August 2019

News From the Trap Lines

Data being collected is showing an significant increase in the number of rats caught in traps. There is also an increase in possums being trapped.

What We Can Expect - Early Ecological Research by Rowley Taylor with comment by Peter Hale

There are some interesting historical observations and accounts here.The full pdf can be sourced at the end of this summary.

You can draw you own conclusions as to the effectiveness of single trap lines targeting rats on the perimeter of large areas with no rodent control and whether any biodiversity gains are made.

“Hundreds of dead rats were reported from the shoreline or floating in Lakes Rotoroa and Rotoiti. This coincided with the germination of most red and mountain beech seed in the region. Seemingly, with the seedbank suddenly gone rodents had to search for new foods, or starve. Our autopsies suggested many were resorting to honeydew. At the rural Gowan Bridge store (near Lake Rotoroa) locals started buying rat poison in mid-October, sales peaked in mid-November, but poison was still selling well in December and there were still more rats than usual around in March 1972.

This rodent “plague” occurred over a wide area including the Lewis Pass, Maruia Valley, Inangahua, Buller Gorge and Nelson Lakes (BW Thomas pers. comm.; PJ O’Regan pers. comm.; pers. obs.)—it was by far the largest I have seen. During visits to Stewart Island and the West Coast Sounds in the 1870s Thomson (1922) was struck by the abundance of Norway rats “in regions uninhabited and almost unvisited by man”. On a wide stretch of mile-long shore in Patterson Inlet, Stewart Island, he found “the whole beach alive with rats which were feeding on the shellfish and stranded animals which the tide had left exposed”. When alarmed they ran to the shelter of the bush, “they were literally in hundreds”.

Such early immense numbers of Norway rats, also reported from Fiordland by Reischek (1888) and Henry (1901), were probably not the result of periodic heavy forest masting. Rather, they likely arose from an abundance of previously unexploited resources and a lack of competition and predation from later arriving ship rats and (in Fiordland) mustelids. Later developments The years 1971 to 1976 were ones of intensified rodent research in New Zealand, stimulated to some extent by the response of rat and mouse populations to the massive 1971 fruiting in both North and South Island forests (Daniel 1978; pers. obs.). A major Ecology Division study continued on the bionomics and diet of ship rats in the Orongorongo Valley near Wellington (Daniel 1972, 1973). Interest also increased in rodent parasites and the role of rats and mice in maintaining and spreading disease (e.g. Brockie 1976; Gibson 1972). Numerous island surveys expanded our knowledge of rodent distribution in northern New Zealand (e.g. Bettesworth 1972; Bettesworth & Anderson 1972), Fiordland (Thomas 1975), Stewart Island (Taylor 1975a) and at the Auckland Islands (Taylor 1975b). A further important impetus to research was Ian Atkinson’s (1973) reconstruction of the Spread of the Ship Rat in New Zealand. Then, with studies of the effects of rats on lizards (Whitaker 1973), tuatara (Crook 1973) and petrels (Imber 1975), we began to really sense the impact of introduced rodents on the New Zealand environment. This culminated in the historic 1976 symposium on the Ecology and Control of Rodents in New Zealand Nature Reserves (Dingwall et al. 1978)and further boosted research into rodent distribution, food habits, reproduction, dispersal ability, interspecific competition, interactions with other species and the steady development of eradication techniques now employed worldwide. Finally, when dealing with rats it pays to remember there are no cast-iron rules. Rodents are very clever animals, and the key to their control and eradication is to understand their life strategies and identify and exploit weak points. In this respect we have made amazing advances in the last 50 years –due mainly to a better understanding of rodent populations and behaviour, the development of second generation anticoagulant poisons, and improved baiting techniques. I have learned never to be surprised. click here

The Megamast

The Predator Free NZ Trust news contained two articles from Dr Graeme Elliott on the current megamast.

Graeme is a Nelson-based DOC scientist with more than 45 years experience working with endangered species. In the first part he describes what a mast event is and the timeline of the response of predators to this food bounty. In the second part he outlines what is necessary to try and protect vulnerable species on a landscape scale.

Julie Robilliard