Tactile arousal threshold of sleeping king penguins in a breeding colony

The tactile arousal threshold of sleeping birds has not been investigated t o date. In this study, the characteristics of this threshold were assessed by stimulating either the upper back or a foot of two groups (one cutaneous site per group) of 60 sleeping king penguins (Aptenodytes patagonica) in t he breeding colony of Baie du Marin (Crozet Archipelago). Increasing weight s were put onto one of the feet or the upper back of individuals that had b een sleeping for more than 5 min until they showed behavioural signs of aro usal (head raising). The weight applied to the upper back that was needed t o awaken a sleeper (837 +/- 73 g) was 20 times greater than that applied to a foot (38 +/- 6 g). In terms of pressure, the difference remained five ti mes higher for the back (209 +/- 18 g/cm(2)) than the foot (40 g +/- 7 g/cm (2)). Because the king penguin incubates its single egg and rears its young chick on its feet, the low threshold measured at this level could be viewe d as an adaptation against progeny predation. Sleepers are frequently bumpe d by conspecifics walking through the colony. The increased arousal thresho ld associated with tactile stimulation of the back may help to preserve sle ep continuity under these conditions.