It is interesting that nature itself seems to try to conspire against Nat's attempts to dispose of the corpses of the birds with his man-like logic, perhaps indicating the larger conflict between nature and man at play in this terrifying short story. Note the reference to the intense cold that Nat experiences when he goes to the beach and the way it is described as being colder than he had ever known. The description of what happens follows:
He crunched his way over the shingle to the softer sand and then, his back to the wind, ground a pit in the sand with his heel. He meant to drop the birds into it, but as he opened up the sack the force of the wind carried them, lifted them, as though in flight again, and they were blown away from him along the beach, tossed like feathers, spread and scattered, the bodies of the fity frozen birds. There was something ugly in the sight.
Note the way in which nature temporarily resurrects the corpses of the birds, giving them flight once more throught he wind, which could perhaps foreshadow the relentless way that the birds attack the humans in spite of the high cost in terms of their lives. Either way, Nat finds something abhorrent in the sight, indicating the unnatural way in which the birds have behaved.