[EBB Sightings] birds' clocks

I have a question about birds' inner clocks.  Over the
past two and a half months a large flock of
band-tailed pigeons has been gathering in my persimmon
tree.  They feed for a while, move to an adjacent
pine, and eventually disperse.  What seems odd to me
is that they always arrive at 6:20 pm.  I would have
thought that they would be on sun time, and that as
the days became longer they would be arriving later to
perform their evening routine. Can anyone shed some
light on this?  
Thanks,
DuBose Forrest
Lafayette

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