"What we've most noticed about New Zealand is the diversity of geology and wildlife due to its isolation and longitude," he said.
"New Zealand had some of the most remarkable birds that ever existed."
After months of scouting, the BBC chose the weka living at the Orongo Bay campground where a re-vegetation and predator control programme has restored the habitat; the Chatham Islands' black robin which also showcases a unique landscape and successful repopulation project; and the flighty little fantails which were constant companions during the filming of geothermal Rotorua.
"The fantails were ridiculously fast and had no consistency to their flight," Mr Walker said.
"Weka are probably the boldest birds we've come across. They are curious and check out everything slightly edible."
The film-makers have been battling unreliable spring weather. They film mostly early or late in the day and rest in between when the light is harshest and the birds are also less active.
Weka were reintroduced to the Bay of Islands in the 1990s. The birds, of the rail family, are now thriving. When it comes to venturing into spaces shared by humans, weka are strongly motivated by greed, and are possibly far more popular with the BBC than with local gardeners.