Hardly two men will agree as to the cause of the decline in the numbers of rabbits, and I will just state my theory for what it is worth. The grey rabbit, when first introduced, found himself in very congenial surroundings. There was abundance of food and shelter, and the ground was absolutely clean, never having been grazed by rabbits previously. These favourable conditions gave a tremendous filip to the vitality of the rabbits and stimulated their powers of reproduction. They increased at a rate that I believe is not even approached in the worst infested parts of Otago to-day. No efforts at checking them had the slightest effect, and they passed over the country like a prairie fire. After a time the original conditions no longer existed. Food became scarce, the land was foul with rabbits, disease appeared among them, and their fertility decreased. No doubt improved methods of dealing with them hastened their reduction, but I firmly believe that the principal factor in their decrease was lessened fertility, due to the first great spurt to their vitality having spent itself. The decrease first became apparent in the colder and wetter parts of the country. The rabbits abandoned large areas and became concentrated in warm sunny spots. Even in these spots their numbers declined, and from many of them disappeared altogether. In the dry country which is more congenial to rabbits, fertility is still maintained, and may possibly be permanent. The rocky hills round Alexandra may be taken as ideal country for rabbits, and probably this area has suffered more from them than any other part of New Zealand. All known methods of rabbit destruction have had an exhaustive trial there, and have not succeeded. It would seem that in this favourable spot the vitality of the rabbit is not greatly impaired. It would be interesting to try if rabbits could be re-introduced into country where they once swarmed, but which they have subsequently abandoned. I believe that such an attempt would fail.

Opinions different to mine are very widely held. Most men claim the credit of having themselves cleared their ground of rabbits, and the official Rabbit Department staff possibly take the credit to themselves. I should like to believe that to me belonged the credit of having cleared my own place, but my experience leads me to believe that my efforts had little to do with it.

It must not be assumed that every one regards the rabbit as a nuisance. Many a successful farmer of to-day got a start as a rabbiter. The killing of rabbits actually became one of the principal industries of the province. Their presence directly led to the subdivision of large estates, and may have been quite as effective in this direction as all the legislation on the subject.

The introduction of rabbits had a lasting effect on acclimatisation generally. Before their advent partridges and pheasants had become numerous, but they have entirely disappeared in Otago. In the effort to cope with the rabbits, the country was annually sown with poisoned grain. This had a disastrous effect both on native and imported game. Had rabbits not become a nuisance, it is unlikely that weasels and other vermin would have been introduced. These animals are largely responsible for the decrease in the numbers of native birds, and also make the successful introduction of new varieties more difficult.

The initial difficulties in getting rabbits introduced, the terrific success that at last crowned the efforts made, the unexpected ruin and destruction which they caused, and the gradual return to normal conditions, makes the history of their introduction one of the most interesting in the annals of acclimatisation.

Mr H. B. Martin in 1884 states that in various parts of the Auckland district the rabbits have become almost or quite extinct from natural causes; tuberculosis was also believed to be present in the Wairau Valley, where the rabbits were beginning to decrease before the present Act was in force.

In a discussion which took place in the Legislative Council on 4th July, 1883, the Hon. Mr Chamberlain said that rabbits were formerly numerous on Motuihi and Motutapu, and on Flagstaff Hill, but they had now become extinct.

Mr Edgar T. Stead, writing me as late as 25th July, 1919, informs me that:

in the Wills Valley and the Upper Haast, to the north of Lake Wanaka, the rabbits were at one time,-say ten or twelve years ago,—absolutely swarming. When I was there six years ago I was told that the rabbits were completely gone from the Wills Valley, and I personally observed that they were leaving the Haast. On the flat below the Burke hut there was still a fair number, but above that on the open stretches of river flat there was not one, though there were deserted warrens in all suitable localities. There are many places in Canterbury where rabbits have become scarce in the last ten or fifteen years,―more places still where the case is vice-versa,—but, as you remarked in your paper, there were only some races of rabbits that spread badly, and we do not know that the above-mentioned places were inhabited by the virulent races. In the Haast River case we do, for the rabbits had spread over the range from the famous Central Otago stock. It is quite possible that the country going "rabbit-sick" is only part of a cycle, but the subject is well worth investigating.

