Recent advances in animal tracking technology have ushered in a new era in biologging. However, the considerable size of many sophisticated biologging devices restricts their application to larger animals, whereas older techniques often still represent the state-of-the-art for studying small vertebrates. In industrial applications, low-power wireless sensor networks (WSNs) fulfill requirements similar to those needed to monitor animal behavior at high resolution and at low tag mass. We developed a wireless biologging network (WBN), which enables simultaneous direct proximity sensing, high-resolution tracking, and long-range remote data download at tag masses of 1 to 2 g. Deployments to study wild bats created social networks and flight trajectories of unprecedented quality. Our developments highlight the vast capabilities of WBNs and their potential to close an important gap in biologging: fully automated tracking and proximity sensing of small animals, even in closed habitats, at high spatial and temporal resolution.

Female bats of temperate zones often communally rear their young, which creates ideal conditions for naive juveniles to find or learn about resources via informed adults. However, studying social information transfer in elusive and small-bodied animals in the wild is difficult with traditional tracking techniques. We used a novel ‘next-generation’ proximity sensor system (BATS) to investigate if and how juvenile bats use social information in acquiring access to two crucial resources: suitable roosts and food patches. By tracking juvenile–adult associations during roost switching and foraging, we found evidence for mother-to-offspring information transfer while switching roosts but not during foraging. Spatial and temporal patterns of encounters suggested that mothers guided juveniles between the juvenile and the target roost. This roost-switching behaviour provides evidence for maternal guidance in bats, a form of maternal care that has long been assumed, but never documented. We did not find evidence that mothers guide the offspring to foraging sites. Foraging bats reported brief infrequent meetings with other tagged bats that were best explained by local enhancement. Our study illustrates how this recent advance in automated biologging provides researchers with new insights into longstanding questions in behavioural biology.

In this paper, the BATS project is presented, which aims to track the behavior of bats via an ultra-low power wireless sensor network. An overview about the whole project and its parts like sensor node design, tracking grid and software infrastructure is given and the evaluation of the project is shown. The BATS project includes a lightweight sensor node that is attached to bats and combines multiple features. Communication among sensor nodes allows tracking of bat encounters. Flight trajectories of individual tagged bats can be recorded at high spatial and temporal resolution by a ground node grid. To increase the communication range, the BATS project implemented a long-range telemetry system to still receive sensor data outside the standard ground node network. The whole system is designed with the common goal of ultra-low energy consumption while still maintaining optimal measurement results. To this end, the system is designed in a flexible way and is able to adapt its functionality according to the current situation. In this way, it uses the energy available on the sensor node as efficient as possible.

In this letter a low weight and low power non-invasive ECG heart beat detector for pulse analysis in small vertebrates is proposed and verified on bats. To achieve this low weight the ECG frontend is optimized for low space requirements and low energy consumption, drawing only 30 μA. The complete system including the system on chip for recording and wireless data transmission requires 3.3 mA in active mode. Since only a small battery with a weight of 0.6 g is used, this low power consumption is necessary to still being able to reach a continuous measurement time of more than 6 h. Compared to other solutions this newly proposed system gathers data via non-invasive electrodes while still achieving a high signal quality and at the same time is light enough to allow airborne measurements without affecting the animals behavior.

In wireless sensor networks, it can be important to determine the distance of sensor nodes between each other. At the same time, many applications have strict requirements on the weight and size of a sensor node. For example, animal monitoring requires low weight and size to minimize the impact on the animal. A distance estimator based on the received signal strength indicator (RSSI) in combination with free-space loss can efficiently be implemented but is prone to errors and inaccuracy, especially when using antennas with high directivity. In this article, a new approach using two separate antennas in two different frequency bands on ultrasmall systems is proposed. It is shown how the antenna gain directivity can be compensated. In this way, a more precise measurement of the free-space loss, and thus of the distance between the nodes, becomes possible.