This is generally in Mike D.'s wheelhouse, but he basically left the bird site (and I haven't joined any of the new ones), so I haven't seen whether he offered an opinion on the subject.
To me, it is a sufficient parody because it is notably different than the original, and it contains a satirical element. But there's also a dilution element, as both are comic strips. I don't think the parody work is deliberately misleading, but I also wouldn't want a six-digit legal bill just to prove I'm correct.
It is not, however, defamation.