Assorted Topic #2 - Infestations

When humans first arrived in New Zealand around 1300 AD, the islands had existed in almost total isolation for millions of years.  There were no land mammals, but endless flavors of birds.  Without the threat of predation from the ground, many birds (including the famed kiwi) evolved to be flightless, and filled niches typically taken by mammals.  Moreover, many evolved to be huge.  For example, the moa (think of them as the cows of the bird world) were flightless and stood up to 12' tall, and the Haast's eagle (which preyed upon the moas) had a wingspan of up to 10'.  It was a garden of eden for birds.  The early European visitors described the noise level from all the birds as approaching deafening.

Unfortunately, the current birdlife is a mere pittance of it's past glory, with many species either threatened or extinct.  When the first humans (Maori) arrived from Polynesia by boat (cira 1300 AD), they introduced rats, which had a heyday with all the bird eggs.  The Maori hunted to the moas to extinction, and the Haast's eagles followed shortly thereafter. 

The Europeans, who began arriving in the late 1700s, made a series of unfortunate decisions that made matters worse.  In the mid 1830's, they imported Brushtail Possums from Australia primarily for their fur pelts, but also as a source of food.  They loved the bird eggs!  The Europeans also introduced rabbits for hunting in the mid 1800s, which thrived on the pasture grass, and quickly became a problem for farmers, who wanted something done about it.  So, ignoring warnings of scientists about major harm to bird populations, the powers that be introduced weasels, ferrets, and stoats to reign in the rabbits.  Well, the bird eggs were much easier hunting than the rabbits, so the scientists proved to be correct.

Stoat (photo courtesy of dkfindout.com)

The stoats, possums, and rats are all considered to be significant threats to the birdlife ... and programs are ongoing to reduce the populations.  We saw probably hundreds of traps for stoats (a particularly veracious eater of eggs, and chicks), as well as signs warning of spraying for rats.  Apparently, the efforts are helping, as birdlife is returning in areas with these control efforts.

The possums, with no significant predators, (surprisingly?) blossomed into an infestation over the next 180 years, and cause all sorts of grief.  They love to eat many parts of trees and bushes, dramatically stunting their growth.  They put pressure on the bird populations by eating their eggs, reducing their food supply (foliage and berries), and reducing their nesting habitat (e.g., tree hollows).  They are particularly effective carriers and transmitters of bovine tuberculosis, causing significant problems for both cows and deer livestock.  Plus, they run under moving car tires, leaving a big mess on the roads!  We had heard they were considered a nuisance, but hadn't seen any as road-kill for quite a while on our trip ... only brown furry things.  Well, we finally figured out that possums in New Zealand are not the same as in America (where they are technically opossums) ... but are, in fact, brown and furry.  The Australian version was named a possum by an early explorer since it looked like the American opossum.  I don't see the similarity myself, but you be the judge.  In my opinion, one looks like a scraggly prehistoric rat, while the other looks like a cuddly pet.

Opossum (photo courtesy of Wildlife Rescue and Rehabilitation)

Brushtail Possum (photo courtesy of teara.govt.nz)

Other than road-kill, the only possum we saw was on a trail-side tree with its head stuck in a blue wedge.  We were freaked out for a bit, but the absence of motion suggested it was dead.  Later research provided the details of the trap, which looked like a giant mouse trap.  Not sure if it was part of the national eradication effort, or just a hunter.

Ouch!

Similarly, numerous types of pine, fir, and larch trees were introduced for forestry and to prevent erosion.  Over time, these species have started crowding out native habitat, including the tussock grasses in the alpine areas of the mountains.  Efforts are ongoing to eradicate these "wilding pines".  Near Queenstown, we took a gondola up a mountainside, and were struck by how similar it looked to ski lifts in Washington.  Probably because all the trees were Douglas Firs.  Higher up on the hillside, there was a clear line above which all the trees were dead.   On the Queen Charlotte Track, we also saw a number of areas where the pines were dead.

Dead pine trees on the far hillside from the Queen Charlotte Track

Signage on Queen Charlotte Track

More recently (the mid-20th century), several types of foreign wasps have been introduced, and are now considered invasive.  The main threat they pose is that they eat the sweet honeydew produced by scale insects that live in the bark of beech trees, depriving birds and other insects of a key source of food.  These wasps have really got it figured out, too.  They increase the amount of honeydew produced by the scale insects by eating it directly from the source as it's produced, eventually killing the scale insect.  They eat something like 90% of the honeydew.  Needless to say, there are eradication efforts ongoing.

Wasps on black beech tree.