In the House of Representatives on 1st August, 1883, Captain Mackenzie said that a competent authority assessed the actual loss to the Colony through the Rabbit Plague at £1,700,000 a year. Mr W. C. Buchanan said that the loss for the past ten years was assessed at ten millions sterling. The question of importing a disease from the Falkland Islands was discussed at the same time.

I was at one time under the impression that in this new country, where the causes which kept them in check in their original home were wanting and there seemed to be nothing to arrest their development in any direction, there might arise new varieties of rabbits with modified habits. Particularly did it seem likely that colour variations would thrive unchecked, and the traveller passing through certain districts in Central Otago is certainly surprised at the number of

conspicuously coloured animals to be seen. Mr W. H. Gates of Skippers writes me (April, 1916): "As for colour they are of all colours;-grey and white; tan and white; grey, with a black ridge down the backbone; and buff." Other observers speak of the prevalence of black, black and white, and yellow rabbits. But Mr R. S. Black of Dunedin, the largest exporter of rabbit-skins in the Dominion, informs me that while they are of all colours, 95 per cent. of the skins exported are grey. The other colours appeal more to the eye, but they are not so abundant after all. That the rabbits of aberrant colours should survive is not to be wondered at, seeing that in this country there are no foxes, and neither hawks nor owls large enough to tackle a full-grown rabbit. The common harrier-hawk takes a considerable toll of young rabbits, but it is quite unable to keep them in check. In many districts wild cats live mainly on rabbits.

Mr Yarborough of Kohu Kohu tells me (August, 1916) that rabbits became quite common in a district near Kawa Kawa (at the head of the Bay of Islands) many years ago. Recently they have reached the eastern side of the Hokianga River, and it is not unusual to see them occasionally. Then he adds this interesting statement:

I have never heard of any rabbit burrows, as they appear to breed among the rocks and roots of trees. They do not seem to have crossed yet to the west side of the Hokianga River. No complaints have been heard of devastation done by them, and it seems to be doubtful if they would thrive in either our clay lands, or in volcanic areas.

The comparatively heavy rainfall of Hokianga, amounting to some 60 to 70 inches per annum, has no doubt a good deal to do with the comparative scarcity of the rabbit in this part of New Zealand. They are, however, not uncommon near Kaikohe, and do make small burrows1.

Effect of Rabbits on the Country and Native Vegetation. The economic waste caused by the vast increase of rabbits in New Zealand is incalculable, and certainly represents a loss in the stockcarrying capacity of the country which probably runs every year into millions of pounds. It is not only that they eat up food which would support some millions more sheep than are at present reared, but they destroy large areas of country, and yield very little return for the

1 One curious effect of the recent great war has been a phenomenal increase in the price of rabbit-skins. I have not been able to ascertain yet what effect this is having on the rabbit question in Otago, but by the end of 1919 it has become quite impossible to get rabbits for the table. At a sale held in Dunedin in December, 1919, the prices received for skins of winter growth ranged from 155d. to 274d. for six skins; that is to say, that the highest quality of super-does, as they are termed, brought 35. 10d. per skin!

Since this was written prices have altered greatly. In June 1921 the best skins were fetching about 74d. per lb., or from 8d. to 1/- per skin.

damage they do. The annual export of approximately 3,000,000 rabbits valued at about £70,000 and of some 8,000,000 skins valued at about £115,000 is all the return they give, but it only represents a small proportion of the dimensions of the pest. In all parts where rabbits abound, their destruction entails a heavy expense on the occupiers of the land. There are no data available anywhere to enable one to estimate how many rabbits are destroyed every year, but far more are killed by phosphorus than by trapping. The latter method alone furnishes any statistical data, the former is an unknown quantity, but it represents a very large figure.

