Changing subfield/PhD topic

[tuliula]

Hi all,
I've been admitted for the 2021 Fall to a school that I'm very happy with, at a department of anthropology. Originally when I applied to schools, I had two proposals that I sent to different anthro departments - one leaning towards queer anthropology, the other to animal studies (although there are some connections between the two proposals).

The queer anthro proposal I admitted was the one which got me into my school. There is a specific faculty member who engages with these kind of topics, who also ensured my funding. We corresponded and talked for a few times and we have a good intial connection.

Ideally, I want my Phd project to be the one from the other proposal, in animal studies. It's something well within the scope of the department, and it might be even something that will interest my potential advisor, although its not his main area of interest. I was wondering how to approach and tell him about it, considering its not a minor change of ideas within the same field but rather quite a different proposal - should I discuss it with the departmental graduate advisor first? Should I wait until I arrive there in the fall, or rather try to talk about it in advance in the next few months?

I'd love some insight from anthro / social sciences folks, especially people who've been in this kind of a situation.

Thanks!