Chronobiological research has seen a continuous development of novel approaches and techniques to measure rhythmicity at different levels of biological organization from locomotor activity (e.g. migratory restlessness) to physiology (e.g. temperature and hormone rhythms, and relatively recently also in genes, proteins and metabolites). However, the methodological advancements in this field have been mostly and sometimes exclusively used only in indoor laboratory settings. In parallel, there has been an unprecedented and rapid improvement in our ability to track animals and their behaviour in the wild. However, while the spatial analysis of tracking data is widespread, its temporal aspect is largely unexplored. Here, we review the tools that are available or have potential to record rhythms in the wild animals with emphasis on currently overlooked approaches and monitoring systems. We then demonstrate, in three question-driven case studies, how the integration of traditional and newer approaches can help answer novel chronobiological questions in free-living animals. Finally, we highlight unresolved issues in field chronobiology that may benefit from technological development in the future. As most of the studies in the field are descriptive, the future challenge lies in applying the diverse technologies to experimental set-ups in the wild.This article is part of the themed issue 'Wild clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals'.

Centre for Animal Movement Research Department of Biology Lund University Lund 22362 Sweden

Department of Animal Ecology Netherlands Institute of Ecology PO Box 50 6700 AB Wageningen The Netherlands

Department of Animal Ecology Netherlands Institute of Ecology PO Box 50 6700 AB Wageningen The Netherlands Institute of Biodiversity Animal Health and Comparative Medicine University of Glasgow Glasgow G128QQ UK

Department of Behavioural Ecology and Evolutionary Genetics Max Planck Institute for Ornithology Seewiesen 82319 Germany NIOZ Royal Netherlands Institute for Sea Research Department of Coastal Systems Utrecht University PO Box 59 1790 AB Den Burg The Netherlands Faculty of Environmental Sciences Czech University of Life Sciences Prague Prague 16521 Czech Republic

Groningen Institute for Evolutionary Life Sciences University of Groningen Groningen 9747 AG The Netherlands

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