[cobirds] Bushtit question

A small flock of bushtits visited our yard yesterday. It was just 5F.  When not feeding, they huddled closely together to keep warm, at times in regular head-tail-head-tail order  (https://ebird.org/checklist/S103608720). 

I could not detect if there was a pecking order and wonder if they rotate through the position on the outside, taking turns. If so, is it the weakest who are on the outside, losing the competition for the warmest spots on the inside?  Or is it the strongest on the outside, protecting weaker ones on the inside? Older birds outcompeting younger ones? Families or pairs in the center and left-over singles on the outside? Females seemed to be more often on the outside. Or is it all just random, first come, first served?

Anyone who can shed light on this?

Willem

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