We went to a bonfire party tonight. There was the usual array of 'explosives' and massive fireworks going off all over the place.
One thing I noticed was that Flash (aged 17 months), was initially startled by the fireworks and then became gradually docile and quite sleepy during the display - despite the loudness of the explosions. When we got back indoors, she pepped up again and was rather alert. Earlier in the week we went to an outdoor Halloween event and Flash was alert throughout, so the only real difference was the noise of tonight's event. I recall the same thing happening with Captain Kid when she was the same age.
This got me thinking, I wonder if sleep can be invoked as a survival mechanism. I mean I understand that we are all born with two basic fears - of heights and loud noises. All other fears and phobias are apparently learned.
Thus when faced with the apparent danger of tonight's environment (loud noises), it would make sense for Flash to sleep. This, as I see it would have an individual benefit to her as she would lower her stress hormones (cortisol), and also be of advantage to the wider group as the normally noisy infant would be 'inert' and thus unable to give a vocal reference to any 'predator' of the groups' position.
Just a thought.