It’s not only birds that are contributing to the Aussification of northern New Zealand. Australian plague skinks are now dominating the local lizard fauna.
New Zealand lizards
New Zealand has an astonishingly diverse native lizard fauna, with 104 species currently recognised. But most New Zealanders rarely if ever see a native lizard. While they can be hugely abundant on predator-free offshore islands, at most mainland sites they are both scarce and secretive. Unless you know where to look, and what to look for (or own a cat!), they are easily missed.
What’s in a name?
Despite nearly 100 species of foreign lizards being intercepted at the border, so far only one species has breached the defences and become established in New Zealand.
Known in Australia as the delicate skink, grass skink, penny skink, dark-flecked garden sun skink, or garden skink, until recently Lampropholis delicata was most commonly referred to in New Zealand as the rainbow skink. This name is both confusing and misleading. It is confusing because the name ‘rainbow skink’ is also used for a distantly related African lizard, and misleading because the Australian species is not particularly colourful. It is predominantly coppery-brown, but does reflect an iridescent rainbow sheen when in bright light.
In recent years, L. delicata has become known as the plague skink in both New Zealand and Hawaii, reflecting both its invasiveness and the high densities that it can reach. But there is more to the new name than clarifying ambiguity – there is psychology also. Would you be more concerned about a colony of plague skinks or a colony of delicate skinks being detected on a conservation island?
Plague skinks are native to eastern Australia, and were first noticed in New Zealand at the Otahuhu rail yards (South Auckland) in the mid-1960s. Both the skinks and their eggs can be difficult to detect, and it is likely that they were accidently imported in a shipment of hardwood sleepers.
From there, the skinks spread to Hamilton and Tauranga by 1978, Paeroa by 1984, south-western North Island (Whanganui 1996, Palmerston North 2009, Hawera 2014, New Plymouth 2016), eastern Bay of Plenty (Whakatane 2003, Edgecumbe 2007), Northland and the Far North (Whangarei 2002, Dargaville and Kaitaia 2007) as well as Rangitoto (1981), Motutapu, Waiheke, Great Barrier (2013), Kawau and Rotoroa Islands in the Hauraki Gulf.
Their spread is considered to be human-assisted ‘jump dispersal’, followed by radiation from each new centre.
Absolutely protected to unwanted organism
New Zealand lizards first received legal protection in 1981, and plague skinks (perhaps inadvertently) became a protected species in New Zealand as a result. The Wildlife Order 1981 provided protection for ‘all lizard species’ apart from four named exceptions (native species commonly kept in captivity). This protection of plague skinks continued even when these last four native species were granted full protection in 1996.
While it may seem farcical for an introduced invasive species to be legally protected, it did (at least in theory) provide some restrictions on the plague skink’s spread compared to if it had been left unprotected. Absolute protection means that it is illegal to catch, hold or liberate that species, and so from 1981 anyone who deliberately transported plague skinks around the country and released them was breaking the law.
Protection for the plague skink ended in 2010, when the Wildlife Order 2010 added ‘Rainbow skink (Lampropholis delicata)’ to the schedule of ‘Wildlife not protected’ under the Wildlife Act. However, it was immediately listed as an ‘Unwanted organism’ under the Biosecurity Act, making it illegal to move or release plague skinks, or offer them for sale.
Plague skinks in the Coromandel
Plague skinks had reached the Coromandel Peninsula by 1984, when they were first recorded at Waikawau Bay in the far north-east. They reached Coromandel town around 1993, and are now abundant there. More recently they have also been detected at Thames (2004) and Whitianga (2016).
My own experience of plague skinks near Coromandel is on the farm that my grandparents established at Papa Aroha, between Coromandel and Colville. During dozens of visits there since the 1960s, I had encountered only two lizard species on the property – a few shore skinks among the driftwood on the beach, and occasional copper skinks under rocks or logs further inland. Unless you went looking for lizards, you would be unaware that any were present.
That has now changed. During my most recent visit over Christmas and New Year, skinks were noticed scurrying for cover at numerous sites, and their identity as plague skinks was confirmed at three sites each more than a kilometre apart.
Should we be concerned?
Plague skinks occur at high densities and breed more rapidly than native skinks. They also occupy the same habitat and eat the same small invertebrate food as some native species (particularly the copper skink).
While there is not yet any research showing a measurable impact of the plague skink on native New Zealand lizards, there are several ways this could occur. In addition to direct competition, the invading plague skinks could carry new mites or diseases, and their dense populations may increase the exposure of native lizards to diseases already present, or support higher populations of predators.
Apart from any potential impact on native lizards, we have no information on the impacts of dense populations of plague skinks on native invertebrate communities.
Losing the indigenous
For most people, a lizard is a lizard is a lizard, and they are unlikely to recognise that the small brown skink that they have seen in their garden is an introduced invasive species. But the spread of the plague skink is just one more example of foreign species dominating New Zealand ecosystems.
We already live in a land where all our farm animals, pasture grasses, crops and timber trees are introduced. Most of the birds that urban-dwellers see are introduced and perch in foreign trees. The fish we catch with fly-rods in our rivers are introduced, as are the deer and pigs we hunt in the hills.
Children delight in trying to catch frogs and tadpoles (of three introduced species), with little chance of ever seeing a native frog. Will the same soon be the case with our lizards?
With thanks to Rob Chappell, Neil Fitzgerald and the Department of Conservation for information on the distribution of plague skinks. Much detail on plague skinks and their potential impacts is contained in Chapple, D. (ed.) 2016, New Zealand lizards.