WILD LIFE IN NEW ZEALAND

Otago Witness, Issue 3414, 20 August 1919, Page 61

WILD LIFE IN NEW ZEALAND

" By the Hox. G. M. Thomson, F.L.S. No. 56.—THE SONG THRUSH. Nelson was the first part of New Zealand to introduce thrushes from the Old Country, the local Acclimatisation Society having received and liberated five birds in 1862. They promptly disappeared, and none were seen for many years, when they began to reappear. The probability ia tlxat the earlier lot failed to establish themselves, and that later on immigration from /some adjoining part stocked the district. Otago followed suit in 1865, and in seven years had introduced 145 birds. There was no mistake as to the determination of the Otago settlers to have their favourite song-bird—the mavis—estab-'' lished in this country.- It shows, too, the hardiness of this species in confinement, that of 48 birds shipped in 1869 in London by Mr J. A. JEwen, and put in charge of Mr R, Bills, every one was landed alive in Dunedin. They established themselves at once. The Canterbury Society landed 36 in 1-865, and a lot more in 1868 and 1871. The annual report for the latter year states that " they have not increased as well as expected, and it is much to be feared have been killed by cats." The large amount of native bush hi the neighbourhood' of Dunedin was, no doubt, more favourable for their increase and protection than the comparatively open country of North Canterbury. In 1875 a further lot was brought in by Mr Bills, some of which were sold, and others liberated in the Christchurch Gardens. It was, however, more than 20 years before thrushes were thoroughly established there. The Auckland Society introduced 30 in 1867, and 95 in 1868. They established themselves at once. The Wellington Society imported eight in 1878. In the, Otago Society's report for 1881 it is stated that "thrushes, we are glad to find, are becoming more plentiful in the neighbourhood of Dunedin. They are blamed for destroying fruit." Apparently this, was thought by the writer to be a habit specially acquired in their- new habitat. At the present day thrushes are found from one end of New Zealand to the other in enormous abundance. They are responsible, along with blackbirds, for continual and serious depredations in orchards. Before their introduction fruit of all kinds could be grown in the open, but as they began to increase it became impossible to grow small fruit, especially, without protection. Netting has had to be resorted to by all while in large" orchards guns, supplemented by owls, cats, crippled hawks and gulls, have to be employed to keep 'the depredators at a distance. Against this damage must be placed the fact that they eat a great quantity of insect life, and of land mollusca, snails especially. In New Zealand, as in Europe, earthworms are their favourite food, but these all belong to introduced species. Drummond quotes a Hawke's Bay correspondent as follows:—"For about 130 days in the year, until well into January, a thrush has comedo my farm morning after morning. Over an area of about 300 square yards he collects worms, and takes them to his mate, sometimes carrying two or three at a time. I have watched hinr" frequently, and from 7.30 a.m. to 8 a.m. he takes about 50 worms. I think I underestimate it in putting it at 200 worms a day." Mr >Philpott writes me (1918) t " The song-thrush does not appear to penetrate far into the big forests, nor to spread into unsettled areas. In the coastal forest of Fiord County they are seldom to be heard, though plentiful enough about the settlements of Tuatapere and Papatotara. Nor does the bird favour the mountains; I do not think I have ever heard one above the bush-line (about 3000 ft). They are certainly absent along the upper limit of the Titiroa Forest (Hunter Mountains), and I have no record of meeting with them on the Longwood tops or the Hump." The effects produced on the native and introduced vegetation of New Zealand by the introduction of thrushes and blackbirds have been very marked in at least one respect. The indigenous flora of New Zealand contains an exceptionally high proportion of plants with succulent fruits, amounting to approximately 16.55 per tfcent. of the whole. In Australia about 9 per cent., and in Britain 5 per cent, "of the whole flora have succulent fruits. The introduction of fruit-eating birds, such as thrushes and blackbirds (which in the case of small fruits swallow them whole and so distribute the seeds, and in the case of large ones like plums and apricots carry them off to some distance where they can pick off the flesh and leave the stones) has led to a considerable increase in succulent-fruited plants. A considerable proportion of the indigenous birds of New Zealand are frugivorous, and it is their prevalence which no doubt accounts for the abundance of indigenous succulent-fruited plants. But the advent of the thrush and blackbird has increased this feature, though the former does not •penetrate far into undisturbed forest. For example, In the Town Belt of Dunedin, a wooded area in which the vegetation is protected from all grazing animals, j there has been a marked increase in the numbers of individual plants of fuchsia, Coprosma, Melicytus, Muhlenbeckia, and other berry and drupe bearing genera. Along wtih this, certain introduced plants, such as gooseberries,' currants, brambles, raspberries, Cape fuchsia (Leycesteria), but. above all, the elderberry (Sambucus) have spread through the native vegetation. The last-named plant in particular threatens to crowd out everything else, and a .considerable sum of money is spent each year in eradicating It. In many parts of New Zealand- tho blackberry and sweetbriar rose arc meat obnoxious pests, and thrushes and blackbirds are to some extent responsible for their spread.

