as they witnessed beak size expand after droughts or shrink after a bigger, stronger-beaked finch species arrived and competed for resources on Daphne Major. Their ground-breaking research proved that evolution could occur quickly and reinforced that it wasn’t unidirectional—that a physical trait such as beak size can increase or decrease depending on unstable factors in a species’ environment.
Rosemary Grant’s portion of the talk focused on speciation through reproductive isolation, mediated by song. On the small island of physically similar species, the finches learned to differentiate themselves by sound rather than sight. During Grant’s study, she observed that two closely related populations of finches, which could have successfully interbred but did not, sang different songs. As song recognition led to mating pairs, birds from each population became more genetically distinct, allowing their respective branches on the evolutionary tree of life grow apart. Interestingly, in both species—the medium ground finch and the cactus finch—only males sing. This prompted me to ask a knowledgeable friend if in general, only male birds sang. He replied, “Yes!”
My friend is an environmental historian and an expert birder, well-versed in both scientific literature and birding lore. Both arenas make assumptions about the role of birdsong. Charles Darwin pondered the function of song in bird behavior: did beautiful, complex tunes improve male birds’ odds of finding a mate and making babies? Darwin employed the concept of female choice in his theory of sexual selection: females chose among potential mates based on their positive attributes like clarity of voice and tune, leading to the evolution of complex song. Since Darwin, people—scientists and otherwise—have taken for granted that only male birds sing. The assumption fuels research questions that perpetuate it; for example, a 1987 evolutionary biology study asked whether male birdsong had a positive effect on mating success, and concluded based on their findings that “Darwin was right.”
More than a year passed, and I didn’t spend much time thinking about sex as it pertained to singing birds. My path to breaking through faulty assumptions came during a Tuesday night seminar covering research methods for thinking about the environment, the CHE Methods Seminar, at the University of Wisconsin-Madison.
During the seminar, Wisconsin Public Radio producer Craig Eley presented a guest lecture on environmental soundscapes. He discussed recordings of bird song, including songs recorded in open air and performances of birdsong by human whistlers. In an engaging analysis of gender and race in the context of whistling, we learned about famous women whistlers like Margaret McKee. We heard of how racial and gender stereotypes linked whistling to popular African American artists like George W. Johnson and to homosexuality. I asked if Eley had come across the ‘fact’ that birdsong is also gendered—only male birds sing. Wisely, Eley questioned the truth of my claim. “Was I certain?” he asked.
How could Darwin be mistaken?
Following my discussion with Eley, I double-checked my sources and discovered a 2014 article by Karan Odom, a doctoral researcher at the University of Maryland, with contrary information. Odom’s study found that “female song is present in 71% of surveyed [bird] species” (Odom et. al, 1). Contrary to the belief that only male birds sing, Odom et al. found that female song is not only more common than assumed, but was present in all songbirds’ most recent common evolutionary ancestor. This discovery upends the dominant explanation for the evolution of birdsong: that competition between males for female mates produced selection pressure to encourage song. If birdsong did not arise from pressures on males to perform for the ladies, new ideas about why some birds sing and some don’t could provide an even better match to the evolutionary pattern.
Odom’s article has been the source of reviews in National Wildlife Magazine, Science Daily, and Nature World News. Her findings—that a majority of female birds can and do sing—surprised me because I so frequently encountered the belief that only males sing. Geographic bias plays a role in this; in northern temperate climates, generally female songbirds don’t sing. In addition, in the Galapagos—where Darwin began to formulate his famous deductions—only male finches sing. Darwin was mistaken because of his incomplete geographical focus, which led him to extrapolate a universal theory from a limited sample. Unfortunately, the courtship behavior of male songbirds in northern temperate climes (and a few unique tropical islands) became the textbook examples for sexual selection and female choice.
The frequent presence of the idea that only male birds sing in public science writing and scientific research shows how ideas that can be true in specific cases become universalized despite the existence of contrary examples. Globally, both males and females sing, and this was likely true in the ancestral songbird species. Odom notes that the most ancient songbird is thought to have come from Australasia, where song is commonly performed by both sexes. But even geographic ‘rules’ regarding sex and birdsong have exceptions, including the northern cardinal (temperate, males and females sing) and the medium ground finch (tropical, only males sing). Despite this diversity, the idea that only male birds sing persists into the 21st century.
Environment, Biology, Society
Erika Milam, a professor in the history of science at Princeton University, wrote her dissertation on the concept of female choice as a mechanism of sexual selection within the history of evolutionary theory.1 Milam highlights the contentiousness of this idea during the mid-twentieth century, especially in regard to the females’ active role in mate selection, and how their choices shape the evolutionary process. Scientists in different factions grappled with questions like, “Does looking at female choice in animals attribute too much human rationality to their actions?” and “Does considering female choice in humans to be based on instinct degrade human action?” This overlap of biology and society, human and non-human—or more specifically, interpretations of biology and society and human and non-human —highlights the role of gender in shaping how we as humans perceive and move about in the world.
Historically, Western human social institutions have oppressed women’s voices. Similarly, female songbirds were theoretically robbed of their ability to sing by the faulty interpretations of predominantly male scientists. This example shows how the social relations of science shape theory, and why science needs to include a diversity of perspectives. My experience of having my birdsong assumptions corrected points to the importance of identifying and reexamining existing theories that were informed by dated, sexist ideas. Odom et al.’s finding that 71% of female songbirds sing is a significant discovery given that so many of us believed only male birds sang. What other conventional knowledge about the living world is misinformed?
Donna Haraway, Distinguished Professor Emerita in the History of Consciousness and Feminist Studies Departments at the University of California-Santa Cruz, writes that “sciences are woven of social relations throughout their tissues.” Silently, the social relations of Darwin and his successors maintained their bearing of truthiness within the idea of birdsong and sexual selection. What other aspects of the natural world are we reading through the lens of social relations? My journey with birdsong convinced me to keep wondering, keep asking. What will your experience in nature and society bring to light?
Featured image: A brown thornbill (Acanthiza pusilla), a species common in eastern and south-eastern Australia. Males are larger than females but have similar color patterns. Both males and females of this species sing. You can listen to recordings of brown thornbill song here. Image taken on September 3, 2013 by Flickr user patrickkavanagh.
Published in monograph form as Looking for a Few Good Males: Female Choice in Evolutionary Biology, Baltimore: Johns Hopkins University Press, 2010. ↩