Man’s worst friend

In a coun­try where our most pre­cious birds can’t get off the ground, it’s no won­der that we have be­come the rat’s worst en­emy.

Element - - Well Being - PAUL THOMP­SON

Ac­cord­ing to con­ser­va­tion bi­ol­o­gist James Rus­sell of Auck­land Univer­sity New Zealan­ders have been locked into a “co-evo­lu­tion­ary arms race” with rats since they first hitched a ride on Euro­pean ships of the 18th and 19th cen­turies. “Hu­mans are very good at sur­vival and rats are one of a num­ber of species that are good at sur­viv­ing with us. Wher­ever we go, rats are soon to fol­low. As we de­velop new ways of be­ing able to con­trol rats they will evolve a way to avoid be­ing con­trolled whether it be by be­hav­ior or ge­netic adap­tion.” It’s a strug­gle that has seen New Zealand be­come fully in­fested with, in par­tic­u­lar, Rat­tus rat­tus or ‘Ship rat’ which ac­cord­ing to Rus­sell has now reached ev­ery area of avail­able habi­tat in main­land New Zealand and lives in high den­si­ties ex­cept on those re­serves and off­shore is­lands where rats have been

33% of all global rat erad­i­ca­tion pro­grams have been run by us.

erad­i­cated and ex­cluded.

While rats may have pretty much over-run us we have re­sponded by be­com­ing world lead­ers in their man­age­ment and erad­i­ca­tion. ‘We are the best in the world. Pest con­trol and other con­ser­va­tion tech­niques are the ‘sil­i­con val­ley’ of our tech­no­log­i­cal ex­port,” says Rus­sell – which sort of makes him the Steve Jobs of global rat con­trol – with calls far and wide to ad­vise and as­sist, in­clud­ing at an eco ho­tel on Mar­lon Brando’s pri­vate atoll in French Poly­ne­sia. Cur­rently 33% of all global rat erad­i­ca­tion pro­grams have been run by Ki­wis. In the 1990s it was more like 50% but as we ex­port our knowl­edge so other coun­tries be­come skilled at deal­ing with their own prob­lems.

The pace at which rats can pro-cre­ate and cause dev­as­ta­tion to na­tive birds, in­sects and plants is as­tound­ing. In 1963 a cou­ple of rats got out to Big South Cape Is­land – a mut­ton bird­ing is­land of about 2000 hectares, just south­west of Ste­wart Is­land. Within one year rats were across the en­tire is­land but at a low den­sity. Three years af­ter first ar­riv­ing they were across the en­tire is­land at high den­sity, two species of bird and one species of bat were ex­tinct and a num­ber of other plants and in­ver­te­brates were also lo­cally ex­tinct.

We are talk­ing here in par­tic­u­lar about the Ship rat, the most dam­ag­ing, per­va­sive and preva­lent of the three species that in­habit New Zealand. The oth­ers are the Nor­way rat and the small re­main­ing pop­u­la­tions of Kiore or Pa­cific rat which, though con­sid­ered a pest by DOC due to ev­i­dence of pre­da­tion on na­tive birds, lizards, plants and in­sects, have cul­tural sig­nif­i­cance for Maori, es­pe­cially Ngati Wai, who see them­selves as their guardians. What makes ship rats such a threat to New Zealand’s flora and fauna is their adapt­abil­ity – or ‘plas­tic­ity’ as Rus­sell calls it. “They are able to sur­vive in the most ex­treme en­vi­ron­ments, on is­lands from the high­est lat­i­tudes through to the trop­ics.” Rats are om­niv­o­rous and their diet mostly con­sists of 50% plants (fruit, seeds and seedlings) and 50% in­ver­te­brates. Birds, its sur­pris­ing to find, are not of­ten on the menu be­cause of their com­par­a­tive rare­ity. “Even though they have such a neg­a­tive ef­fect on our birds and lizards its very hard to find a rat that has eaten a bird or a lizard be­cause it’s a very rare item for them – a bit like caviar to us. How­ever, there are so few birds and so many rats that only a few of the rats need to take birds for this to have an im­pact.” The im­pact is still huge, ac­cord­ing to fig­ures from Land­care Re­search; in 2012 rats, stoats and pos­sums ac­counted for some 26.5 mil­lion na­tive bird deaths in New Zealand’s forests.

