On October 4, 2018, I went out with Javi (Dr. Javier Lázaro Tapia) to catch some hedgehogs. He is a postdoc in Dechmann Lab at the Max Planck Institute of Ornithology. I work at this Institute where everyone is passionate about wildlife and many are keen to share their knowledge with others.

Javi is one such scientist, and in his own words, he is becoming an expert on insectivores. He has previously worked with shrews, and his current project involves studying hedgehogs. In the near future, he wants to study moles. This article is about one evening of Javi’s work.

Being a wildlife researcher involves wearing many different hats. In the morning, you can find Javi quietly sitting behind a computer in his office at the Institute. He is doing data analysis for his research, planning for the next publication or checking out applications for grants.

In the evening, he has his own plans. Going home early is not his priority today. It’s his field day, and that means he has to go out and catch hedgehogs for his study. Frodo—a close ally and possible co-author for the next publication—waits for him in the parking lot.

Frodo is a friendly dog who is Javi’s true companion. They play together, live together and occasionally work together. Yes, Frodo goes with Javi on some of his field excursions and helps him track down animals.

Why study hedgehogs?

It’s evening time and it is getting cold in Radolfzell [Germany]. I receive a message to be at the meeting spot in 20 minutes. Javi is already preparing for today’s field task: recapturing hedgehogs. The kit involves a radio signal receiver, an antenna, extra batteries, treats for Frodo and a box for safely installing the hedgehogs.

Today, Javi has three additional companions, all interested in knowing more about his work and the process. The plan is to go and replace the batteries in one of the stationary antennas, then try to catch two hedgehogs near the Institute.

The hedgehogs have radio tags fitted on their backs, and we use the signals to recapture them. Javi has previously caught them and implanted biologging sensors in their bodies to measure their heartbeat and body temperature data. 

So why is Javi studying hedgehogs? He wants to discover how different animals have adapted to survive changes in weather patterns. In Europe, winters can be cold, and many places experience temperatures ranging from 0 to -20 degrees Celsius in winter and +20 to 30 degrees Celsius during summer.

Many animals migrate to warmer climates to avoid the bitter cold; for instance, birds go from Europe to Asia and Africa. Warm-blooded animals need to maintain their body temperature, and in order to do this, they have to generate enough energy and consume food to produce this energy.

A consistent food supply is crucial to maintaining body temperature during winter. However, winter means a scarcity of food for herbivores and insect eaters. In winter, food resources are reduced and this forces animals to adapt their behaviour. The change of seasons shapes an animal’s lifestyle and behaviour.

Many animals do not migrate and stay in the same place. These animals have evolved to deal with temperature changes and resource shortages. For example, some animals enter a state called ‘hibernation’ or ‘torpor,’ which means reduced activity.

The animal’s body temperature comes down, but critical organs do not stop. At the same time, they conserve energy by temporarily stopping their movement and some biological processes. This way, they require a minimum amount of energy to live and survive the winter.

In this period, they do not move and can stay in one place for weeks or months. This is the case with hedgehogs. They lower their body temperature from 36 to 5 degrees Celsius, and can stay inactive in winter for up to two to three weeks and then move a little bit, or change to a different hole and hibernate again.

We do not know exactly why hedgehogs move between hibernation phases, and it is this remarkable transition that fascinates Javi.

Tracking the animals

We make our way uphill from the Institute and reach a spot in the field. Javi removes batteries from his bag and goes into the bushes to replace the batteries in a stationary antenna hidden near the highest point on the hill.

The antenna looks like those old-school TV signal receivers, once seen on every roof, that have been replaced by elegant-looking satellite dishes. This antenna records the radio signal coming from hedgehogs; it fluctuates if the hedgehog is moving, and is stable if the hedgehog is stationary. For example, if Frodo is moving and barking, his volume will change in intensity depending on his distance, but the volume intensity will be constant if he stops moving.

