Fernbird, those endearing fearless inhabitants of lowland swamps, gumlands, salt marsh and pakihi are colonising a National Park subalpine zone. Almost certainly this is thanks to DOC West Coast maintaining a continuous 50 year 1080 pest control programme in the Otira Valley of Arthur's Pass National Park.
Ask around New Zealand and everyone who knows fernbird will tell you about their encounters with them in pakihi (West Coast), saltmarsh (Pollen Island Auckland), gumlands (Northland) and swampland (Te Anau Basin). They won't describe them as a bird you find in subalpine shrubland and alpine herbfields living alongside Kea parrots and Giant Buttercups (Ranunculus lyallii).
And yet that is exactly the new habitat that fernbirds are colonising in the Upper Otira Valley and on the summit of Arthur's Pass in the middle of Arthur's Pass National Park.
Read some of the old naturalist writings of the High Country in the 1800s (eg TH Potts "Out in the Open") and you will see that fernbird were once considered a sub-alpine bird. Then stoats were introduced, possums became much more widespread and, to the best of my knowledge, fernbirds became extinct in these places.
Perhaps they survived stoat predation in the lowland swamps, gumlands, pakihi and wiwi simply because these are such tangled, impoverished, wet and generally hostile places for predators to invade. Meanwhile stoats had easy access into subalpine tussocklands and shrublands and wiped out the resident fernbirds and takahe, kakapo and lots of other birds.
Yesterday, 14 December, with a group of keen birdwatchers on the summit of Arthur's Pass, we heard the "U-Tick" of a fernbird, squeaked it up and sure enough it came and jumped all around the plants beside us. Last summer, January and February 2010, we watched exactly the same behaviour by fernbirds in the subalpne grasslands of the nearby Upper Otira Valley. We then thought that to be unusual and reported it to DOC's fernbird experts who were equally puzzled. This second season of fernbird sightings suggests that fernbirds are now permanently resident in this new habitat.
The only significant difference between the Upper Otira valley and any number of other subalpine sites along the Southern Alps, is that this valley has been subject to over 50 years of continuous 1080 pest control by the Forest service, Animal Health Board and DOC.
Fernbird are the second native bird species to spread south into this subalpine National Park environment in recent years. Western Weka have spread south right across Arthur's Pass summit and down the Bealey Valley into Arthur's Pass Village where they are now resident. Robin have also returned to Arthur's Pass Village where there has been a 10 year long community pest control programme.