If you have a blog and start to use FeedBurner to manage your feed, you have to change the autodiscovery link in your template and redirect the old feed to FeedBurner, so you don't have to tell your readers to subscribe to the new feed. Until today, there wasn't option to redirect the feed in Blogger, but now you can simply go to Settings > Site Feed > Post Feed Redirect URL and add the address of your FeedBurner feed.
... but Blogger only remembered about the first one. The other three don't redirect to the new feed, which is pretty strange, considering that the feed #3 is new Blogger's default feed.
FeedBurner's blog notes that "by redirecting your feed, you can get a true picture of how many subscribers you have. Some of you might even see a few more subscribers magically appear, though results will most certainly vary."