That's what I was thinking as well. It looks a lot like an egg. Nest-like spaces, egg-like shapes etc can trigger amplified hormonal responses and nesting behavior that wouldn't occur to the same extent in the absence of triggers. That pile of shreddings on the ground could also trigger nesting behavior (especially in conjunction with the ball). You want to do your best to avoid providing them with anything nest-like (no piles of paper, huts/tents, under furniture, bedding/blankets, shadowy laps etc).
They are instinctively programmed to do certain behaviors, but they will do them much less in environment in which they are not triggered by access to certain objects/spaces etc. Exposure to triggers can change their hormone levels and put them into nesting mode etc (which can make them more anxious, vocal, neurotic etc--- just depends). If you are certain he is a male, I would wait until he isn't looking and remove the ball.
I am not sure what I would suggest that you do at this point, but in the future, avoid this.
If your bird is female, there is some risk that removing this object could actually cause her to lay eggs **if she thinks of this as her egg**....If a bird produces an infertile egg, the advice is to leave it until he/she loses interest. I am inclined to say remove it, but the other part of me wonders if you should remove all other nesting triggers (like the shreds etc) and wait until interest is lost...Sorry I can't help more. Definitely not something you want to encourage in the future though.
