In checking out the 1920 and 1930 U.S. Censuses, I found Gustav's brother Alois--who had changed his name to Hans Christian Mahler--in Chicago, listed as a real estate salesman. In 1930 he was 62 years old, and I believe he died later in the 1930s.
In searching the New York Port of Entry passenger lists, I found both Gustav and Alma arriving on Nov. 21, 1908, and Oct. 25, 1910. On the 1908 list, his occupation is given as "band master." Some band. Some master. That sailing was on the S. S. Amerika out of Cuxhaven, a nine-day voyage.
The 1910 trip was on the S. S. Kaiser Wilhelm II out of Bremen, a seven-day voyage. On this list he is put down as "director of a band," a little better perhaps. The passage was paid by the Metropolitan Opera Company, according to the entry.
Here's an interesting item: Gustav was 5' 3", and Alma was 5' 8". (I think Alfred Roller estimated Mahler's height at about 5' 4".)
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