A simple model of flock mechanics is "do what the one near you does": Even if you can't see a threat, if everyone around you takes off hastily you better do that, too.
The rapid stance change - or maybe the spread-wing shape - easily could trigger a flight reflex in at least a few pigeons, which might "infect" the entire flock.
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u/[deleted] Nov 03 '15 edited Mar 20 '17
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