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Proceedings of the First Symposium on Marsupials in New Zealand

Topic 8: Effect Of Animal Control On Non-Target Species

page 261

Topic 8: Effect Of Animal Control On Non-Target Species

CUMMINS. One of the topics suggested for discussion is the effect of control methods on non-target populations.

FALLA. The Nature Conservation Council of course is known to have recently expressed interest in finding out as much as possible about the effect of our accelerated possum control programme on non-target populations. Having found it difficult to get anything more than a somewhat patronising assurance from control bodies that the matter was being looked after, there has not been what Council would have regarded as a very specific assurance that everything possible was being done. Now I think it could be said that there is a feeling throughout the community that the non-target effects of a massive and fairly indiscriminate application of any toxic agent is a matter of general concern. There may be some inarticulate sections of the human population who cannot do very much about it. This is why the Nature Conservation Council has taken the matter up.

In this symposium there have been only two references to non-target populations; the first was a reference in relation to the Haupiri study of the N.Z. Forest Service, though no details were given as to how checks were to be made of the non-target effects; the other reference was by Dr Cook to the effect that there was a marked increase in bird populations following a control operation. Having been an ornithologist for over some 60 years now, studying bird populations throughout New Zealand, I was immensely interested to hear that there was a place where this has happened. My own experience has been completely the reverse through the whole of that period. Following any sort of extensive poisoning operations there tends to be a depression in the bird populations which is probably due in some cases to a depression in insect populations. Now admittedly my active field work was in the cyanide era and I'm perfectly certain that cyanide was basically responsible for a severe depression in a whole range of insect fauna and therefore indirectly on the insectivorous birds.

As recently as last year this was the experience of Dr Douglas Flack who while working on one of his study species in a mainland province, (as distinct from his work on island populations), found so much frustration that he practically had to give up his study of robins. Every time his work was in an area where there had been pest control his study population of robins had declined. I asked him if before he left New Zealand he would put this in page 262 writing and say something about it publicly because it is not any use at second hand; I am therefore quite sure that Dr Flack will have something quite substantial to say about his experience throughout parts of New Zealand in the last 4 or 5 years.

So we would very much appreciate some explanation of how Dr Cook's bird population explosion was monitored, who monitored it, how they did it, and what particular species showed such a very spectacular rise after a heavy dosage of 1080. Now admittedly there are not very much data on which this can be assessed but it would be helpful if you could get some sort of information as to how these checks are done. We know that the Wildlife Service have been called in at Karioi state forest and other areas, and a report is being compiled citing bird deaths that occurred after 1080 airdrops.

CUMMINS. We do seem to have a live grenade thrown into the ring. I wonder who is going to pick it up.

SPURR. As part of our next four years research, the Forest Research Institute is starting a major programme of investigating deaths in non-target species resulting from poison operations.

COLEMAN. To expand on Dr Spurr's comments, over the next 4 years 1/11 of our scientific effort will go into the effects of 1080 on non-target species. When you consider we have a watching brief over all the noxious animals, our ungulate research officers are looking with a rather jaundiced eye at the number now being pulled into possum research, including the non-target species work. So we are treating this seriously. I would like to take up another two points. In the original Forest Service trials of 1080 detailed surveys were made for bird carcasses; from memory the blackbird Turdus merula was a common species that was identified, but very few other dead birds were found. Secondly, my personal view is that we must establish our priorities. If we are going into sheep farming industy and keas Nestor notabilis attack our stock then the keas are destroyed. If we are to grow pine trees as long as there are adequate reserves, then pine trees in these areas are key issues and other things must become secondary to this.

HAMILTON. I would like to know if anyone is looking into the problem of where 1080 is going after it passes through the possum, or otherwise. There is an page 263 appalling amount distributed, one lethal dose per square metre. It must be going somewhere - is it retained in the soil or ending up in say insects or birds?

COLEMAN. In terms of leaching of 1080 into the soil-forest humus, this is well documented by Dr Andrew Peters' work. I do not know about the insect-life.

NELSON. The Agricultural Pests Destruction Council is supporting research by Dr Walker of Canterbury University on the breakdown of 1080 by microorganisms.

CROOK. We have heard two quite contrary views about the question of poisoning non-targetbird species, one by Sir Robert Falla, the other by Dr Coleman. I am not aware that Dr Flack had trouble with poison operations and robins, despite my working with him for several years. On the other hand not only blackbirds were affected. The work of the Wildlife Service in this area is still in a formative stage, which is one reason the Service has not taken an active role at this symposium. In Karioi state forest in the winter of 1976 there were 158 dead birds recovered from the poisoned forest area of which 36 were blackbirds and 66 were chaffinches Fringilla coelebs; the rest included 14 robins Petroica australis, 7 pied tits Petroica macrocephala and 18 whiteheads Mohoua albicilla. Now the 1080 poisoned carrot was dropped at Karioi at 40 kg/ha. and included some raspberry-flavoured lure. I think even if 1080 does kill birds we must examine whether this is significant or not in terms of the bird fauna - this is still very much an open question.*

PRACY. In relation to the effect of 1080 on birds, I was in charge of the initial Forest Service trials. After intensive searching I think the sum total in 5 trials was 3 blackbirds. Regarding Karioi forest, in 1976 there was an exceptionally severe winter. This was also the problem in the Wairarapa where there was 16,000 acres (6475 ha) of ground and aerial control; page 264 for 20 miles (32 km) outside the poison area you had a natural mortality of birds. No one is going to tell me these birds were flying 20 miles (32 km) from the poison zone and then dying. Winter conditions can have an adverse effect on bird populations, especially severe frosts.

