It is 6:00 a.m. in Konstanz, Germany. It’s March and spring has arrived a bit too early for everyone. The weather is a little unpredictable; windy, cold and rainy days are squeezed between some sunny days.

I am getting ready for another adventure with researchers from the Max Planck Institute of Ornithology (Dechmann Lab). Lara, a new Ph.D. student, is going to lead the charge today. The team includes Marion (technician), Pino (enthusiastic but quiet dog), Lucy (a visiting scholar from the Czech Republic, studying rodents and insectivores) and Klaus (director of a local volunteer group for bat box monitoring).

We are going towards Mainau ‘Der blumeninsel’ which literally translates to the Island of Flowers. The park is famous for its spectacular flower gardens and its rich collection of plants, trees and exotic butterfly exhibitions in summer.

Thousands of people flock to this venue from many countries throughout the year, to enjoy the scenic beauty of the island. The island is also home to many resident species of birds, and harbours wintering water birds from the far ends of Europe during winter. This island also happens to be the choice winter hibernation spot for hundreds of bats.

Amateur data collection is invaluable


Lara invited me to join her for bat box monitoring. The team met at 6:30 and rushed towards Mainau. The sun was just coming up and Klaus was already waiting for us near the carpark.

Klaus is a retired person volunteering to monitor bat boxes in the region. There’s a group of volunteers who follow their passion for wildlife and contribute to maintaining records of bat populations. They are not necessarily academic researchers, but their approach is very methodical and their knowledge and data collection is invaluable to scientists. This reminds me of a famous article from The New York Times, titled “The German Amateurs Who Discovered Insect Armageddon.”

Klaus is holding a data sheet on which we are going to record the number of bats we find in the boxes. Each box is numbered, and we will check some 30 boxes, as well as recording other details whenever possible (i.e. species, sex, weight, etc.).

Lara recently started her Ph.D. and she is going to study a specific species of bat—the common noctule (Nyctalus noctula).

She needs some bats for two to three days for her experiments, which will measure their body temperature, heart rate and metabolic rate in the lab. She is investigating how bats save energy at different stages of their life.

Bats in this temperature zone hibernate in winter and reduce their activities, including foraging for prey. When temperatures rise in spring, they become active and forage, and females give birth in summer.

During the active phase, they switch to a commonly used strategy to save energy. They use daily torpor, which is a temporary energy-saving mode in which they reduce their energy consumption by regulating their heart rate, body temperature, metabolism and such.

Mammals need to regulate their body temperature and keep warm, which demands lots of energy (= food). Often, their prey is only available at certain times of the day, which means they cannot eat continuously, so they regulate their energy requirements. It is like switching off your electrical appliances when they’re not needed, because they consume electricity that is costly and limited.

This is an active field of research, and my explanation is a simplified version of the process. We still do not know the exact details of torpor and how bats are using it.

An ideal field site


Today, Lara is out to check if the bats are waking up from hibernation and becoming active. In early summer, the female bats will migrate towards other European countries (the Netherlands, Poland), leaving the males behind.

The relatively stable population of bats makes this place an ideal field site for Lara, as she knows that she can find bats here for her study.

It is critical for Lara to take the measurements of both sexes before and after the migration of females, during their pregnancy and during the males’ sperm production. She will follow the bats all the way to Poland and measure similar parameters of newly pregnant bats.

Lara is expecting to start the first phase of her project soon. Today, she is joining Klaus for monitoring, as the first signs of spring are already showing up. In places like Mainau, bat boxes have been installed for many years, and Klaus knows about all the boxes and their locations.

Lara told me she has gained a lot of insight about the place and the local population of bats after joining Klaus on his monthly monitoring excursions. The relatively stable population of bats makes this place an ideal field site for Lara, as she knows that she can find bats here for her study. They are likely to return to the same site year after year, which is ideal for long-term studies on the migration behaviour of bats. 

There are about 30 boxes and it might take at least one hour to check them all. Bats usually live in larger groups, and during hibernation, another strategy they use to regulate body temperature and water loss is to cuddle up in their bat boxes in large numbers.

During winter, one might find 70 to 80 bats cramped up in one of the larger bat boxes. It is normal to open a box and see bats hanging in every corner, holding onto each other.

Lara is smiling


The easiest way to know if hibernation is over or not is to infer if the bats have started foraging. During hibernation, the bats do not venture out on a daily basis, but only when weather conditions are good.

However, as the temperatures start rising, the availability of food increases and they start waking up and foraging on a daily basis. This means they venture out for food from time to time, and use daily torpor for energy management.

How to know if they have been going out for foraging? One way is to check their weight. We know that they lose weight during winter and we know their average weight. Therefore, simply by measuring the weight of the animal, we can tell if it has started eating or not. This requires disturbing the animal.

Another trick is to observe the concentration of bats in different boxes. If they have distributed themselves in many boxes, it would indicate that they are less reliant on each other to regulate their body temperature and water loss.

Lara is explaining all these details while we move from one tree to another, checking each box along our path. We have divided into two teams; Klaus is leading one and Lara is leading another.

I am trying to avoid disturbing the process while observing other animals around us. We are finding one or two bats in different boxes, which means that maybe they have started venturing out for foraging. We quickly weigh two of them to verify our doubt; 30 grams, says the scale.

Lara is smiling as she carefully puts the bats back in their box. She is happy, as the weight is a good indication that the bats have started foraging for insects. This means that soon she will have to start doing her experiments.

In one of the boxes, we find a dead bat hanging from the wall, which we remove to take with us. Klaus tells me that finding a bat stuck in the door sometimes occurs, which is definitely an accident. However, everything one finds in the field is important. A dead animal is valuable for various other studies, such as DNA sampling, tissue sampling or specimen collection for museums. Data collection is an important part of our research.

Citizen science


It is worth mentioning the enthusiasm of the staff at Mainau. It is always exciting to be around in the early morning, when people are preparing to start their work.

The gardeners at Mainau are trying to complete maintenance before the park opens for visitors. Some of them stop us and inquire about the boxes. One of them thought we were monitoring birds, and asked us why starlings had not hatched babies during the previous year in a nest near his house. He mentioned that every other year, he has seen a couple of birds with chicks. He was worried that perhaps something was wrong. We told him that this does happen from time to time, and we were not after the starlings this morning.

Many staffers know Klaus since he has been working with the bat monitoring program for a while. He is a retired person dedicating his time for personal joy and science.

Citizens like him provide valuable aid to researchers at the cost of their personal time. It is called citizen science these days, when citizens are asked to help scientists with collecting data. This can involve identifying images of animals on a website like Zooniverse, tagging your cat with a GPS collar on Cattracker, or just taking pictures of plants, birds or insects for iNaturalist.

It is important to recognize these citizens’ contribution to science and laud their enthusiasm. These activities bring people closer to nature and understanding the world around them. If not purely for the science, these activities are done for the sheer joy of discovering the fascinating secrets of life on Earth. 

Read more about scientific research involving bats by visiting SCIENCE OUTREACH: An evening with bats»


All images courtesy Hemal Naik