A. In The Family Tree Guide to Finding Your Ellis Island Ancestors (Family Tree Books), author Sharon DeBartolo Carmack says babies born at sea are generally listed on the last page of a ship’s passenger manifest, or at the bottom of any page where the ship’s clerk could find room. When looking at online passenger manifests, you would need to use the controls for the record viewer to page through the list for your ancestor’s ship.
Strange markings in the margins next to a name are a clue to check the last page of a list, or the ship’s Record of Detained Aliens and Record of Aliens Held for Special Inquiry (these are on supplemental pages of the list, following the pages with the passengers’ names). See this Guide to Interpreting Passenger List Annotations for help deciphering unfamiliar notations on passenger lists.
Notations on the passenger list won’t always give you a clear indication that a passenger gave birth on board, though, so if you suspect such an event, scan the entire list for names added during the journey.
Parents could seek birth certificates for newborns once they arrived at their destination. That doesn’t mean they always did, particularly before state-mandated birth recording. For help looking for your ancestors’ birth records—including what to do when you can’t find a record—see the December 2006 Family Tree Magazine.
In modern times, when a birth or death occurs at sea or on an airplane, the birth is reported at the next port of call. Learn more about in-flight births and the baby’s citizenship at people.howstuffworks.com/air-birth.htm.