Some problems with this question: The Birdy comes with a choice of different handleposts, which will likely have different max heights. I'll assume the Sport 21, which I have and it actually seems to be the only one on offer right now at R&M (don't know about Pacific). Second, since it's a suspended bike, the height from the ground will vary with the weight you put on it, and what elastomers you choose. Even with tyre size and pressure. From the ergonomics point of view I think the vertical distance between bottom bracket and bars might be more useful, but that's harder to measure. Anyway, I'll assume unloaded height. (Reminds me of "The Airspeed Velocity of an Unladen Swallow" ("What do you mean, an African or European Swallow?"))

So on my Mark 3 R&M Birdy (unloaded), with Sport 21 handlepost at max extension, and Schwalbe Marathon (not Plus) 44-355 tyres at whatever pressure they're currently at, the distance from the ground to the center of the bars is ca. 103,5 cm.

Of course you could replace the standard flat bars with riser bars and get considerably higher. The diameter is the common 31,8 mm.
I hope it's useful.