When Motley first appeared on the club scene in 1981 this was Nikki's only bass. There are also pictures of him playing it in his previous band, London. There were a few others with them in LA, but they weren't ubiquitous at all. In and around the Los Angeles club scene, Thunderbirds were few in a sea of Ps, Stingrays, and even Yamahas and Peaveys. BC Rich, even with their wild shapes, were boutique bass at the time. I had a '77 Eagle that was more exotic than rock (granted, it was Rich's most tame body style, but almost nobody had any of the others at the time either).
Within a few months of Motley playing out, Thunderbirds started popping up on flyers and on stage among the new crop of "Metal" bands that soon outnumbered the pop and punk bands by far. Their prices started climbing in the local Recycler (free classified ads) and it wasn't long before you saw at least one on every three act bill in Hollywood every single weekend. Nikki's white bird eventually died as a result of his stage antics and he replaced it with a crop of BC Rich basses he got in an endorsement deal in mid-late '82, but he went back to playing birds the second he found someone who would make them for him (Hamer) and has only rarely strayed from them since. He went back to Gibsons in the early 90's (though he may have had them sooner, he endorsed Spectors through '91 or so).
For a couple years there, Thunderbirds were everywhere (check out Headbanger's Ball videos from the late 80's and you'll see a hell of a lot of birds; Hamers, Spectors, BC Rich, ESPs, Jacksons; usually custom shop models made for endorsers because everyone wanted a Thunderbird.
By the time it was a noticeable trend outside of LA, Nikki was already playing the Richs, but Motley's meteoric rise on the LA club circuit definitely got that ball rolling in '81-82. Gibson had to have noticed that.
