Automated proximity sensing in small vertebrates: design of miniaturized sensor nodes and first field tests in bats

Abstract

Social evolution has led to a stunning diversity of complex social behavior, in particular in vertebrate taxa. Thorough documentation of social interactions is crucial to study the causes and consequences of sociality in gregarious animals. Wireless digital transceivers represent a promising tool to revolutionize data collection for the study of social interactions in terms of the degree of automation, data quantity, and quality. Unfortunately, devices for automated proximity sensing via direct communication among animal‐borne sensors are usually heavy and do not allow for the investigation of small animal species, which represent the majority of avian and mammalian taxa. We present a lightweight animal‐borne sensor node that is built from commercially available components and uses a sophisticated scheme for energy‐efficient communication, with high sampling rates at relatively low power consumption. We demonstrate the basic functionality of the sensor node under laboratory conditions and its applicability for the study of social interactions among free‐ranging animals. The first field tests were performed on two species of bats in temperate and tropical ecosystems. At <2 g, this sensor node is light enough to observe a broad spectrum of taxa including small vertebrates. Given our specifications, the system was especially sensitive to changes in distance within the short range (up to a distance of 4 m between tags). High spatial resolution at short distances enables the evaluation of interactions among individuals at a fine scale and the investigation of close contacts. This technology opens new avenues of research, allowing detailed investigation of events associated with social contact, such as mating behavior, pathogen transmission, social learning, and resource sharing. Social behavior that is not easily observed becomes observable, for example, in animals living in burrows or in nocturnal animals. A switch from traditional methods to the application of digital transceiver chips in proximity sensing offers numerous advantages in addition to an enormous increase in data quality and quantity. For future applications, the platform allows for the integration of additional sensors that may collect physiological or environmental data. Such information complements social network studies and may allow for a deeper understanding of animal ecology and social behavior.

Estimating interactions between individuals from concurrent animal movements

“…Recent technological advances enable us to observe movement paths of a large range of species at temporal and spatial scales that are suitable for studying fine-scale attraction and avoidance behaviours towards others (Kays, Crofoot, Jetz, & Wikelski, 2015;Vanak et al, 2013). While tracking multiple individuals simultaneously is difficult with hand-held VHF methods (but see Schülke & Kappeler, 2003) and still relatively expensive with GPS (due to the costs of single GPS units), this becomes both easier and cheaper (price per tag) with next-generation systems, for example wireless sensor networks, which can include proximity loggers (Mennill et al, 2012;Ripperger et al, 2016), or local high-throughput telemetry systems such as ARTS (Automated Radio-Telemetry Systems; Kays et al, 2011) or ATLAS (Advanced Tracking and Localization of Animals in real-life Systems; Weiser et al, 2016). Thus, we expect multi-individual, multi-species movement data to become more readily available in the near future.…”

Thinking small: next-generation sensor networks close the size gap in vertebrate biologging

“…In addition, every meeting is labeled with a maximum signal strength intensity indicator (RSSI). This makes it possible to subset the meeting dataset according to signal strength, an estimate for proximity 13 . RSSI values can distinguish close-contact associations from associations based on merely occupying the same area.…”

Proximity sensors reveal social information transfer in maternity colonies of Common noctule bats

“…Whenever one or more tracking sensors are within reception range of ca. 10 m maximum distance (Ripperger et al 2016), a so called ‘meeting’ is created. As soon as no signal has been received by the respective meeting partner for five sending intervals (corresponding to 10 seconds), the meeting is closed and stored to on-board memory along with the ID of the meeting partner, a timestamp, total meeting duration, and a maximum signal strength indicator (RSSI) of the meeting.…”

“…We used a refined version of miniaturized proximity sensors, which has been described and tested in free-ranging bats first in Ripperger et al (2016). The proximity sensor comprises a System-on-Chip (SoC) for communication control and on-board data processing, a transceiver which enables communication in the 868MHz frequency band with other proximity sensors or base stations and a wake-up-receiver which activates full system functionality from an energy-saving low-power mode whenever communication partners are in range.…”