We reported on a 'Birthdays' widget back in mid-December (here), only then for it to disappear out of the blue. As of yesterday, the widget appears to be back in the form of 'Upcoming Birthdays' and should now be visible to you in the stream (if you have people in your circles with upcoming Birthdays of course).
Birthday reminders has appeared in several places, including the Google homepage and more recently in the form of Google Now cards, which are here to stay. So having them back in our Google+ streams seems like the obvious thing to do.
The widget will appear several days before the actual date of the Birthday of the person in your circles, giving you plenty of time to send out a card to them (if you actually know them, of course). On the day, Google+ will prompt you to "Make a wish", clicking on the button which will appear next to the person's birthday on the widget will bring up a box for you to send a personal message.
We were at first hesitant to post about this, but it seems a lot of users have noted the sudden reappearance. We did reach out to Google for confirmation but have so far, not gotten a response. In the meantime, we'll be treating this as an update.
Are you seeing the Upcoming Birthdays widget?