July 24, 2024, 8:18 am | Read time: 4 minutes
When the common noctule glides through the night, hardly anyone thinks about its extraordinary talent: the endangered bat can increase its heat rate from an almost non-existent six to an incredible 900 beats per minute. A study has now revealed how it manages this and why its testicles grow in the process.
The thought of bats might not inspire cheers, but rather send shivers down the spine for many. Books and films have often portrayed these nocturnal creatures in a way that has led to an unfounded fear. This is compounded by their elusive nature and the mystery that surrounds them. However, after a new study by the Max Planck Institute of Animal Behavior, hopefully no one will be afraid of the common noctule anymore. These endangered, native bats can use clever tricks to increase their heart rate from 6 to 900 beats per minute. PETBOOK reports below on how these animals achieve this and why their testicles enlarge as a result.
Bats lower their heart rate during mini-hibernation
The common noctule is a native bat species that lives mainly in forests. It is one of the largest species in the region, boasting a wingspan of up to 40 centimeters (ca. 15.7 inches). Instead of sucking blood, it feeds on beetles, butterflies, mayflies, and other smaller flying insects, according to the Federal Agency for Nature Conservation.
A study by Lara Keicher and her colleagues, which appeared in the journal “Proceedings of the Royal Society B”, shows that it does this in different ways depending on the season and is particularly prolific in the summer. In order to investigate the lifestyle of the common noctule, they used tiny probes to record the heartbeats of male bats in the greater Constance area.
The researchers were thus able to show that bats still go through phases of inactivity even after hibernation, as well as how the phases progress. These short phases are called torpor and are used when the food supply is still very scarce. According to the data from the probes, the common noctule can reduce its heartbeat to six beats per minute in order to save energy. It also slows down its metabolism and its overall calorie consumption.
In summer, male bats engage in competitive behavior
However, when the insect population is high in summer, the common noctule is at its peak. The researchers were able to document that the bats then increased their heart rate in flight to up to 900 beats per minute. This is because in the warmer months, they hunt more than average and use a lot of energy. It’s akin to a bat fitness competition, where each strives for peak performance and maximum protein intake.
But what is the purpose behind all this activity? You have to take a closer look at the bats’ way of life. Males and females spend most of the spring and summer apart. The females fly north to give birth and raise their young. Meanwhile, the males begin to spur each other on in groups of up to 20 and pump each other up. In the truest sense of the word. They even change their nocturnal routine in order to catch as much prey as possible during the day. Not only does their heartbeat become much faster, but their blood starts to circulate and their testicles swell.
This phase in the bat’s year is called spermatogenesis. During this time, the testicles can increase to up to eight percent of the bat’s body mass, according to the study. All the extra energy is needed to start the mating season again in the fall. Until then, the body temperature is kept high in order to increase the growth of the testicles. Increased quantities of germ cells are then produced in the highly active tissue.1
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These are prepared for when the females return in late summer. However, how much energy the females have invested in reproduction and rearing up to this point still needs to be investigated. This is because in this first study, only the site-loyal males were analyzed.
However, it is known that mating is followed by a phase of “big feeding”, during which females and males prepare for hibernation together. During this time, the females store the sperm released to them until they impregnate themselves at the beginning of spring. The process then starts all over again.
The insights gained from the study can contribute to the long-term protection of the endangered common noctule. Because if we understand how they use their energy and when they need a particularly large amount of food, we can support and preserve the species, which is considered endangered in Germany, even in times of climate change.