Is it unethical to track app usage through REST API calls?

Question

I am building an app that communicates with my website with ASIHTTPRequest to a PHP-based REST API on the server side.

Naturally, in my app I have different endpoints on the server side, and usually return JSON data.

Is it unethical to log counters on how many times each endpoint was hit?

I'd like to capture how the app was used capturing what endpoint was hit, the user agent, time of day, possibly their IP (to group visits etc).

Should I ask permission to do this?