I've slowly begun reversing this with my male ekkie. Ekkies are notorious for this talking: it's often referred to as closet talking, talking when no ones around as a means to get you to come back. It's an attention getting device.
Bringing it out of the closet is doable, just requires extreme consistency on your part. after about a year we hear a LOT more chatter when we are near him and within eyeshot.
Here is how you do it:
Prep:
1) Charge your keyword-. You know how you say "yay!" Or "good boy!" Whenever you pet does something good? You need to charge it so it means something. "Good" becomes a bridge to good treats.
Research how to start clicker training: you'll charge the clicker to teach the animal that *click* means a treat is coming. The way this is done is to click the clicker and IMMEDIATELY give a treat. *click*-treat, *click*-treat.
Charging your word, "good" for example, gives power to this word like charging the clicker gives the clicker power So you say "good", and immediately treat. "good"-treat, "good"-treat. YOU ARE SUBSTITUTING THE WORD FOR THE CLICKER.
The treat must be his most favorite food in the world that you are aware of, and he can only get it when charging the word and as a treat for speaking. For Parker, I used bits of shredded cheese as an initial exciter (it's not healthy so I use it initially to accelerate any training and then back off quickly), and then substitute popcorn later.
Be sure to use a consistent tone/pitch each time. Dont vascillate between a high drawn out, and low/short "good".
This takes 2 days. 3 sessions per day, 15-20 treats per session. You can use a clicker, but the point here is to click when he speaks, and treat him. You may not have a clicker handy when he does, so your voice is better since it's always handy. during this initial charging process, don't reward talking because he has not had any association with the treats and talking yet.
2) identify situations where he's most likely to talk or whistle (yes, include desirable sounds, including whistles if you want them). For Parker that is when he is left alone and when he's around running water. Put him on a shower curtain while you shower or on a stand while doing dishes and he ant shut up!
TIE IT ALL TOGETHER: simple. With your newly charged keyword, anytime he talks, you shout the keyword and come running with a treat. Here's the consistency part: he needs to now that word equals treat. You must shut the keyword and provide a treat every time. I can't be too much lag time between the word and the treat, so I strongly recommend you keep treats at various locations in your house so you always have them handy.
Prep number two above is a way of accelerating the process. This is how I sped up Parker's process because I already knew that he goes crazy when I bring him into the bathroom with me when I shower.
you should be able to see some sort of change relatively soon. With Parker, after about three weeks he randomly said "hi Parker" while sitting on my hand as I was walking him to his cage for bed. Of course he got an immediate treat, since I had them near his cage as well. He went on for another week saying something maybe every other day as I was putting him to bed. I often now get a "hi Parker doodles" as I'm putting him to bed. I've even gotten a "good night Parker" once or twice.
I hope this makes sense, and I wish you good luck! Let me know if you have any questions about the above.
