How do birds cope with our increasingly noisy world?
The world is a noisy place, and that can pose problems for animals that depend on hearing each other’s sounds to find out about food, predators, and mates. Many species of mammals, birds, fish, and frogs produce louder, longer, or higher-pitch calls in noisy places, to be heard above the noise. But those altered sounds may not be good enough – they may not travel as far or convey the same information as normal songs.
People respond to noise in similar ways. Imagine yourself in a busy room, perhaps a classroom full of young children or a large family gathering. Now imagine you are trying to speak with someone across the room. You may wave to get their attention, call their name with a raised voice, and once you do get their attention you may choose to keep your conversation brief or abandon it altogether if the noise level is too much to overcome. The phenomenon of speaking louder when it’s noisy is called the Lombard effect, and we see this unconscious response to noise in many animals.
While scientists have shown that individual animals signal differently when the environment is noisy, we don’t yet know how these changes affect communication in groups of animals. The daily lives of group-living animals is action-packed, with females eavesdropping on song contests between rival males, males “bragging” when certain females or males are within earshot, and other methods of acquiring information about mates and rivals from group communications. How noise affects the transfer of information and the size of the networks within which animals communicate is the central goal of my research.
In the spring and summer of 2014, I recorded neighbourhoods of birds in 10 Ontario Parks in southeast Ontario, including Balsam Lake, Silent Lake, and Sharbot Lake Provincial Parks. At each park, I set up groups of automated recorders with small microphones that I programmed to record from before sunrise until late-morning, to record the peak of daily singing activity for many species of birds found at the parks. I used a sound-level meter to measure the noise level at each park, and I will compare both the songs that birds produce and how birds communicate with one another in parks that differ in noise levels. Some of my recording sites were located beside busy roadways, like at Darlington and Mark S. Burnham parks, and others were in relatively undisturbed areas beside low-volume country roads, such as Peter’s Woods.
Surprisingly, my early results show that the overall noise levels across the parks were not as different as I expected. After scratching my head about why this may be, I’m looking forward to diving into my sound recordings to see exactly where the sound energy falls within the acoustic space at each park. I suspect that parks near busy roads will have a lot of sound energy concentrated in the low-frequency range, due to the low rumble of traffic, whereas parks away from roads may have more sound energy concentrated up in the higher-frequency ranges, produced by vocalizing insects and other animals.
I’m interested to look at the songs of certain species that live at most or all of the parks I visited, like Black-capped Chickadees, to see in what frequency range they are singing and compare that to where the most sound energy is concentrated at each park. I think that their songs might be a little higher frequency in areas with loud traffic noise compared to more pristine areas. I’m also going to look within my network of microphones to gauge how far apart the singing birds are spaced, and how many neighbours they regularly interact with. I predict that in noisier parks birds will either communicate with fewer neighbours or birds will gather in tighter groups so they can hear each other above the noise.
The increase in human activities around the world has caused a recent and dramatic rise in low-pitched noise levels. Ontario Parks offer much-needed pockets of relatively pristine habitat for our native animals, especially in highly-developed southern Ontario. The effects of noise are far-reaching, however, and might be particularly problematic for species at risk, potentially further limiting the suitable habitat available for them to live and breed successfully, and adding another challenge to their struggle for survival. Learning how animals respond to noise may help us protect them.