High‐throughput tracking reveals differences in low‐tide space use between day and night in wintering Red Knots

Within intertidal ecosystems, the availability of foraging areas for shorebirds changes rapidly with the tidal cycle, imposing a strict regime of foraging opportunity. Several shorebird species have been reported to forage during both diurnal and nocturnal low‐tide periods, making the most of available foraging times, but detailed descriptions of behaviour at night are rare. We may expect shorebirds to engage in distinct spatial behaviours between day and night due to differences in risk landscape, or because moving between foraging sites and searching for indicators of profitable foraging patches may require different strategies. Comparing the diurnal and nocturnal behaviour of the same individuals on intertidal mudflats is a challenge and requires high temporal and spatial resolution data collected over several weeks so that low‐tide periods that fall mostly in the day or in the night can be compared. We used ATLAS—a high‐throughput radiotracking system—to collect high‐resolution tracking data from Red Knots Calidris canutus , between September and October (2018–2022) in the Dutch Wadden Sea. We found that the Red Knots stayed within patches longer at night and that patches were also slightly closer (~100 m) to the roost site at low tide, and covered a smaller area per tide. Red Knots were found to use 20% of their diurnal range at night, and 41% of their nocturnal range during the day. At night, Red Knots showed higher site fidelity across tides. We suggest that these differences in behaviour are probably due to a combination of navigational capacity, risk perception and/or prey conspicuousness.