another phrase from a Billy Collins poem

"I saw them near dawn"
he was talking about the crew team out on the river,
I see the crows near dawn, perched high above me,
their black shiny heads bobbing up and
  down, they caw racously at one another
then fly away in black clouds
I walk next to a river, a small one late in winter, I see
the same red sleeping bag near the bank,
crumpled and dirty.
there is no one huddled inside
the bushes and trees are naked
but I can feel them waking up,
I hear the rush of their blood.