The spell/incantation that is included with the post, is from Russia, pre-1900's. It is reasonable accurate to my knowledge (my source is a book written in 1865.) however the word wolf should be substituted with the appropriate animal (..eagle?). The Russian's call the were-wolf ('thropes in general.) 'oborot' which translated as 'one transformed' thus the spell should work for all forms.
He who desires to become an oborot, let him seek in the forest a hewn-down tree; let him stab it with a small copper knife, and walk round the tree, repeating the following incantation :-
On the sea, on the ocean, on the island, on Bujan,
On the empty pasture gleams the moon, on an ashstock lying
In a green wood, in a gloomy vale.
Towards the stock wandereth a (shaggy wolf),
Horned cattle seeking for his (sharp white fangs);
But the (wolf) enters not the forest,
But the (wolf) dives not into the shadowy vale,
Moon, moon, gold-horned moon,
Check the flight of bullets, blunt the hunters' knives,
Break the shepherds' cudels,
Cast wild fear upon all cattle,
On men, all creeping things,
That they may not catch the (grey wolf),
That they may not rend his warm skin!
My word is binding, more binding than sleep,
More binding than the promise of a hero!
Then he springs thrice over the tree and runs [or flies] into the forest, transformed into a (wolf).
Mind you it may not work, but as with all magick intent is the key, if you only do it without the conviction of it working, it won't work. But if your belief is strong enough it'll work. I've ()'d anything that needs to be changed, with the exception of gender specific stuff. The 's are my addition.