Swimming asleep: characterization, ontogenesis and energetic basis of sleep during paddling in waterfowl

Although sleep has been found in most animals, our understanding of its function remains limited. A longstanding theory proposed that sleep has energy saving functions. Thus, an individual is expected to engage in sleep more often when energy intake is much lower than its energy demand.

However, while facing such a negative energy balance, there might be some ecological contexts within which the need for sleep may conflict with the need for being awake.

To overcome this issue, some species can display a mixed state wherein one cerebral hemisphere is asleep and the other is awake.

Other than its importance as anti-predatory strategy, this phenomenon has received attention because it is the only sleep type that is compatible with locomotion, as shown in dolphins. However, in birds the possibility of combining sleep and active locomotion has never been demonstrated.

In my recent observations, I obseved several goose species paddling while keeping their eyelids closed, which is a typical feature of sleep.

The general aims of my project are to describe, for the first time in birds, the simultaneous occurrence of sleep and stereotype locomotion and to investigate how energy balance affects this phenomenon.

Using the graylag goose (Anser anser) and state-of-the-art neurophysiological recording methods, I will describe whether eye closure during paddling is actually associated with sleep and if it occurs uni- or bihemispherically. Then, I will test whether the expression of this phenomenon varies during early-life development.

Finally, I will study the modulation of such behavior in response to a gradient of energy requirement.

My findings will not only be fundamental for uncovering the existence of sleep during active locomotion in birds, as well as factors driving its occurrence, but they will also propose the use of sleepswimming in geese as a model for investigating sleepwalking in humans, a poorly understood and, in some cases, life-threatening disorder.