How can I allow managers to view their subordinates' birthdays on the Leave Calendar?

This feature is available on Premier and Master editions
In order for managers to view their subordinates' birthdays, permission to the About Widget Birth Date has to be granted under the "Employee" menu branch on the Manager Self Service Security Role.
Navigate > Config > Security > Security > Security Roles
Step 1: Click on the pencil icon to edit the Manager Self Service Security Role.
Step 2: Click on the Permissions tab and expand the Employee Public Profile parent permission.
Step 3: Grant access to the About Widget Birth Date permission.