Well, that was an interesting read! Indeed Denis knew very little, when he started out, and was very lucky not to have been killed a few times. But hardly anyone knew much anyway. Denis had a big advantage in that he was a bit of an inventor on the side; one of his inventions was still (in 1963) the standard method used in the film industry to equalise film colouring if it was a bit variable. That background enabled him to lash up all sorts of gear to film animals in difficult situations. And, though he had a romantic view of the ecology, he did change the world (not enough yet).
I think the guy is a hero.
Now beginning to read my way (for the second and, in some cases, the third time) through Katharine Kerr's fantasies.
MG