This information helps Javi find sequences when hedgehogs are moving or remain stationary, and it’s useful to combine movement with heart rate and body temperature information in order to study hibernation.

The antenna is constantly capturing data about hedgehog movements. We quickly replace the batteries while keeping a safe distance from a big wasp nest—working with wildlife involves being cautious at all times.

This antenna is capable of receiving multiple signals at the same time, and it’s ideal to place one in the area where multiple individuals equipped with radio transmitters are living. We also have a handheld receiver that has antennae attached to it. It is mobile, and tuned to the frequency of the transmitter on individual hedgehogs.

The stationary antenna is bigger and therefore can listen to very faint signals. The handheld, on the other hand, is dependent on the quality of signal and type of antenna, and is a great device to use to catch the animals. However, if you are not in the right area, you will not get any signal. Luckily, hedgehogs do not go far from their range and Javi is confident of finding a signal in the neighbourhood.

Javi is Spanish and does not speak fluent German. He says we might have to do some explaining if some people stop us on the way, especially if the hedgehog decides to visit someone’s garden. It would be a good idea to explain what four foreigners are doing in their garden with a strange-looking antenna.

I decide to take the lead if this situation happens, but we are confident of not running into any problems, as the Institute has been here for more than 50 years and people are friendly to researchers.

We go down the hill and start listening for our first hedgehog. Javi tunes the tracker to the required frequency, waving the antenna in all four directions, and decides to walk towards the Institute. We lose the signal, stop for a while and change direction again.

The signal is a small beep sound, while the display of the receiver shows a strength similar to the signal bars for mobile phone coverage. We are puzzled and we look at Javi. He is equally puzzled and decides to walk towards the hill.

Frodo is having his own time in the field, sometimes finding something interesting but then coming back to us.

Catching a hedgehog

We move back towards dense bushes near an apple tree. The signal gets stronger and stronger. Javi replaces the antenna with a smaller antenna to see if this antenna also picks up the signal. If it does, then the animal is much closer. This is a simple trick to narrow down the distance of animals.

This work involves getting into uncomfortable positions, and dirt is your friend while doing fieldwork.

Larger antennae have a range of tens of metres, while small antennae have a range of only a few metres. Javi takes out his gloves, as it looks as though he will have to go into the bushes. Yes, this work involves getting into uncomfortable positions, and dirt is your friend while doing fieldwork.

Suddenly, Frodo springs into action and goes into the bushes. He has learned to find hedgehogs and point them out to Javi. The hedgehogs, when frightened (AKA ‘stunned’), usually become a small spiny ball whenever any animal approaches them. This is their survival strategy against predators in natural encounters, and they treat humans and dogs similarly.

Once a hedgehog turns on its defense, it will not become active until it is sure that the danger has passed. Frodo’s appearance stuns the hedgehog and it curls itself into a ball, making it easier to find i in the undergrowth. I remove Frodo, who wins a treat from Javi, and the hedgehog goes into its temporary box.

A different hedgehog for each study

Javi shows us the markers he has put on some of the spines. The markers have a unique identification code (yellow tape and an image) so we can identify the animal if it’s caught again and release it into the wild. He is not allowed to use the same animal twice for his studies.

He shows us the radio tag attached to some of the spines at the back end of the hedgehog. Identification also helps when a radio tag is lost; if the animal is trapped again, then the implant that measures heart rate and temperature is promptly removed.

Javi records the time and location of capture of this particular hedgehog in his diary, and makes notes about battery replacement. Detailed logs and all required data are recorded over long field studies. Hedgehogs have a very different system for dealing with winter, and Javi is excited about removing the implant from this individual and releasing it back into the wild a few days later. The minor surgery to remove the implanted sensor will be performed by the vet at the Institute.

We take a moment to enjoy the autumn sunset. The golden shade of sunlight is any photographer’s dream. The fields, the apple trees and the sounds of good radio signals make us happy. We return to the Institute to grab the box for the next hedgehog.

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