The ship rat has de­vel­oped a habit here in New Zealand that is unique in all the world. Be­cause there are no other mam­mals that might prey on or com­pete with them in our na­tive forests this is where they have es­tab­lished their high­est pop­u­la­tion den­si­ties with much lower con­cen­tra­tions in ur­ban ar­eas. The prob­lem is ap­par­ently as bad as it can get and now it’s about “re­claim­ing the ter­ri­tory” ac­cord­ing to Rus­sell. Money has key part to play, DOC cur­rently has fund­ing that en­ables it to carry out pest man­age­ment on a mere four per cent of New Zealand’s land mass. Whilst there have been ma­jor suc­cesses on off­shore is­lands there is still a huge amount to do. As work turns to­wards pop­u­lated is­lands such as Great Bar­rier Is­land

there are chal­lenges other than fund­ing that make things tricky. Its not that peo­ple are op­posed to rat erad­i­ca­tion but there are is­sues over the meth­ods pro­posed. While traps are widely con­sid­ered to be hu­mane in that the kill is usu­ally in­stant but there are grow­ing ques­tions over the hu­mane­ness of anti-co­ag­u­lant tox­ins.

Many might think that the way in which we kill our pests is ir­rel­e­vant to the task of con­trol­ling them. But for Stu Barr of Welling­ton based Good Na­ture it is an is­sue for us all. ‘‘We are world lead­ers and we should be seen to be man­ag­ing pest species in a hu­mane man­ner. It is im­por­tant how we as hu­mans treat the or­gan­isms within our en­vi­ron­ment.” Good Na­ture has de­vel­oped a range of hu­mane self­set­ting traps that are cur­rently be­ing tri­alled by DOC in six large-scale sites around the coun­try. “It doesn’t help us to sim­ply de­monise rats, they are do­ing what they do nat­u­rally and cir­cum­stances have brought them along­side us and this en­vi­ron­ment. It’s our de­ci­sion that they should be con­trolled to pro­tect other species. We aim for no suf­fer­ing. Us­ing those tox­ins you know there is a pe­riod of suf­fer­ing be­tween in­gest­ing tox­ins and their death.”

A hu­mane method of de­ter­ring rats from com­ing into your home can be found with the plug-in de­vices which they find un­pleas­ant. A com­puter-gen­er­ated sig­nal is sent through the elec­tric ca­bles at vary­ing in­ter­vals in the build­ing caus­ing the elec­tro­mag­netic field to pulsate. The ben­e­fits of this is that also de­ters cochroaches.

In the end we must re­claim our unique en­vi­ron­ment while we still can and it would be pru­dent for this to be re­alised for what it is worth to us all. Just be­cause many of us can’t see the rats in the trees af­ter dark as they rob nests of mil­lions of na­tive birds doesn’t mean we should turn a blind eye. Con­trol­ling rats on our land and in our gar­dens has sig­nif­i­cance as so many of our in­hab­ited ar­eas are close to pris­tine na­tive land­scapes. Rus­sell points out that we have an eco­nomic im­per­a­tive to con­tinue the work we do so well over­seas here in New Zealand. “There are a lot of is­lands in the world in the mid­dle of nowhere and we just hap­pen to be one that has an amaz­ing con­ser­va­tion rep­u­ta­tion which sees tourists make 12 and 24 hour flights to come here. If we didn’t have that one edge then peo­ple would go to some

other is­land closer to home.”

Photo: David Mudge

Our na­tive birds have lit­tle or no pro­tec­tion against rats.

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