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Recent technological advances have multiplied the variety of biologgers used in wildlife research, particularly with small-bodied animals. Passive integrated transponders (PIT) have been used for decades to log visits of tagged animals at reader-equipped artificial feeders or roost boxes. More recently, novel miniaturized sensor nodes can collect data on social encounters among tagged individuals in any location. Combining these systems allows researchers to gather high-resolution tracking data on certain individuals from their long-term PIT-tagged animal populations. However, there can be a risk of interference among tracking systems. Here we tested whether placing an additional biologging sensor on top of a PIT tag might attenuate the magnetic field reaching the PIT tag and, in turn, hamper reading success of the radio-frequency identification (RFID) reader. We also evaluated data transmission by a digital sensor node in the presence of a magnetic field created by the RFID antenna. The combination of this RFID system and wireless biologging sensors works without error, suggesting that the simultaneous use of PIT tags and other digital biologgers, e.g., miniaturized GPS-loggers, should also work together properly when communication channels do not overlap. The combination of long-term monitoring with PIT tags and short-term tracking with biologging sensor nodes creates exciting new opportunities to gather rich social data when individuals are not present at RFID reader stations.

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.

In this letter, a low-weight and low-power noninvasive ECG heart beat detector for pulse analysis in small vertebrates is proposed and verified on bats. To achieve this low weight, the ECG front end is optimized for low space requirements and low energy consumption, drawing only 30 $\mu$ A. 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 be able to reach a continuous measurement time of more than 6 h. Compared to other solutions, this newly proposed system gathers data via noninvasive electrodes while still achieving a high signal quality and, at the same time, is light enough to allow airborne measurements without affecting the animal's behavior.

This paper gives an overview of the BATS project, which aims to track the behavior of bats by developing an ultra-low power wireless sensor network. It is composed of an ultra-low weight sensor node that is attached to the animal and extensive ground infrastructure for tracking the animals as well as remote data download of locally stored sensor data from the tags. The system achieves its low power consumption by adaptively enabling certain functions based on the current situation. The mobile node, as a key component of the system, contains a variety of sensors, including an electrocardiogram (ECG) to allow precise insights in the animals’ behavior while maintaining a low weight of around 1 g depending on the hardware configuration.

Recent technological advances have multiplied the variety of biologgers used in wildlife research, particularly with small-bodied animals. Passive integrated transponders (PIT) have been used for decades to log visits of tagged animals at reader-equipped artificial feeders or roost boxes. More recently, novel miniaturized sensor nodes can collect data on social encounters among tagged individuals in any location. Combining these systems allows researchers to gather high-resolution tracking data on certain individuals from their long-term PIT-tagged animal populations. However, there can be a risk of interference among tracking systems. Here we tested whether placing an additional biologging sensor on top of a PIT-tag might attenuate the magnetic field reaching the PIT-tag and in turn hamper reading success of the radio-frequency identification (RFID) reader. We also evaluated data transmission by a digital sensor node in the presence of a magnetic field created by the RFID-antenna. The combination of this RFID-system and wireless biologging sensors works without error, suggesting that the simultaneous use of PIT-tags and other digital biologgers, e.g. miniaturized GPS-loggers, should also work together properly when communication channels do not overlap. The combination of long-term monitoring with PIT tags and short-term tracking with biologging sensor nodes creates exciting new opportunities to gather rich social data from individuals not present at RFID reader stations.

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., Recent advances in technology potentially allow great progress in animal tracking. This article presents a wireless biologging network (WBN) that enables simultaneous direct proximity sensing, high-resolution tracking, and long-range remote data download at tag weights of only one to two grams.

In wireless sensor networks it can be critical to determine the distance of sensor nodes towards each other. While a simple RSSI free space loss distance estimation is quick to implement, it is prone to errors and can be highly inaccurate, especially when using antennas with high directivity. In this paper a new approach for use on small systems with two antennas in two frequency bands is proposed. It is shown how the antenna gain directivity can be compensated and thus more precise measurements of the free space loss becomes possible.

