Is the "dolphin call" from the TV show Flipper and The Bourne Identity (2002) actually a modified kookaburra call?

A comment below Who pioneered the use of Laughing Kookaburra birds to create the impression of a jungle setting? links to a The Sound and the Foley blogpost That Jungle Sound which explores the use of this bird’s "laugh" to create an impression of being in a jungle setting.

At the bottom of this post are lists of movies and television shows in which recordings of Kookaburra are employed. One of them caught my eye:

In Flipper (the 1964 TV series), the titular dolphin’s famous cry is actually a modified kookaburra call. (!) (This “dolphin call” can also be heard at the very end of The Bourne Identity (2002).)

I recall sitting in the theatre at the end of The Bourne Identity and immediately thinking "Flipper!" But what I find surprising here is the claim that "This ‘dolphin call’ is "actually a modified kookaburra call."

Question: Is this true? Is there any information to support this? It’s hard to imagine there was technology available to do such a thing in the 1960’s, nor a need to.