Lazy cat, active cat

Question
QUESTION: A little over a year ago my mom and I rescued a cat that was between 3-4mos old from a home with a cat that REALLY didn't want him there. He is an exotic short hair and true to his breed, he is a very mellow and laid back cat. The dogs we got (all about the same size as the cat) "play" with him-which usually means they chew and trample on him-and he just lays there. Lately he's becoming less lazy blob and more typical cat.
For example, he always had SOME interest in our birds but was too lazy to even chase after them when they got out of their cage. The other day he actually pounced and held onto a cage. Later the same night he pulled a candy wrapper out of my bedroom garbage container and ran off with the wrapper-twice! He's also taken to chewing on one of the empty and clean bird cages.
I for one don't mind his behavior (other than the garbage thing) and if he goes after my parrot, he'll learn quick how BAD of an idea that is. My question is, what could have caused such a sudden change in such a lazy cat?

ANSWER: Hmm. I'm wondering if something didn't happen to him (playfully) that suddenly got him into this new mode. Is he neutered? Because hormones have a funny way of changing a cat. Is he strictly indoors? Are there new cats outside? You would be surprised at the smallest things that can trigger a cat's behavior. Otherwise, my famous personal quote is, "cats will be cats."

---------- FOLLOW-UP ----------

QUESTION: He has been neutered for a while now and is strictly an indoor cat. The only thing that changed was that we bought him another scratch post

Answer
Does there happen to be catnip intigrated in this new scratch post? But I think it's safe to say that unless you can think of anything, even completely random, that you can just accept his new behavior and use deterents for those things you do not want him doing.

Let me know if there is anything else you can think of.