They had a son named Joachim Karl Hartert (1893–1916), who was killed as an English soldier during the Battle of the Somme in France.
[3] On 4 May 1892 Claudia Hartert and her husband left Le Havre, France, for an extended trip to the West Indies in the Caribbean Sea.
In The Feathered World (Die Gefiederte Welt) she published many observations and illustrations from her trip to the West Indies.
The couple lived a normal life there despite their dual allegiances to Germany and England until the beginnings of World War I.
[3] In 1939, due to political difficulties, and with the help of British ornithologist Phyllis Barclay-Smith, she moved from Berlin to the St. Willebrordus nursing home in Wassenaar, Netherlands.