Secondly, when you talk about toxic sowing rates of 40 kg per hectare, you must not forget that in some of these areas 20 kg per hectare of pre-feed is put out also. Any good field operator will make careful assessment of the country for sowing rates, such as in a situation like Karioi. It is a completely ludicrous sort of a situation to go and sow 20 kg per hectare of pre-feed and condition birds to a non-toxic bait, then in a week or ten days to put on 40 kg per hectare of toxic material. When you condition birds ahead on a high pre-feed rate and you have a high toxin sowing rate, then you are just asking for trouble. And this is a field problem. You cannot stand on a road, look into the hill country and say "I'll sow that with 40 kg and 20 kg pre-feed" and that's that. It does not work that way. You must do a field assessment.

Let me make our problem quite clear - there are forest and habitat types for which you get down to 12 lb an acre (2.2 kg/ha) of toxin and no pre-feed; likewise there are areas where you can use 15–20 lbs per acre (2.8–3.7 kg/ha) and probably 5 lb (2.8 kg) pre-feed. Again in extremely dense cover you need maybe 30–40 lbs per acre (5.5–7.3 kg/ha) of toxin. Sowing rates depend on habitat type and condition, physical condition of the animal and availability of food.

McLEAN. Regarding the birds, Mr Chairman, I wonder if anyone has ever thought of the damage the possum is doing to bird-life. I have spent 20 years in the Wairarapa and then went away for 4 years. I am amazed at the fall-off in bird-life throughout the Wairarapa in general while I was away. There has been practically no poison or 1080 used there during that time. I personally believe that the possum is a deciding factor in the fall-off of our bird-life.

WODZICKI. Mr Chairman, many of us here agree with what Sir Robert Falla has to say. I wish to point out that figures on bird casualties alone may have little value. We have methods to assess bird populations in New Zealand forests in terms of densities, which are far more meaningful. Also if you know the population dynamics of a species, then if you poison you can determine whether the population will recover, or whether it is doomed.

page 265

GREEN. There has been absolutely no criticism of the vast amounts of insecticides and pesticides that the agricultural industries are putting on our pastures throughout the country, and I am sure that per annum this is having a far greater impact on insect populations compared with 1080 drops, or with amounts of cyanide. I would sincerely hope that appropriate investigations are carried out to see what effect the massive use of these chemicals is having on our flora and fauna. Regarding the control operation at Karioi where last winter 158 birds were killed, I believe, and I stand open to correction, that the particular poison operation used a raspberry lure which is usually not done, particularly in most Forest Service operations. It seems that this raspberry lure is attracting a lot of birds and is therefore probably one of the major factors responsible for the deaths.

GIBB. Mr McLean mentioned there are fewer birds in the Wairarapa than there used to be. I think we might both be getting a bit deaf you know! Regarding the methods of measuring bird populations mentioned by Dr Wodzicki, one can measure bird density in a pine forest if one devotes enough time to it. It is not easy and it takes much experience. It certainly cannot be done in anything other than a small-scale research operation. In Ecology Division we have tried to develop methods of monitoring bird populations, primarily in beech forests and in conjunction with the Wildlife Service. Even after many trials I would be surprised if these methods would reliably detect changes before and after a poison operation of less than, say, 30 percent. These measures are pretty crude and are not accurate. They may be sufficient for use as repeated measurements on large blocks of country to give an index of bird numbers in different forest types. I do not think they suffice as a measure of bird populations before and after poisoning operations.

YOUNG. I would like to ask Sir Robert Falla that, given there are plans to review 1080 control, who would be responsible for implementing any trials. Would this be done under any moderation, or is it to be left again for the different groups now in the business to make their own estimates?

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FALLA. We have not received any indication as to who will accept the responsibility for the very considerable amount of further routine research and assessment. One basic problem is that the funding is very much directed to the agency that is dealing with an economic problem; assessment of such things as the impact on non-target species does not appear initially to matter very much.

There seems little chance of alternative funding, unless from an endowment fund without any tags or commitments. As far as I know the universities through the Universities Grants Committee is the only source of mounting research programmes of this kind.

It is good to hear from the N.Z. Forest Service, the Agricultural Pests Destruction Council and the DSIR, that there could be more research on particular economic aspects, but there is a limitation even there. The most the Nature Conservation Council expects to do, having tapped available expertise and information, is to present to Government (as is its statuatory duty) recommendations on 1080 which will include lines of research.

ANONYMOUS. There seems to be a gap between what this symposium is discussing as research, and what might be simply described as good servicing of the management people. I heard from a Pest Destruction Board Supervisor who was surveying the scope of his job and possum eradication. His comments echoed the sentiments "If I had any brains I wouldn't be in this job". Again, Les Pracy commented on the necessary understanding of the field operator in carrying out an air drop as it proceeds across different habitats over hill and down dale. There is a different requirement needed in each section of the air drop zone; because of a lack of study and documentation the thing is put down as 40 kg per hectare full stop. So there is a gap from the research level down to the actual carrying out of the control operation. It would seem people like university departments could assist by putting either students onto the problem, or control agencies could give employment to graduates to try and fill this gap.

FRY. I would like to comment very strongly here - that everyone in the field who is concerned with attempts to control is very disturbed at the lack of control they're getting, and we would like research directed to obtain better control.

* further information is to be found in the following reports:

BATCHELER, C.L. 1978. Report to Minister of Forests and Minister of Agriculture and Fisheries on compound 1080, its properties, effectiveness, dangers, and use. N.Z. Forest Service, Wellington.

HARRIS, G. 1977. Report on the use of sodium fluoroacetate (1080). Nature Conservation Council.