A Murder of Rooks

From Southland to Northland, Regional Councils around the country are once again putting out the call for sightings of rooks, Corvis frugilegus, in their efforts to exterminate them.

The rook is a minor agricultural pest, on a par with the yellowhammer, so how did this bird become a target for extermination rather than control? How did this bird become an unwanted organism under the Biosecurity Act?

The rook is a black, hoarse–voiced bird about the size of a magpie which was brought to New Zealand from Britain between 1862 and 1874 to help control agricultural pests. Unlike many other European birds introduced at the same time, rooks spread very slowly at first. Even as late as 1970, they were largely confined to parts of the Hawke’s Bay, Manawatu, southern Wairarapa and Canterbury.

In the 1971 rooks were declared an agricultural pest in the Hawke’s Bay, largely because of the damage done to emerging crops.  Something like 35,000 thousand were shot, probably about half the population. Control methods were affective as by the mid 1980s estimates of rook damage went to almost nothing, as indicated by complaints received by the DSIR and Pest Destruction Boards.  Several authors noted that control measures resulted in the spread of rooks to other parts of the country. The recent campaign has further extended their dispersal from Northland to Southland.

Regional Council web sites make various claims about the destructive behavior of rooks, some of which belong to the realms of fantasy. The claims range from pecking out the eyes of sheep to the widespread destruction of crops and pasture, in spite of also admitting that 75% of the rooks diet is insects.  A pest destruction officer from the Bay of Plenty sent me an image of pasture uprooted and destroyed by rooks. From my experience, it was clearly pasture destroyed by grass grub which some bird, probably starlings, or maybe rooks, had uplifted, the very birds imported into the country to control grass grub. Regional Councils also claim that the rook impacts on native bird populations, a claim which is frankly ludicrous. The more realistic claim that rooks are a problem with emerging crops has been largely nullified as farmers now use seed coatings which repels birds.

So, what is going on?

The process by which an organism is declared unwanted and subject to eradication in New Zealand is obscure to say the least. It certainly appears to want to baffle the lay person.

The Biosecurity Act guides pest management in New Zealand. Its main purposes are to prevent new pests from entering the country and to manage pests that are already established here. Regional councils are primarily responsible for the latter. The Act enables Regional Councils to develop a pest management approach that is specific to the region’s needs and communities’ expectations. One of requirements of the Act is that pest control must be cost effective, so the yellowhammer, mustelids and rats, are too numerous and widespread to eradicate but the rook is apparently a viable target because of its limited numbers. However, with the plans to eradicate all pests under Predator Free 2050, this may change.

The public are allowed to make submissions on regional pest management plans but although many people have made submissions in support of the rook over the last twenty or so years, the submissions have been ignored. Farmers, such as Olrigg Station, wanting to protect the rook  because of their appetite for grass grub, have been threatened with prosecution and worse.

Where is the science in all of this? The experts on birds, the NZ Ornithological Society, are silent on the matter, possibly because it values its scientific objectivity too much to get involved in “politics”. However, I have perused their literature and there is nothing there  to justify the extermination of rooks.  Forest & Bird say they are "comfortable" with the Regional Council exterminating rooks.  

Horizon Regional Council, who seem to be the main protagonists in this campaign against the rooks, has involved Landcare Research but largely to determine whether extermination is a viable option and to determine the environmental fate and humaneness of DRC-1339, the toxin most commonly used for control of rooks at rookeries. DRC-1339 is an organochlorine, among the worst pesticides around.

The project to exterminate the rook has cost a considerable amount of money, a windfall to the pest destruction industry whose relationship with regional councils needs a closer examination. In perusing the voluminous amount of data on pest strategies on line, I have managed to glean that over a period of twenty years 2002-2022 at a cost of $60,000 a year the Wellington Regional Council proposes to eradicate the rook. Extrapolating this over the other regional councils, the cost has been astronomical, many millions.

Now in looking at all this, the logic somehow escapes me. Is this the plan of some fanatic with a hatred of big black birds? Is it part of a fiendish plot to eventually eliminate all introduced birds? Is it an experiment to see if it is possible to exterminate a pest species? I think the public has a right to know.

New Zealand's avifauna, native and introduced, is far from numerous. European birds have now been here for about 150 years. Following the Darwinian scenario of the finches on the Galapagos Islands, a very small number of birds, carrying just a portion of the species genetic potential, will over time change and radiate to fill the ecological niches which are on offer. Isolated from their parent birds, European introduced birds, will in time become truly our own and probably quite different from their European counterparts, unlike Australian introduced birds whose genetics may be boosted by birds continuing to come across the Tasman.  

Postscript:  After a Twitter exchange with Greater Wellington Regional Council @greaterwgtn over whether or not they had a scientific report to support their campaign for exterminating the rook, they passed me along to the Ministry of Primary Industries @MPI_NZ who revealed that there was either no such report or it had been lost. They were categorised as a Small Scale Management Programme at the request of Regional Councils. I am now in the process of refering all this to the Ombudsman.