This question of the distribution of succulent-fruited plants by thrushes and similar birds is of especial interest to naturalists in New Zealand, and I have summarised a good deal of the evidence which Kerner has given on the subject, especially that relating to plants which are now found in these islands. Thus in "Flowers and Their Unbidden Guests" (p. 29) he states that thrushes are made ill by the Phytolacca berries, which many other birds feed on without injury. Apparently the statement was based on the case of one individual bird, which was unwell after eating some of the fruit, for it is repeated again in his larger work on the "Natural History of Plants," where he says that "a song-thrush sickened after eating berries of Phytolacca." Now this plant (the common inkweed or poke-weed) is very abundant in the warmer parts of New Zealand, and Mr Cheeseman informs me that thrushes eat the fruit freely. Kerner also states that when the fleshy fruits of barberry, privet, prickly pear, and laurustinus, all of which have seeds exceeding 5 m.m. (one-fifth Of an inch) in diameter, were introduced into the crop of thrushes along with other food, the pulp passed into the gizzard, but all the seeds were thrown up. "The seeds of fleshy fruits which were greedily devoured were thrown out of the crop if the stones which they enclosed measured as much as 3 m.m." Now barberry is certainly spreading _in the bush reserves near Dunedin, and is distributed either by thrushes or blackbirds. Kerner also found that of the fruits and seeds which passed the intestines of the thrush no fewer than 85 per cent._ germinated. In most cases the germination was retarded in comparison with seeds not so treated. But in the case of a. few berries, such as barberry, gooseberries, and currants, it was hastened. The seeds of such plants as grow on richly-manured soil, such as docks and nettles, after passing uninjured through a bird's intestine, produced stronger seedlings than did those which were cultivated without such advantages. . The time taken by seeds to pass through the alimentary canal of a thrush was very short—half an hour in the case of the elderberry and three-quarters of an hour with seeds of currants. The majority of seeds took from one and a-half to three hours to perform the journey. Small smooth fruits of forget-me-not, and some grasses were retained for the longest period. . The habits of thrushes nave not altered appreciably in their new country. Their nests are of similar construction to those found in Britain, and there is' no change in the colour of their eggs. They commence to sing—in the South Island at the month of May—that is,_ at the commencement of winter. The earliest record I have is from Dr Brittin, of Papanui, who heard one in Christchurch on April 24. At one time I thought, with Sir Walter Buller, that albinism was on the increase among thrushes in New Zealand, but as the result of long observation I am compelled to think that this is not the case. Any thrush showing a t-ndency to develop white feathers seems to be a marked bird, not only by man, but by other birds, and even by thrushes, and such a bizarre specimen does not seem to have a happy time. The power of flight of the thrush is very great. The bird has ..found its way to the Chatham Islands, a distance of about 460 miles east-south-east of Oape Palliser, and it has become established there.