UPDATE! So, after worrying for days and supplementing him with Nutri-Drench I finally, after all these weeks, have concluded that Clark must have been utterly humiliated by one of the older girls. Seriously, he's fine! He gave up crowing for sex!!! He's interested in mounting every girl in the yard and the ducks who have become savvy in terms of getting away from him or jumping in one of their pools. I have no idea what the heck happened - maybe someone pounced on him or who the heck knows...what I can say for certain is he's eating well, acting normally, bright and active and interesting in mating all the time. As for crowing, hardly a crow out of him. He keeps alert to predators and is clucking his treats for the girls song but crowing just isn't his thing.
Works for me and definitely for the neighbors who asked whether I got "rid" of the rooster. NO I did not and don't plan to either.
Happy ending to a weird and worrisome period.