I don't think merely being a military type is enough to qualify the aeroplane as a 'warbird'. I don't think of our Chipmunk as such.
To qualify as a warbird, I'd have thought that the type must have seen war service. An L4 Cub qualifies because it was a WW2 spotter and utility aircraft (and it's rumoured one once knocked out a tank using bazookas - but that's the iceing on the cake ;~).
SSD