In the postcards, there's quite a big difference between flight = diving. While the flight fantasies all involve mechanics (proven to work at least in 1910), mo

In the postcards, there's quite a big difference between flight = diving. While the flight fantasies all involve mechanics (proven to work at least in 1910), most diving fantasies involve training sea animals in some way. So why didn't they think of using birds for flight, or the other way round, mechanics to dive? My guess is "racing fish, whale bus etc." was intended as a joke.