A lifetime of noise: what are the costs?
Reference: Gurule‐Small, GA, Tinghitella, RM. Life history consequences of developing in anthropogenic noise. Glob Change Biol. 2019; 25: 1957– 1966. https://doi.org/10.1111/gcb.14610
Last summer, I was sitting on my apartment balcony with a friend having a pleasant conversation after a long day at work. It was a wonderfully still evening with hues of peach and pink being cast on the neighbourhood as the sun approached the horizon. In an instant, any unwinding and relaxation that I might have achieved abruptly disappeared with the grating high pitched squeal of my neighbour cutting a rock with an electric saw. It pierced through the otherwise quiet evening. Over the next half hour, not only did the noise disrupt the conversation, but I could feel my muscles tensing and my irritation growing. My experience is not unique. On a daily basis, we are exposed to a plethora of noises and it can have a profound effect on our health and well-being. Not only can it lead to hearing loss, but it can lead to stress-related mental health issues; impairment of learning, memory and focus; sleep disturbances; and an increase risk of heart disease. Noise created by humans (e.g. traffic) is a global problem. In the United States alone, vehicular noise is present in more than 83% of the entire continental landscape. This raises the question…..
How do animals respond to noise?
Thus far, research has found that animals experience stress in response to noise, much like I did last summer. Noise interferes with an animal’s ability to forage, take care of their young, as well as develop properly at early stages in their life. However, scientists have very little understanding of how animals respond to noise over a lifetime. Are they able to adapt and still thrive in their noisy environment?
Two scientists (Gurule‐Small & Tinghitella) from Denver, Colorado, USA wanted to understand if human made noise such as traffic influenced the survival and lifetime reproductive success of animals. To investigate this, they needed an animal they could observe in the laboratory from birth to natural death in a relatively short time span. The Pacific field cricket was the ideal candidate that fulfilled their experimental needs. Not only do crickets have a short life span (3-4 months), but they also represent a group of animals (i.e. insects) whose role contributes to the survival of many other animal populations in the environment (i.e. fish, birds, frogs). If insect populations are declining, the survival of other animals will be strained as a consequence.
It’s like music…I mean…noise to my ears
Traffic noise was specifically selected for these experiments because its low frequencies essentially masks the cricket’s song used to locate a mate. Traffic was recorded at 5 different locations in Denver, Colorado with varying vehicle density and speed limits. These recordings were then compiled into a single 5 minute track (a.k.a the masking noise). This same track was then digitally remastered to remove only the frequencies that overlapped with cricket’s song (a.k.a the nonmasking noise).
It took a lifetime
Shortly after the first moult, young crickets were placed in plastic containers within an incubator that had one of three sounds continuously broadcast throughout their entire lifespan: masking traffic noise, nonmasking traffic noise and silence. Their development, size, life span, and survival were recorded daily until their natural death. When crickets could be identified as male or female, a portion were utilized in a mating trial to gauge reproductive success. Each female was paired with a male from the same treatment group for 48 hours to mate. During this time, they continued to be immersed in the same acoustic environment as before. The males were subsequently removed, and the females were then given moist cotton pads to lay their eggs on. Researchers counted the number of eggs laid and recorded whether they hatched successfully.
Masking traffic noise delayed development and reduced the time spent as adult crickets. Not only did it take them 11 days longer to reach adulthood, but they also died 9 days sooner than those raised in silence. Crickets in nonmasking traffic noise took 7 more days to reach adulthood but spent the same number of days in adulthood as those raised in silence. Surprisingly, the type of acoustic environment had no effect on survival to adulthood, growth and lifetime reproductive success. Overall, males lived longer than females and females that mated lived longer than those that didn’t regardless of acoustic treatment.
Animals adapt to changes in their environment; however, there is usually a cost associated with their continued survival. Crickets exposed to traffic noise spent a longer time as developing juveniles which may have allowed them to reach adulthood in the laboratory. In the wild, prolonged development increases the probability that they will become food for something. Moreover, a shorter adult life span decreases the time that a cricket is able to locate a mate and produce offspring. These research findings indicate that crickets and insects in general may struggle to survive and thrive in noisy environments. A loss of insect populations may not seem so bad to some, but they are the building blocks of a healthy environment. Without them, nature’s more beautiful creatures cannot survive.