Tactile arousal threshold of sleeping king penguins in a breeding colony
G . DEWASMES and F . TELLIEZ
J. Sleep Res. (2000) 9, 255-259
The tactile arousal threshold of sleeping birds has not been investigated to 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 the breeding colony of Baie du Marin (Crozet Archipelago). Increasing weights were put onto one of the feet or the upper back of individuals that had been sleeping for more than 5 min until they showed behavioural signs of arousal (head raising). The weight applied to the upper back that was needed to awaken a sleeper (837 ±73 g) was 20 times greater than that applied to a foot (38 ±6 g). In terms of pressure, the dierence remained five times higher for the back (209 ±18 g/cm2) than the foot (40 g ±7 g/cm2). 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 viewed as an adaptation against progeny predation. Sleepers are frequently bumped by conspecifics walking through the colony. The increased arousal threshold associated with tactile stimulation of the back may help to preserve sleep continuity under these conditions.
HT Improbable Research.
Online experimentation available via a simulation, poke the penguin, at tur own risk 
And take care, non sleeping penguins may be more violent then sleeping ones! But at the time the paper was published that was a mere hypothesis. I hope they gathered the necessary data to ask this one.
