Presenting – The bat. A one-of-a-kind animal

To broaden our view of the biological world, we are exploring a unique animal – the bat.

We know of 5000 species of mammals worldwide. Amongst them, there are more than 1200 species of bats, making bats the second biggest group of mammals after rodents.

Flying

For many reasons, bats constitute a unique group of animals. Firstly, bats are the only mammals able of active flight. Their wings are made from skin stretched across bones that are homologous to the ones in our fingers. The patagium is the membrane that forms the bats’ wings, allowing them to fly. It is made of epithelial tissue and is the fastest regenerating tissue in the animal kingdom. This characteristic is essential, as the integrity of the wings is vital for a bat. The patagium is well vascularized but does not contain any nerve endings.

Wing membranes of Townsend’s big-eared bat.
HTTPS://EN.M.WIKIPEDIA.ORG/WIKI/BAT#/MEDIA/FILE%3ABIG-EARED-TOWNSEND-FLEDERMAUS.JPG

Diet

Bats constitute an extremely diverse group, with species of highly variable sizes, habitats, and diets. For example, some bats eat nectar or fruits, many catch flying nocturnal insects, others eat fish or hunt small mammals or birds. Three species of bats feed on blood, usually by wounding from livestock, but they are found only in Mexico, central and south America (1). Being the size of a teacup, they can’t do much harm to humans, don’t worry.

Interestingly, bats are also a huge regulator for nocturnal insects, a group of animals with few predators.

Echolocation

Contrary to popular belief, bats see very clearly (2) – they use their vision to navigate previously explored territory. For hunting, most bats use echolocation. They emit high frequency sound waves that bounce off their pray, providing information on its localization. With echolocation, bats can detect minuscule objects, down to the size of a human hair.

Habitat and Colonies

Bats are found throughout the world, apart from in Antarctica. There are even species that can reach the artic circle! (3) Most of the diversity in bats, like in many other species, is found around the equator.

Bats are very sociably and live in colonies that can be made up of thousands of individuals. Different species of bats tolerate each other well and can often share the same territory. Sometimes, there are even different species of bats present in the same colony.

Life Cycle

During winter, when there are no insects to eat and the temperature dips under 10°C, bats hibernate. They do so in places that boast cool and stable temperatures, such as caves or old hallowed out trees in a dark forest. When they settle down to hibernate, their body temperature drops from 37°C to the temperature of the surface they are griped onto, reaching 0°C at the coldest. Their cardiac rhythm and their breathing slow down, and they remain dormant for multiple months. When they awake, it takes them about an hour to warm up enough to be able to fly, as they burn large quantities of brown fat to elevate their body temperature.

Sometimes, bats do briefly wake up halfway through hibernation, to have a drink of water for example. But since there is no external source of energy available (few nocturnal insects are present during European winters), the hibernation breaks are brief.

During April and March, bats wake up from their hibernation and go to their summer roosting sites.

The females return to the place where they were born and make gather there in a colony, called a maternity roost, to give birth to their offspring. Maternity roosts can be found in old trees with thick bark or in small, dark spaces found in old buildings for example.

During this time, males live a more solitary life and are not involved in the care or education of the young bats they have fathered.

From the start of May to the end of August, females give birth and raise their offspring. Each female gives birth to one baby per year (with some rare exceptions, like twins in some species). The birth takes place in a warm environment, such as dead trees in a forest of deciduous trees or even in an unused chimney, as the offspring are tiny and don’t have any hair to insulate themselves. The babies then crowd together in the colony, allowing them to maintain their temperature. During this period, the offspring are breastfed by their respective mothers for around a month and a half.

In the months of September and October, the reproduction period, during which males and females copulate, takes place in swarming sites, such as huge caves. In swarming sites, thousands of individuals can be found – it is there that the genetic mixing takes place.

SWARMING BATS.
https://www.businessinsider.com/bat-tornado-cave-2016-3?r=US&IR=T

Since the female bats cannot grow a baby while they are hibernating, many strategies have evolved to delay the pregnancy until the following spring. For example, in some species, ovulation is delayed, and the sperm is stored in the female bats reproductive system, whilst in others ovulations persists but the sperm is stored in a pouch in the females abdomen, separated from the egg. Both these methods result in delaying fertilization, which then takes place a couple of days after hibernation ends. In other species, fertilization occurs in autumn, but cell divisions cease very quickly, and implantation of the egg occurs only in the spring (4).

In autumn, bats also hunt extensively to accumulate the fat necessary for hibernation. Then, they migrate to their hibernation site for the winter.

As you can see, bats need to visit many specific locations to complete their life cycle. If disruptions occur in any of the key locations, this can be catastrophic for a bat population. To protect bats, we need to focus our conservation efforts on roosting sites, swarming sites where copulation occurs, and hibernation sites.

Preserving the Bats

Bats, as many other groups of species, have currently been greatly endangered due to the rise in human presence and climate change. Pollution and climate change are of course a huge issue for bats. Another problem that has come with human presence is light pollution – some species have become drastically less common due to this problem (5). To remediate this, we can reduce public lighting in towns and cities and as individuals we can turn off the lights in our personal homes. We can also set up dark pathways – as in areas that do not have public lighting – between forests or other bat habitats to allow the transit of bats.

Pesticides can have huge effects on bat populations, whether it be because of the toxicity of the product or the impact they have on their food source (6). The lack of nocturnal insects due to the rise of pesticides used in agriculture represent a huge loss of food for some species of bats. To help with this issue, we need to move towards more sustainable types of agriculture, avoiding monocultures and the use of chemicals to kill insects. As individuals, we can vote with our dollars by choosing to purchase from organic farmers that put an emphasis on crop diversity, leading to insect diversity.

Some bats have adapted to human presence and use our building or chimneys as roosting sites. It is imperative that we not destroy these precious habitats. To preserve the buildings that house bats, we need to first raise awareness about these wonderful creatures, so that they are no longer feared but become valued and respected.

References

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