Birds are free to fly wherever they want with no boundaries. Many cultures believe that birds are a symbol of eternal life; the link between heaven and earth. Life and death.
Crows especially are mythical birds. Besides from being the link between life and death some says that crows are signs of change. That all that you have been working for and toward is now coming to fruition. Some say that crows will give you clear messages and guidance (in dreams) as to what your next steps are.