I checked back with Avian Haven today and the great Black Hawk had its first meal and ate with gusto, they said.  Still too early to know about the frostbitten feet but they promise more tomorrow.

Proof positive if you've ever wondered if wild birds and animals suffer in these extreme temperatures.
This poor Great Black Hawk was taken to Avian Haven struggling with frostbite in both feet. Avian Haven is located in Freedom Maine and I have taken several birds to them over the years. They are amazing rehabilitators and he/she couldn't be in better hands.

Found by a man named  Alfredo Nicholas in Deering Oaks Park in Portland the hawk was rescued and is now in stable condition. Avian Haven assures that the extent of its recovery will be the determining factor in its re-release in the future and that those decisions will be made in consultation with Maine Department of Inland Fisheries & Wildlife and US F&W Service..  Meanwhile Avian Haven is doing a great job keeping their Facebook page updated with its progress.

Also if you wish to support this non-profit here is the link.