We use Fabric to collect crash reports of the app. This includes information like your phone type and iOS version. There is a unique id on those crash reports, but we cannot tie that unique id to any particular person.
We request access to your list of contacts the first time we launch, so that we can automatically build the list of birthdays and show them in an upcoming order. We do not do anything more with your contact data besides build the list of birthdays. Every time the app re-launches we re-scan your contact list and show the very latest set of birthdays.
We do no other tracking of you as a user or your data.