The Birthday calendar is not an actual calendar that we can access but is rather composed on the fly based on contact information (that Morgen does not read at the moment).

The current workaround is to export the Birthday calendar into an .ics file using the Export function on Apple Calendar, drag the file on the Morgen calendar view and import the events into another calendar.

I will leave this Feature request open for future consideration.

YES! Me too! Ive already missed several birthdays because of this and that is upsetting.