Carrion Crows
Yes, I have seen them perched on paling posts-
Brooding with evil eyes upon the road,
Their black wings hooded- and they left these roosts
When I have hissed at them. Away they strode
Clapping their wings in a man's stride, away
Over the fields. And I have seen them feast
On swollen carrion in the broad eye of day,
Pestered by flies, and yet they never ceased.
But I have seen them emperors of the sky,
Balancing gracefully in the wind's drive
With their broad sails just shifting, or again
Throwing huge shadows from the sun's eye
To brush so swiftly over the field's plain,
And winnowing the air like beauty come alive.
To whom or what does the pronoun "them" in line 1 refer?