Science Heresy - October 2012
Antarctic Tern at Macquarie Island
Refutation of John Reid's Article
It is the first time I have seen someone criticise the Macquarie Island pest eradication project based on sentiment - because they liked the island better with its feral fauna! Other previous criticisms have mainly been based on regrettable by-kill of native birds, or supposedly better uses of the money.
Actually I sympathise with John in a general way - though not in this specific case. Conservationists can get quite extreme and indulge in futile attempts to restore ecosystems (in continental regions) to their 'natural' state, whatever that may be. Such efforts are often useless and in the process destroy features of one kind or another that might be regarded as desirable to many other people - exotic trees and animals, access, etc. But islands are special, and different, in two main ways: firstly they are isolated, and their biotas have evolved in isolation and are therefore especially vulnerable and unable to adapt to introduced species; and second, it is possible to do something about it in such small isolated places and subsequently keep them that way. Macquarie is a good case in point.
The eradication project there has been an outstanding success, watched with interest by conservationists, scientists and park managers all over the world. Undertaken by Kiwis - the pioneers and experts in this area - it has been the largest island so far treated in this way, and the only one in which three pest species (rats, mice and rabbits) have been simultaneously dealt with. It has been an extraordinary success (with some mistakes from which lessons have been learned). Rats and rabbits (the most damaging two of the three) are almost certainly extinct, and mice may well be also. The response of the vegetation has been amazing - I'd love to go back to see, but the photographs are themselves impressive. Birds are visibly benefitting too (although to the larger penguins, like the seals, it's all irrelevant!). Antarctic Terns are now nesting on the ground in shingly areas behind beaches where they have not nested in living memory, due to rat predation. Likewise blue petrels are now nesting on the main island and not just on offshore stacks. Presumably they have been trying to do so for decades and failing due to alien predators - only now can they succeed.
My two years on the island postdated John's. I missed the wekas, and I have read with interest some of the interactions between them and people. One person wrote in a hut logbook about a weka he had tamed to jump up and take tinned sausaged from his fingers - a game that brought painful trouble one day when he was standing outside the hut relieving himself! But I do have personal experience of a near-relative of the weka (banded rail) pecking bird nestlings to death on another island; they are opportunistic scavenger/predators and undoubtedly had a deleterious effect on ground-nesting birds (although it turned out in the end there weren't that many of them as thought which is why they proved relatively easy to eradicate). I did see many cats, dead and alive, various colours and feeding on more than just rabbits. Since they were eliminated in about 1999 (except for one individual they could never get, which must be now long-dead of old age) grey petrels have returned to breed in increasing numbers, though unrecorded nesting previously (since 1948); again this (winter-breeding) burrow-nesting bird must have been 'trying' to breed year after year, and failing through predation. There used to be a house cat at the station called Rover, who finally died a year before I first went to the island - tolerated, even loved, for its company and for its rodent controlling abilities - with the rockhopper penguin chicks it brought in from nearby Garden Cove being conveniently overlooked.
The rabbits reached plague numbers in the 90's for a combination of reasons. They had previously been at similar numbers in the '60s but were knocked down by myxomatosis. The myxomatosis virus ceased to be available (nobody was manufacturing it) in the late 90s, so that control was lifted. There were also a few unusually mild, dry winters in the noughties which permitted better breeding and survival by rabbits during the harshest season (more of that below). And the third reason of course, the one John latches on to, is the removal of cats. Incidentally, it is of interest that cats were present on the island long before rabbits, but only after the latter were introduced late in the 19th century did this extra food supply permit the cat population to increase sufficiently to eliminate the parakeets (whose reintroduction from the Auckland Islands is to be looked forward to now the cats have gone). The rabbit damage to vegetation was cumulative over decades; the huge population in the noughties, though not unprecedented, added its impact to earlier ones and the results were horrible - large areas of dead tussock, other plants nibbled flat and in at least one place (near Bauer Bay) whole slopes totally denuded of vegetation - and eroding rapidly as John pointed out.
By 2010 the rats also were more abundant that ever. I remember leaning on a tussock - which squeaked! Their holes were all over the place, and even by day it was common to spot a rat disappearing into its lair. There were few on the highest parts of the island (although mice were there), but in the areas of grassland in which the smaller burrow-nesting seabirds like prions were most likely to be seen there were lots of them - eating eggs and nestlings in no doubt large numbers. In the evening it was a joy to see these smaller birds winging their way in towards their nests from the sea in their dozens - but at islands without rats, like Heard, they do so in their majestic tens of thousands.
An unexpected but very conspicuous consequence of the pest eradication was the return of the native invertebrate fauna. For example, after dewy nights I am told that whole hillsides now sparkle with dew drops on the ubiquitous spider webs; nobody alive had ever seen this before. The rodents (perhaps mostly mice in this case) had been eating almost all of the spiders and insects.
The Azorella dieback has been portrayed as a 'mystery', as quoted by John, but no pathogen can be found. Almost certainly (as shown by on-going physiological investigations as well as meteorological data) it is due to drought, strange though that might appear to human eyes in such a place. It turns out that these plants, evolved as they are in an environment of nearly constant mist and rain, are very poor at moving water through their tissues, and too many sunny days simply dry them out. I hear there is some good recovery going on in the last couple of years with more 'normal' weather - whether this dieback turns out to be some sort of normal but infrequent event, or whether it is a reflection of a changing climate remains to be seen. The dieback was at its worst before the eradication project began, and has since ameliorated, so that no interaction can reasonably be suggested.
Macca is a wonderful island - like John I have the fondest memories of my time there. No doubt it will always be so, and the larger fauna would have remained almost completely unaffected by feral animals whether present or absent, or indeed by the sorts of human activities that have been going on there over the past sixty years or so. But it is my strong view that it will hereafter be an even better place as a result of the success of the pest eradication program - the plants, smaller birds and even the invertebrates are also a part of the place, and deserve to be there, while the rodents, cats and, yes, the wekas too, really have no place there and are better gone.