Thunderbird symbolically is a protective spirit.
Thunderbird brings the storms, which help the people and animals prosper.

Its feared because of old legends of a giant bird that would snatch people as food until a hero shot an arrow that brought it down.

Its linked to the elementals, my suggestion would be to google thunderbird and read the different stories that pertain to it to find the message for you. It seems confusing because there is no 'bible' per say for native spirituality, its in the stories that are spoken and handed down.

I believe it is good because its the beginning of learning another path. Happy hunting!