Wintering Barnacle Geese Exhibit an Increased Behavioural Drive for Sleep After Sleep Deprivation Without a Clear EEG-Based Sleep Rebound.

Sleep is essential for normal physiological functioning, and sleep deprivation is typically compensated by increasing subsequent sleep duration and/or intensity. However, a recent study showed that barnacle geese (Branta leucopsis) exhibit seasonal variation in sleep homeostasis, with full recovery of sleep after sleep deprivation in summer but no sleep rebound after similar deprivation in winter based on electroencephalography (EEG). This lack of sleep rebound could suggest that geese in winter do not build up sleep pressure during wakefulness or that accumulated sleep need is not reflected in EEG-based sleep measures. The current study investigated whether geese in winter accumulate sleep pressure during extended wakefulness, using behavioural activity and reactivity to stimulation as alternative indicators of sleep drive. If sleep deprivation increases sleep pressure, we expected geese to adopt more sleep postures and show elevated arousal thresholds in response to stimulation. Fifteen barnacle geese were implanted with epidural electrodes for EEG recordings and housed in a semi-natural enclosure during winter. We carefully observed and approached the geese at 10-min intervals during the night for 8-h following sunset. Although sleep was suppressed during this period, it did not lead to significant EEG changes and most of the lost sleep was not recovered. However, the behavioural observations revealed that geese exhibited increased sleep postures and diminished responsiveness to being approached. Our findings suggest that prolonged wakefulness in barnacle geese increases behavioural indicators of sleep pressure, also in winter, even though this rise in sleep drive is not clearly reflected in EEG-based sleep measures.