WATLAS: high throughput and real-time tracking of many small birds in the Dutch Wadden Sea

Movement is a fundamental aspect of life and tracking wild animals under natural conditions has become central to animal behaviour, ecology, and conservation science. Data from tracked animals have provided novel scientific insights on extreme migratory journeys, mechanisms of navigation, space use, and early warning signals of environmental change. Technological advancements, and chiefly the development of GPS tags, have enabled animal tracking at high spatiotemporal resolution, yet trade-offs between sampling frequency, tag weight and data retrieval limit the use of GPS tags to relatively few individuals and large species. A new 9reverse-GPS9 wildlife tracking system, called ATLAS, employs small low-cost tags, enabling simultaneous tracking of several hundred individuals at high accuracy and in real time, hence providing opportunities for studying inter-individual interactions and collective behaviour in the wild. Within an array of receiver stations, positions are calculated based on differences in tag-signal arrival times at minimally three receiver stations. Tags cost approximately 25 euro each and weigh as little as 0.6 g (without battery and coating). In this study, we introduce the Wadden Sea ATLAS system (WATLAS), implemented in the Dutch Wadden Sea, the Netherland9s only natural UNESCO World Heritage Site, yet affected by a suit of anthropogenic activities, such as fisheries, mining, shipping, and sea level rise. From July 2017 to July 2021, we tracked 821 red knots, 182 sanderlings, 33 bar-tailed godwits, and 6 common terns. With four examples, we illustrate how WATLAS opens-up possibilities for studying space-use, among-individual variation in movement, and intra-specific interactions, and inter-specific (community) space use in the wild. We additionally argue that WATLAS could provide a tool for impact assessment, and thus aid nature conservation and management of the globally important Wadden Sea ecosystem.