This species was thought to be extinct for fifty years until it was rediscovered in 1948. Small numbers of birds were translocated to several predator-free offshore islands, including Tiritiri Matangi. All of the individual birds there are banded and carefully monitored, but they are free-living. They have done well enough in these offshore sanctuaries that they are starting to release them back on the mainland.
The second bumble nest down the Burrows track is still very active, but I've only seen one bee larger than the very small workers, enter.