Whether bats, small birds or even butterflies: For many small and light animals, it has so far been difficult to understand behavior and movements using sensors or GPS location. Now researchers have developed a method that enables this biologging even for such light weights. The system works through a combination of particularly light sensors and receiving antennas, which are set up in a wide area around the study area.
When it comes to researching animal movements and behavior, biologists are the method of choice. Using such sensors or GPS transmitters attached to animals, biologists have obtained valuable data on the diving and migrating behavior of whales and other marine mammals, for example, but have also accompanied migratory birds on their flights.
Combination of mini-loggers and stationary receivers
But in order to collect this data and transmit it to satellites or the researchers, such biologgers need relatively large and heavy batteries. For very small animals, these sensor or GPS backpacks are often too heavy. In addition, the GPS location is often not precise enough for field observation on a smaller spatial scale. “In addition, satellite reception in complex habitats such as dense forests is often impaired and even completely impossible if the animals are in hollow trees, caves or underground passages,” Simon explains
Ripperger from the Museum für Naturkunde Berlin and his colleagues. A suitable logging method has so far been lacking, especially for bats and small mammals.
A new biologging system that Ripperger and his colleagues have developed and tested on bats can now help. The system uses a combination of stationary receivers and animal biologists. The biologists only weigh one to two grams and can collect and send data for several weeks. An algorithm ensures that the data does not have to be continuously transmitted, but is instead sent in batches to the receiving stations. This limits the energy consumption of the logger to a minimum and allows you to keep your batteries extremely small and light.
Successful in tests with bats
Ripperger and his team tested how well the new Biologger system works and how many receiving stations are needed to locate the animals precisely enough in three bat species. These flight mammals are small and move quickly through often dense vegetation, which has been a great challenge for logging methods that have been common until now. In the first field trial, the researchers equipped 50 vampire bats (Desodus rotundus) with the new biologists in order to capture their social networks. For this purpose, the sensors registered every two seconds whether and how close another sensor was present in their environment. “In this way, we recorded almost 400,000 individual meetings in the first eight days of our test,” the scientists report. “Our system created a complete network of spatial proximity every few seconds.”
In a second field trial in a deciduous forest in Bavaria, the researchers investigated how many receiving stations are required to obtain sufficiently precise information about the position of mouse-eared bats (Myotis myotis). It turned out that, with 15 to 17 nodes, the position could be located within a good five meters despite the dense tree population – this was even more precise than the GPS trackers tested for comparison purposes, as Ripperger and his team report. And in an area of around 1.5 hectares, even eleven receiving stations were sufficient to achieve a location. In the third test, the researchers wanted to know how well the data could be transmitted over longer distances of up to four kilometers. Large noctule (Nyctalus noctula) in a forest in Berlin served as test objects. The new biologgers also proved to be suitable in this experiment.
“Our new, innovative sensor system takes biologging to a new level,” says Ripperger. “We can record where animals move and how they interact much more precisely than with conventional technology.” Next, the researchers want to use their new biologging system to record the habitat use of sand lizards (Lacerta agilis) along train tracks in Germany. Further studies could focus on rodents, songbirds, or even large insects such as stag beetles, large hay horses, or skull swarmers.
Source: Museum of Natural History – Leibniz Institute for Evolution and Biodiversity Research; Technical article: PLoS Biology, doi: 10.1371 / journal.pbio.3000655