In the spring of 2020, when many countries initiated lock downs, the wildlife experienced a different environment — one without humans. The phrase “nature is healing, we are the virus” spread across the internet, as media outlets reported more wild animals sightings in city streets and the choruses of whales speaking to each other without the din of boats.
Now, in 2021, a year after the initial lockdowns, researchers are digging into the data to figure out how a change in human behavior, like the sudden halt of commuting and large gatherings, change the behaviors of animals that share our spaces. Some researchers found that birds were not as afraid of people wearing masks and that the lack of human-made noises changed the noises the birds made. And a new study by Ming Kai Tan and Tony Robillard aims to understand how our lockdowns affect the sounds of an animal many of us take for granted, the cricket.
Originally, the researchers hoped to compare cricket behaviors between populations of common crickets in Singapore. They collected the crickets, recorded their calls, then exposed the crickets to different environments to measure any changes in their calls. Then, partially through the experiment, Singapore locked down for 7.5 weeks and they had to put the experiment on hold.
But all was not lost. Being resourceful scientists, the researchers used the lockdown as an opportunity to study how the sudden halt of human activity altered the crickets’ calls. They had the data from before the lockdown, and once restrictions were lifted, they could collect data from after.
The cohort of cricket collectors in Singapore recorded the calls of the crickets in three different parks around Singapore, representing three different populations with different levels of human disturbance. Hindhede is a park near dense urban housing in the center of the city. Ubin is located on an island offshore and Labrador is located near the bustling business district. They measured the call duration and found that each population called for a different amount of time. The two month lockdown did not change the duration of the calls for any of the populations.
The trill duration, however, was affected by the lockdowns. The cricket trill usually occurs at the end of the call and is easily recognizable by predators. Trills take more energy to produce and it may not be beneficial for crickets to extend their trills when they need energy to deal with local disturbances, like people. In Hindhede Nature Park, located in the center of Singapore, the crickets trilled for a shorter period of time after the lockdown. This phenomenon was not observed in the other two populations with lower human population density.
The researchers hypothesize that the difference in call and trill duration between the populations is due to evolution within these populations due to different levels of human pressure. The sites with the shortest calls were also the sites with the most human activity before the COVID-19 lockdowns, such as hiking and biking through the parks. Hindhede Nature Park may have been the only place where crickets responded to the lockdown because due to its location near the city center, it historically faced the most human activities and disturbances. Additionally, since the park is located near dense housing, visitation surpassed the numbers pre-lockdown due to teleworkers escaping to the nearest nature patch while working from home. Even after the initial lockdown, Singapore residents were less likely to visit parks on the island offshore and in the business district because they preferred to stay closer to home and avoid travel.
Over the next few years we can expect more studies like this, studying the effects of a sudden and global halt of human activity on wildlife populations. It is rare in ecology to have a natural experiment like this and we all hope something like this never happens again. But with some creativity and flexibility, scientists were able to use lockdowns to answer interesting ecological questions.
Source: Tan, M. K., and Robillard, T.. 2021. Population divergence in the acoustic properties of crickets during the COVID-19 pandemic. Ecology 102( 7):e03323. 10.1002/ecy.3323