The neurophysiology of sleep-swimming in mallard ducks

• Applicant: Andrea Ferretti, Ph.D.
• Subject Area: Sensory and Behavioural Biology ; Cognitive, Systems and Behavioural Neurobiology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 556238179

Sleep is a fundamental yet enigmatic behavior among animals. However, it poses a unique challenge for animals that face periods in which the need to sleep is just as important as the need to move. To mitigate this conflict, a unique state in which one brain hemisphere is awake while the other sleeps has evolved in some taxonomic groups. For instance, dolphins and fur seals utilize unihemispheric sleep to swim and maintain vigilance against predators while partially asleep. While birds also exhibit unihemispheric sleep, it remains uncertain if they can sleep while actively moving their limbs. Indeed, the only documented instance of birds displaying sleep during locomotion involves frigatebirds, which are able to nap during passive flight modes - soaring and gliding. However, sleep never occurred during flapping flight. Given the technical challenges of studying sleep during active flight, we used an alternative approach to investigate whether birds can sleep while engaging in active locomotion. This approach was inspired by field observations of geese swimming with at least one eye closed. In my recent project, Canada geese were observed sleeping while swimming, a behavior previously undocumented in birds. Geese displayed both behavioral and physiological signs of sleep while actively paddling. Interestingly, paddling could occur with one or both eyes closed. Further investigation revealed a relationship between swimming duration and the occurrence of sleep-swimming, with an initial increase followed by stabilization. Sleep-swimming might have ecological significance, compensating for the inability to sleep onshore due to disturbance from predators. During flock movements, it might also enable individuals with a greater need for sleep to stay with the group while still obtaining some sleep. While sleep-swimming is intriguing, there's much more to understand about its complexities, ecological context, and physiological mechanisms. In the proposed research project, I aim to explore 1) whether sleep-swimming occurs in waterfowl other than Canada geese; 2) if and how sleep-swimming is affected by sleep pressure and workload; 3) the link between eye closure and sleep-related brain activity.

• DFG Programme: Research Grants