Central-place foragers returning to their colony can rely on various environmental cues—such as landmarks or the sun angle—to adjust their return movement behaviour and navigate efficiently. While these homing strategies have been well documented in temperate environments, it remained unclear until recently whether tropical seabirds nesting on low-lying coral reef atolls could navigate with similar efficiency, and whether they might rely on the time of day to time their return journeys.
To address this question, this study explored the navigation behaviour of 207 breeding adult Red-footed Boobies, Sula sula rubripes, from four colonies across the Chagos Archipelago, central Indian Ocean, equipped with archival GPS loggers between 2016 and 2023.
Red-footed Booby flying in the Chagos Archipelago ©Nathan Hudson-Peacock
To investigate their homing behaviour, a Hidden Markov Model was used to assign behavioural states—resting, foraging, and transiting—to Red-footed Boobies’ GPS tracks. The homing path was defined as the segment between the last foraging location and the bird’s return to the colony. Then movement metrics from these return trips were modelled in relation to time of day and distance to the colony to determine whether the birds adjust their homing behaviour to ensure arrival before dusk.
Example of 120 s interpolated tracks from two Red-footed Boobies showing at-sea movement behaviour. A 10 km buffer around the Diego Garcia colony (red dashed line) was used to select the final foraging locations (red circle). The last dive location (blue circle), direction of travel (black arrows) and waters shallower than 100 m (light-blue shaded areas) are shown. (Figure 1a from Coste et al. 2025)
The results showed that Red-footed Boobies navigate efficiently back to their colonies on fast, straight, and direct flights—even in visually sparse environments with few prominent landmarks. Notably, this study provides evidence that these birds are able to adjust their homing behaviour according to the time of day, likely using solar and visual cues to ensure timely return. The closer to the evening twilight they start their homing journey, the shorter, faster, and more direct their routes become. At the onset of their return, Red-footed Boobies appear capable of assessing both their distance from the colony via their vision and the time of day from solar angles, possibly using a time-compensated sun compass. This allows them to estimate how much time remains before dusk and to adjust their behaviour accordingly. Such time- and energy-efficient homing strategies may help optimise energy expenditure during central-place foraging trips, which could be especially advantageous in tropical marine environments, where food resources are often more patchily distributed and less abundant than in temperate or polar regions.
Trip timing adjustment of 207 Red-footed Boobies from four colonies in the Chagos Archipelago (N = 422 trips). (a) Homing duration decreases as dusk approached. (b) Homing birds become fast as dusk approached. (c) Homing path becomes straighter as dusk approached. The red line (with 95% CI) indicates the predicted estimates extracted from the respective linear mixed models. The black dashed line is dusk time. Coloured shading indicates beeline distances. (Figure 2. from Coste et al. 2025).
These findings shed new light on how tropical seabirds navigate vast oceanic environments, revealing the remarkable adaptability of their homing strategies. As threats such as bycatch, habitat degradation, and climate change continue to intensify, understanding the movement ecology of seabirds is more critical than ever. Studying how and when they return to their colonies not only deepens our knowledge of their behaviour, but also informs conservation strategies aimed at protecting population connectivity and reproductive success in an increasingly human-altered seascape.