Is summer the human mating season

Sleep until spring comes

The year in the life of a bat

Bats overslept about half of the year! They hibernate from the beginning of November to the end of March. They have to, because the menu of our native bats invariably includes insects that are in short supply in winter.

Batyear - the year in the life of a bat - Graphic: NABU / Matthias Schöbe


Fall asleep in the fall

It is autumn. The days are getting shorter and the nights longer. One would think the ideal time for long bat trips. However, no bat can be seen in the night sky. And there is a simple reason for this: bats overslept about half of the year! They hibernate from the beginning of November to the end of March. They have to, because the menu of our native bats invariably includes insects, which unfortunately are in short supply in winter. By the way, bats belong to the mammals that hibernate “properly”. In contrast to squirrels and brown bears, for example, whose hibernation is more of a hibernation that is interrupted once during the winter, bats only rarely wake up in winter and then do not actively look for food.

In order to be able to go without food for up to six months, the little fluttering men put on 20 to 30 percent of their weight in the autumn. In late autumn, bats go to their winter quarters - here they prefer sleeping places that are cool and damp, but frost-free. You can find them in caves, tunnels, bunkers or cellars. In winter, females and males live together in their roosts, while in summer the sexes live in separate places.


Five months on the back burner

Large mouse ears in winter quarters - Photo: NABU / Christian Stein

Bats lower their body temperature to five to three degrees Celsius in winter. To do this, they slow the heartbeat and breathing down by 40 times in extreme cases. In order to keep the heat loss as low as possible, many of them snuggle up close to their fellows or crawl in cracks and crevices. In addition, some of them wrap themselves in their flight skin like a coat. When the ambient temperature falls below the body's drastically lowered sleeping temperature, bats have to “re-heat” - at the expense of their fat reserves, which they have eaten up. As a result, the “beauties of the night” lose around 30 percent of their weight during the winter.

Any disturbance of hibernation can accidentally wake the animals. Bats need 30 to 60 minutes and plenty of calories to warm their bodies to operating temperature. That goes to the laboriously pitted fat pad. That is why many bat caves are closed to visitors over the winter. Because if the little flying artists wake up too often in winter, it can happen that their reserves are no longer sufficient until spring and they die.


Big awakening in April

Large mouse ears - Photo: NABU / Christian Stein

The active season for bats usually begins in April: after they have awakened from hibernation with the first rays of sunshine, they go to their summer quarters. In doing so, they sometimes cover great distances: the roosts of the noctule bat and the common noctule bat are very far apart at over 1,500 kilometers. Most species, however, usually “only” fly 200 to 300 kilometers or, in the best case scenario, simply change their hanging place from the basement to the attic - such as long-eared ears.

The bat women are then pregnant in their summer quarters - in the absence of the men! Yes, it actually works. Because after mating in September and October, the egg cells are not fertilized immediately. The sperm survive in the female's genital tract for many months. Only after waking up from hibernation does ovulation and fertilization occur - then there are enough insects again, the basic food for our bats and known to be in short supply in winter. If the food situation or the weather in spring is unfavorable, the time of birth is even postponed.

In order to give birth and raise their young, the female bats of a species join together to form nursery groups. Usually these groups consist of around ten to twenty animals. However, several thousand females have already been counted in one roost in the case of the great mouse-eared mouse. The young are born after a gestation period of around 50 days and weigh just two grams for small species! They are suckled and start hunting insects on their own at four to five weeks. The males spend this time either individually or in small colonies of males. Only rarely and in northern regions do males live sporadically in the nursery.


Courtship with ultrasound

Gray long-eared, eating - Photo: NABU / Dietmar Nill

Shortly after the boys move out in mid-September, the bats are busy with the next production of offspring in what are known as courtship quarters. During this time the male bats occupy tree hollows along the migration routes of the females. These caves are only left briefly and defended against other males. With their typical courtship calls, the male bats now lure the females to mate.

While the bats are still busy with family planning, there is one thing they must not neglect: the big feed! From September to around the end of October they have to get good fat reserves, because in November they go back to their winter quarters for their next hibernation.


Bats get very old: 20 years and more are not uncommon. The pipistrelle, for example, lives on average for just under 2.5 years. However, even the smallest of our bats can live up to 16 years. The ringing of a large mouse-eared mouse even attested to an age of 25 instead of the average four years.

Bats usually do not die of natural causes, but fall victim to human influences such as the loss of their habitat or traffic.

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