Bats can tell that air over the urban areas is warmer than air over parks

An Egyptian fruit bat. Photo: Tel Aviv University (TAU).

TAU study calls bats "a flying meteorological station"

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In a creative collaborative effort between zoologists and geographers from Tel Aviv University (TAU), a new study utilizing bats to map “Urban Heat Islands” in the Gush Dan metropolitan area of Israel reveals that the air over the Ayalon Highway can be up to 5° Celsius (41° Fahrenheit) warmer than the air in Yarkon Park during the winter months.

The interdisciplinary study was led by Professor Yossi Yovel and Dr. Aya Goldshtein of the Bat Lab for Neuro-Ecology at TAU’s School of Zoology, Sagol School of Neuroscience, and Steinhardt Museum of Natural History, in collaboration with Professor Alexandra Chudnovsky, Professor Oded Potchter, and the late architect Dr. Limor Shashua-Bar of TAU’s Porter School of Environmental Studies. The research findings were published in the June 2023 issue of Applied Geography.

“Urban Heat Islands are a well-known urban phenomenon,” Professor Chudnovsky explains. “These are dense urban areas that are several degrees warmer than their surroundings. However, for objective and environmental reasons, it can be difficult to measure them. Placing stationary measuring stations on every street is nearly impossible, and deploying individuals with mobile sensors requires significant financial resources. Furthermore, measuring stations only capture ground-level temperatures and don’t provide a 3D temperature analysis. One potential solution is using drones, but permits to fly drones in urban areas and flight time limitations pose challenges.”

In the current study, the research team decided to leverage the unique capabilities of bats, known for their exceptional navigation skills and familiarity with urban environments. “Bats are more adept pilots than drones,” says Professor Yovel. “They can fly 100 kilometers [62 miles] in one night, and they are active at nighttime, exactly when the heat island phenomenon is at its peak.”

For the experiment, the researchers attached tiny heat sensors to Egyptian fruit bats from an urban bat colony and released them in downtown Tel Aviv. The clever bats easily found their way back home, and on the way back they mapped air temperatures over different areas, including the city center, the Ayalon Highway, Yarkon Park, and Herzliya. The experiment was conducted during the winter, between 8:00 pm and 2:00 pm, revealing temperature differences of two to five degrees Celsius between dense urban areas and city parks.

The researchers compared the data transmitted by the bats to readings from four meteorological stations in Tel Aviv. Simultaneously, the researchers conducted a large-scale field experiment using mobile meteorological stations to verify the data. They also equipped individuals with similar devices and sent them to different parts of the city to collect comparable measurements.

“These are very light temperature sensors, weighing just 0.2 grams, so they are not as accurate as a heavy meteorological station,” Professor Chudnovsky says. “But their advantage lies in their providing a comprehensive climatic picture in a short timeframe. An analysis of the measurements revealed significantly higher temperatures in the Ayalon area compared to Yarkon Park, where temperatures dropped. As the bats crossed Yarkon Park towards Herzliya, temperatures rose again. Thanks to the bats, we were able to create the first three-dimensional map of Urban Heat Islands in Gush Dan.”

The TAU researchers call their innovative approach as “Biologically-Assisted Sampling” and plan to extend its application to other species. “We must utilize any mobile platform that can assist us,” says Professor Chudnovsky. “Just as the bats helped us map Urban Heat Islands, pigeons can be used to effortlessly map urban air pollution, saving us a great deal of money and years of painstaking research.”

“There’s a lot of talk about smart cities and the ‘internet of things,’” Professor Yovel adds. “But there are many animals already roaming the city, and we can attach tiny sensors to them without affecting their behavior. For example, when monitoring pollution in sewage systems, we can rely on the rats that are already present there rather than using expensive and complex machinery.”

“Just as the bats helped us map Urban Heat Islands, pigeons can be used to effortlessly map urban air pollution, saving us a great deal of money and years of painstaking research.”