Many years ago, when we were renting a house in a town outside of Seattle,…
Scientists are studying the psychological benefits that accrue when people listen to the sounds of birds. It is thought that hearing birds sing may help us to relax and recover from stress, assist our focus on tasks, and inspire us to think creatively. Given our deep connection to birdsong in poetry, music, and our daily lives, people would be wise to try to understand the potential impact of human activities on this behavior.
The prevalence of artificial light at night disrupts the normal daily biological (circadian) rhythms of many animals (including us). Because of artificial lighting, the dawn chorus has been shown to occur earlier than in the past, especially by the more light-sensitive early singers, and some birds are not joining in at all. Rather than waiting until dawn, birds may sing during the artificially lit night. There are documented nighttime recordings of songs that historically were heard only during the day. Certain birds may benefit—getting an early start on the day because of streetlights at the edge of a forest has enabled some blue tits to be more successful at attracting females. However, others may not be so lucky, especially if the nighttime disruption increases energy expenditure or disrupts sleep. It has long been known that reproductive hormones are important to both the production of and response to birdsong. Artificial light has been found to cause a decrease in the production of reproductive hormones in birds, which may in turn affect birdsong and the ability to select a satisfactory mate.
Cities are noisy places and this may affect vocal communication in birds. Research has shown that birds that live in urban environments sing in higher frequencies than their counterparts living away from cities. Not only are the higher frequency sounds easier to hear above the rumble of traffic, but it turns out that birds can produce higher frequency sounds at a higher volume. They basically have to shout to be heard when they live in the city, and it’s easier to do so when singing at a higher pitch. Birds may also change their timing to avoid singing during rush hour. Although some bird species are capable of producing song that is better heard in the city, the overall picture is not good; a Canadian study concluded that the higher the noise level, the fewer the number of bird species living in a given area.
Recent research has highlighted the ill effects of chemical contaminants on birdsong. For example, most birds along a mercury-polluted river in Virginia sing simpler, shorter, lower-pitched songs than noncontaminated birds. The extent of the effect is wider than originally thought—even birds in that ecosystem that don’t eat fish suffer from high mercury loads (many area songbirds are getting the mercury from eating spiders). Another study in England revealed that birds near a smelter (that emits heavy-metal pollution) learn fewer songs and sing less than birds from nonpolluted sites. Likewise, chickadees exposed to polychlorinated biphenyls along the Hudson River in New York show poor vocal performance. On the flip side, starlings exposed to estrogen-mimicking chemicals (such as bisphenol-A) sing more complex songs. Although this is a boon to those particular males, it is not good for the starlings overall. Contaminated males have poor immune systems, yet they are the ones being chosen by the females due to their chemically enhanced song. Normally, complex songs represent a high-quality male to a selective female and she would be improving, rather than reducing, her chance of producing healthy offspring by selecting such a male. One of the main functions of birdsong is to advertise quality to a potential mate, and the human-induced changes in song may have negative long-term consequences on bird populations.
It turns out that birdsong matters to the birds. And it matters to us. Rachel Carson first alerted us to the dangers of chemicals in her 1962 seminal work Silent Spring, and recent evidence warns us that we still need to pay attention to these issues if we want our world to be filled with the delightful songs of birds.