In this paper an advanced sensor node for animal tracking is proposed, which includes an accelerometer, an air pressure sensor as well as an electrocardiography sensor. The system is designed for studying the physiology and behavior of bats by inferring activity, wing beat frequency as well as heart rate. This system offers outstanding functionality compared to other tracking nodes and is easily applicable thanks to its noninvasive design. Gluing the sensor to the bat's back keeps the impact on the animal at a minimum and retrieval of the animal to remove the tag is not required since the tag falls off after a few days.

In this paper a small size low power electrocardiogram (ECG) system which is optimized for the heart rate detection of bats is proposed. Due to the smaller size and different physical properties of animals like bats the system has to fulfill different requirements than standard human ECGs. The usecase of animal monitoring also requires an ultra-low power approach to enable long battery runtime. The described system has been evaluated with measurements on bats and compared to a commercially available ECG integrated circuit (IC). Apart from the ECG circuit itself the electrodes and the electrode position as well as the used algorithms are evaluated.

SummaryBats are a highly gregarious taxon suggesting that social information should be readily available for making decision. Social information transfer in maternity colonies might be a particularly efficient mechanism for naïve pups to acquire information on resources from informed adults. However, such behaviour is difficult to study in the wild, in particular in elusive and small-bodied animals such as bats.The goal of this study was to investigate the role of social information in acquiring access to two types of resources, which are crucial in the life of a juvenile bat: suitable roosting sites and fruitful feeding grounds. We hypothesized that fledging offspring will make use of social information by following informed members of the social groups to unknown roosts or foraging sites.In the present study we applied for the first time the newly developed miniaturized proximity sensor system ‘BATS’, a fully automated system for documenting associations among individual bats both while roosting and while on the wing. We quantified associations among juveniles and other group member while switching roosts and during foraging.We found clear evidence for information transfer while switching roosts, mainly among juveniles and their genetically identified mothers. Anecdotal observations suggest intentional guidance behaviour by mothers, indicated by repeated commuting flights among the pup and the target roost. Infrequent, short meetings with colony members other than the mother indicate local enhancement at foraging sites, but no intentional information transfer.Our study illustrates how advances in technology enable researchers to solve long-standing puzzles. Miniaturized proximity sensors facilitate the automated collection of continuous data sets and represent an ideal tool to gain novel insights into the sociobiology of elusive and small-bodied species.

In this paper an enhanced version of the mobile node developed in the BATS project for small sized animals like bats is proposed. The new design uses highly integrated components and a more compact design. In the paper the new design is described with focus on the conducted changes. The new design has been proven in field test in Germany from which first results are shown. Special focus is put on the power supply and mobile node runtime. For pure encounter detection a runtime of more than 420 hours has been recorded. Without any communication with other nodes the current is as little as 50 μA while still being in active mode.

Summary Social bonds, maintained by mutual investments of time and energy, have greatly influenced the evolution of social cognition and cooperation in many species [e.g., 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. However, there are two pitfalls regarding “social bonds” as an explanation for social structure and cooperation [ 1 , 9 , 10 , 11 ]. First, studies often incorrectly assume that frequent association implies partner fidelity based on mutual social preference, but even seemingly complex nonrandom interaction networks can emerge solely from habitat or spatial structure [ 12 , 13 , 14 , 15 , 16 ]. Second, the false appearance of partner fidelity can result from stable options in the “partner market” [ 1 , 9 , 10 , 11 , 17 ]. For instance, individuals might preferentially groom the same partner, even if the decision depends entirely on the immediate costs and benefits rather than relationship history. Given these issues, a key challenge has been testing the extent to which social structure is driven by the intrinsic relationship history versus the extrinsic physical and social environment. If stable bonds exist, they should persist even if the individuals are moved to a dramatically different physical and social environment. We tested this prediction by tracking social relationships among common vampire bats (Desmodus rotundus) moved from the lab to the wild. We show that allogrooming and food sharing among female vampire bats induced in captivity over 22 months predicted their assortativity and association rates when we subsequently tracked them in the wild with custom-made high-resolution proximity sensors. The persistence of many relationships across different physical and social environments suggests that social structure is caused by both extrinsic constraints and intrinsic partner fidelity.

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.