I did wonder if it had to do with nesting but had dismissed that thought since he's male and neutered (and single). Rabbits never cease to surprise.
I should have clarified, Jenny. By stating he wasn't eating it, I was referring to just the mouthful of hay he was holding. He had eaten a big pile of basil right before this. He's eating fine.
Within the hour (& after I posted), he was lounging in his litter box without the hay in his mouth. In the 5 years of having him, I've not seen him do that nesting thing. Silly bunny.
Perhaps one of you would have some further insight as well. Now I'm wondering if this behavior is somehow linked to another recent change in his behavior. He had lost his bondmate 2 years ago. After that, he came out of his shell and became bolder and more interactive with us (and the dogs). He had his nightly routine of coming out to the couch and begging for treats (something he barely did when he had Sapphire). He even binkied more and seemed more adventurous. (this was a big reason why we didn't seek out a new bondmate for him)
Then, these last few months, he won't come out of his cage. The door is left open from morning til midnight -- just as it always had been even before his bondmate passed. Even shaking the jar of banana chips, while it gets his attention, won't coax him out. This behavior has bewildered me. However, when he is in his cage (door open) he seems very much relaxed. And in the morning, he tosses his ball around if I don't get the cage door open quick enough. He wants it open, just won't come out.
For all the time we've had him, the cage door has always been open all day, every day. He's always gone out every day. There is nothing that has changed (that I can think of -- and believe me, I have tried to think of anything to explain this). Just these past months, he refuses to come out. Could this have anything to do with the 'nesting' behavior?