Bats can ramp up their heart rate to 900 beats per minute

For the first time, a team of researchers measured the heart rate of bats over several days in the wild, including full flight recordings. 

The study involved attaching heart rate transmitters weighing less than one gram to male common noctule bats. 

The bats were tracked while they flew in search of food, with scientists following in an airplane for more than an hour at times. 

Energy consumption of annuals

The findings, published in the journal Proceedings of the Royal Society B, reveal significant insights into the energy consumption and survival strategies of bats.

The study was led by researchers at the Max Planck Institute of Animal Behavior (MPI-AB) and the University of Konstanz. The goal was to understand the energy expenditure of male common noctule bats throughout the year. 

“Understanding how animals meet their daily energy requirements is critical in our rapidly changing world,” wrote the researchers.

“Small organisms with high metabolic rates can conserve stored energy when food availability is low or increase energy intake when energetic requirements are high, but how they balance this in the wild remains largely unknown.”

Energy budgets of bats

Study lead author Lara Keicher, an ecologist at Max Planck, noted that bats are fascinating animals that often share their habitat with us humans.

“But bats are still shrouded in mystery. We don’t yet have a clear answer to simple questions such as: How much food do they need and can they find enough of it in different seasons to survive?”

To gather data, scientists fitted bats with heart rate transmitters weighing only 0.8 grams. 

“To understand and accurately quantify energy budgets of bats in different stages of their life cycle, we studied free-ranging male common noctule bats, Nyctalus noctula, in southern Germany,” wrote the researchers.

“Nyctalus noctula is a representative insectivorous temperate-zone bat species with an annual life cycle characterized by periods of torpor and hibernation that are timed around different stages of the annual reproductive cycle and seasonal insect availability.”

Tracking the bats’ heart rates 

The transmitters, which the bats wore for a few days, emitted audio signals of the bats’ heartbeats, recorded using a radio receiver. This method allowed the researchers to track the bats’ heart rates within a few hundred meters. 

During the day, the recordings were straightforward as bats rested in tree caves or bat boxes. However, nighttime tracking required the researchers to fly a small airplane to follow the bats during their hour-long flights.

The researchers found that bats’ heart rates could reach around 900 beats per minute during flight. “It sounded like a single high-pitched tone to our ears,” Keicher said. 

Energy conservation strategies of bats

The study revealed that male common noctule bats use different energy conservation strategies depending on the season. 

In spring, the bats enter a state of torpor, reducing their heart rates to as low as six beats per minute to save energy. “We saw that bats in spring could ramp up their heart rates when they wake up, reaching the top speed of 900 beats per minute within only a few minutes,” Keicher added.

Interestingly, the team discovered that male bats do not use torpor during the summer. 

“In the warmer months, when food is plentiful, males stay awake during the day to invest energy in sperm production in order to be ready for mating in the autumn,” she explained. 

To compensate for the energy expended, male bats hunt twice as long in summer, consuming up to 33 June beetles or over 2500 mosquitoes in one night.

Energetic challenges faced by bats 

The findings highlight the energetic challenges faced by bats and their survival strategies. This understanding is crucial for predicting how bats will be affected by climate change and changes in food availability. 

“All bat species are protected in Germany and some are threatened with extinction. Basic research that investigates the behavior of the animals and their adaptations to the environment can help us develop protective measures,” concluded senior author Dina Dechmann, a biologist at Max Planck.

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