Section 1.1: The Impact of Urban Noise on Animal Communication

Just like humans, various animal species prefer lower mating calls from males. Pitch, measured in hertz, refers to how often a sound wave oscillates per second. For instance, city traffic typically ranges from 1 kHz to 10 kHz, with the lower end coinciding with the pitch of many deep and appealing mating calls in species such as grasshoppers, frogs, robins, and wrens. Research indicates that some of these species have elevated their mating call pitches to adapt to urban noise. Frogs, for example, have increased their calls by about 5%, while grasshoppers have raised theirs by roughly 4%.

As with us, many animal species find lower calls attractive. Female red deer, for instance, prefer males with resonant roars, while the usually reserved male koala produces a low, rumbling mating call. The blacktail shiner fish also uses a deep growl to attract mates. Although not extensively studied, there is evidence suggesting that lower-frequency calls indicate a male's physical and sexual prowess. Research links low-pitched calls among male birds, primates, frogs, and other species to larger size, elevated testosterone levels, and sexual maturity.

This leads some researchers to ponder whether noise pollution from human activities disrupts animal mating behaviors. When forced to increase the pitch of their calls, crucial information may be lost, making it more challenging for females to identify the most suitable mates. “Females might be making suboptimal choices,” notes Kirsten Parris, a researcher at the University of Melbourne studying urban noise's effects on amphibians. “They might miss that Bob has more energy than Frank,” she adds, indicating that choosing a less vigorous mate could diminish reproductive success.

Section 1.2: Evidence from Studies on Mating Calls

A few studies validate these concerns. In 2010, researchers studied egg-laying patterns of great tits along a busy street in the Netherlands and found that females produced about 10% fewer eggs when exposed to traffic noise in the 2 kHz range, which overlaps with the lower frequencies of their mating songs. Even after considering other variables like proximity to traffic and tree density, the frequency of traffic noise emerged as the best predictor of clutch size. The noise likely interfered with females’ ability to hear male songs, hindering their mate selection.

In 2006, another study tracked the pairing success and age distribution of male ovenbirds near noisy compressor stations in Alberta, Canada, compared to quieter areas. It was observed that significantly more inexperienced birds attempted breeding near the noise sources (48% versus 30% near silent locations). Moreover, pairing success was notably lower in noisy environments, leading researchers to suggest that noise may distort male songs and obscure their quality.

Despite these findings, not all scientists are convinced that noise impacts mating calls or that pitch adjustments are effective in mitigating noisy environments. Sue Anne Zollinger of the Max Planck Institute for Ornithology argues that while it's widely accepted that animals may increase pitch to avoid noise, the reality is less definitive. In a review of bird mating calls, she found that less than half of the 56 species studied showed pitch differences in noisy settings.

Hans Slabbekoorn, an associate professor at Leiden University, acknowledges evidence for noise-dependent pitch shifts among various species but cautions that not all will adjust their calls. He emphasizes that while a higher pitch might enhance a male's call audibility, it remains uncertain whether such adjustments truly benefit the species, given potential losses in signal quality. Future longitudinal studies may clarify the trade-offs of adapting to noise and whether a pitch change provides a solution. Parris is also investigating whether noise has contributed to pitch increases in grass frogs, potentially leading to a loss of critical information and contributing to their decline.

While researchers continue to explore these issues, we can glean practical insights from their findings. If you’re on the lookout for a partner and wish to present your best self, consider avoiding situations that require raising your voice. Opting for a quiet stroll in the park may yield better results than trying to make yourself heard in a noisy club.

Jenny J. Chen is a science writer based in Washington, D.C. Her work has appeared in outlets such as The Atlantic, Washington Post, and NPR.