Probably the most ghastly exhibition of the work of rabbits is to be found in the grass-denuded districts of Central Otago, parts of which have been reduced to the condition of a desert. It is improbable that this state of affairs could have been brought about by rabbits alone. Before their advent, the runholders who had possession of the arid regions-in which the rainfall probably averages 10 to 12 inches annually, and certainly never exceeds 15 inches-were doing their best to denude the surface of the ground by overstocking with sheep and frequent burning. The latter was resorted to because many of the large tussock-forming grasses—especially such as the silvertussock, Poa caspitosa-yielded coarse and rather unpalatable fodder, but after burning the tufts, a crop of tender green leaves sprung up, which were very readily eaten. Unfortunately the burning not only got rid of most of the coarse growth of the tussocks, but it also swept off the numerous bottom grasses which occupied the intervening spaces, such as Agropyrum scabrum, Danthonia Buchanani, Danthonia semiannularis, Triodia Thomsoni and Festuca ovina, which were the mainstay of the depasturing flocks. Even before the rabbits arrived the work of denudation of the grass-covering had been proceeding apace through the causes mentioned. Thus Buchanan, writing in 1865, said: "it is no wonder that many of the runs require eight acres to feed one sheep, according to an official estimate." Mr Petrie thought this an unduly severe estimate, "as in the mid-seventies the sheep-runs of Central Otago were reputed to carry at least one sheep to four acres, and the majority of them carried one sheep to three acres or somewhat less."

Mr Petrie, who reported to the Department of Agriculture on the grass-denuded lands of Central Otago, knows more about this subject than anyone else, and I quote him at some length:

Before the rabbit-invasion began the hill-slopes carried a fairly rich and varied covering of tussock and other grasses, and, except on the steeper rock sun-baked faces, had not been very seriously depleted even in the early nineties. The earlier stages of this depletion may now be seen in

several of the Central Otago ranges, as on the spurs of the Rough Ridge and the Morven Hills districts. The northern slopes of the spurs are almost, in many instances entirely, bare of grass, while the southern shaded slopes still carry a fair amount of pasture. The grass covering generally stops abruptly at the bottoms of the valleys, even when these are not worn into water-channels. The vastly greater depletion of the pasture on the northern slopes is easy enough to understand. They are more exposed to the sun and to the frequent violent parching north-west winds; they lose their covering of snow earlier in spring than the southern slopes, and are thus more closely grazed at a critical season for the pasture; and sheep at all times show a preference for feeding on the warmer sunny slopes. When the pasture on the exposed slopes fails, that on the shaded slopes has to feed all the stock that is about, and unless the stocking is reduced to meet the new conditions the remaining grasses are sooner or later eaten out. The desert, with all its problems, is then established.

In this account of how the desert conditions have arisen, Mr Petrie refers only to sheep, because it is the loss in sheep-carrying capacity which is so serious, but later on, after describing a typical specimen of the country, and showing that in inaccessible situations a considerable variety of fairly vigorous grasses live on, he adds:

"This is one of the facts that go to indicate that the extermination of the grasses in this desert country is mainly due to eating out by overstocking, rabbits as well as sheep being included among the stock carried." "The desert and the greatly denuded lands are not wholly destitute of vegetation. In most of their lower areas greyish, flattened, firm, nearly circular patches of scab-weed (Raoulia australis and R. lutescens) are thickly dotted about the bare ground. Though otherwise useless, these moss-like composite plants help to keep the soil from being blown or washed away, and when old supply, in the decayed centres of the patches, spots with some amount of humus where grass-seeds can more readily settle and grow." These plants are never eaten either by sheep or rabbits.

In regard to their effect on other native species of plants Mr Petrie writes to me in a letter of 1st May, 1916:

I know that rabbits have done much to reduce the abundance of the Otago Spear-grasses (Aciphylla squarrosa and A. Colensoi chiefly), probably during times when the ground was covered by snow. When I first visited inland Otago (1874) Aciphylla Colensoi was most abundant. In riding about it was almost impossible to deviate from well beaten tracks or roads, because the spines pricked the horses' legs and feet. I know of no evidence that sheep would eat fairly full-grown Aciphylla leaves, but young plants must be more or less eaten both by sheep and cattle (as well as by rabbits). Several species of Celmisia, notably C. densiflora, have been greatly checked, and C. densiflora almost exterminated.

Dr Cockayne is now (1921) engaged on an exhaustive investigation. Captain F. W. Hutton writing me on 23rd March, 1892, said:

As to the extermination of the Wild Spaniards (Aciphylla), I believe