THE RELATION OF BIRDS TO AGRICULTURE IN NEW ZEALAND.

New Zealand Journal of Agriculture, Volume XXVII, Issue 2, 20 August 1923, Page 76

THE RELATION OF BIRDS TO AGRICULTURE IN NEW ZEALAND.

IV. THE INSECTIVOROUS SMALL BIRDS.

J. G. MYERS,

B.Sc., F.E.S., R.A.O.U., and ESMOND ATKINSON, Biological Laboratory, Wellington.

Among the bird inhabitants of any country there is a certain number of kinds of small birds which live entirely on insects and other small forms of life, without exhibiting any failings which might detract from the benefits they confer on agriculture. The present article deals with some dozen species of indigenous birds which in this manner represent a summation of all that is beneficial in bird-life so far as the war against insect pests is concerned.

In Canada there has recently been secured exact numerical evidence of the value of insectivorous birds (Dunstan, 1922). The white-marked tussock-moth (Hemer ocampa leucostigma S. and A.) is perhaps the worst pest of shade trees of all kinds throughout eastern Canada. In an investigation into methods of control it was found that “ the type of infestation in the cities differed greatly from that found in the woods — that is, under natural ■ conditions. In the cities periodic outbreaks, in which the caterpillars appeared as a veritable plague, seemed almost inevitable, but in the forest “ the insect was always present in small numbers, evenly distributed, but never in a state of outbreak.” To ascertain the cause of this surprising difference a year was spent in the woods, and the insect studied under natural conditions from egg to adult. The insect passes the winter in the egg stage, in masses deposited on the branches of trees and in crevices of the bark, and it was found that a very large percentage of these egg masses was searched out and destroyed by birds. In the cities, on the other hand, in the absence of insectivorous birds, the egg masses went almost entirely free. To obtain an accurate estimate of the part played by birds in thus helping to keep this pest in check, caterpillars and pupae (resting stage) were exposed' and watched. On the basis of these experiments it was demonstrated that over 80 per cent, of the eggs laid under natural conditions were devoured by birds. Nor did their work cease here, for over 11 per cent, of the caterpillars which hatched from the surviving eggs were discovered and eaten by the same assiduous searchers. Finally, of those caterpillars which escaped to spin their cocoons, 30 per cent, were destroyed by predaceous enemies, among which the birds were of no mean importance.

Such a case as this is typical of the activities. of the insectivorous birds. They are to be ranked among the greatest of those forces which tend to restore the balance of nature when a favourable set of circumstances has allowed the abnormal increase of any particular insect pest. Since the whole of man's relation to his environment may be summed up as an upsetting of the balance of nature and an attempt to escape the consequences, it follows that, the insectivorous birds must be ranked among his most efficient allies, without which, in the long-run, it is difficult to imagine how vegetation could survive.

There is now scarcely a country in the world which has not come to realize the importance to agriculture of its insectivorous birds. A. Godard (1917), writing in a viticultural periodical on conditions of vine-growing in France, pleaded for the protection of birds as the natural means of controlling insect pests. “ Outbreaks of pests in agriculture always coincide with the disappearance of birds, and this is more felt in agriculture and viticulture than in forestry, woodland birds being less liable to destruction.” In New Zealand, of course, the last remark does not hold, since forest-birds are here the most liable to destruction. “ In South Africa I to quote an abstract of FitzSimmons’s article in the South African Journal of Science, 1917] if the native birds were exterminated the human population would in a few years be reduced to a condition of starvation, while the ticks would destroy the domestic animals throughout the country. All natural checks to insect-increase, including parasites, diseases, and fungi, acting together with man’s fight against .the pest, are considered entirely.inadequate, without the aid of birds, to prevent insects from sweeping all vegetation from the face of the world.” These are strong statements, but the coldest logic can lead to no other conclusion.

In view of the spread of the cattle-tick in the North Auckland district the relation . between birds , and ticks in Jamaica is of the highest interest. Buckland (1917) states : “ The increase in number of Mar gar of us annulatus (Texas-fever tick) in Jamaica during recent years is synchronous with the decrease of insectivorous birds. Examination, of the stomach-contents of one bird showed the presence of seventy-four adult female ticks in an engorged condition. The Island of Jamaica is remarkably suitable for the breeding of cattle-tick ; experience has shown that all imported animals succumb to tick-fever. It is therefore essential that, in some way, the insectivorous birds should be encouraged to increase.” The subject will be resumed when the writers come to deal with certain introduced birds which destroy ticks in the north of New Zealand.

THE WHITEHEAD, THE YELLOWHEAD, AND THE BROWN CREEPER.

To come now to the insectivorous small birds of New Zealand, there is first a group of three species, the chief characteristics of whose beneficial activities have already been briefly indicated in the article on the birds of the forest (Part II of this series). These are the whitehead (Certhifarus albicilla Less.), the yellowhead (Mohoua ochrocephala Gm.), and the brown creeper (Finschia novaeseelandide Gm.)three birds fairly closely related and performing much the same functions in the zone and object of their insect-hunting. Both the whitehead and the yellowhead are small brownish birds somewhere about the size of a sparrow, but with pale-coloured heads, that of the whitehead is confined to the North Island forestrybeing white, while the corresponding colour in the yellowhead—a South Island species—is yellow. Both are frequently called “ bush-canaries.” In those bush districts where the one or the other is still to be found the whitehead .or the yellowheadaccording to the Island in which the district is situated — shows a habit of consorting in flocks or small travelling-parties, . keeping usually to the higher branches, flitting from twig to twig, and uttering incessantly a great variety of notes. When their curiosity is awakened

by the approach of a stranger the happy notes of industry and sociability give place, especially in the whitehead, to a harsh chattering cry, while the birds themselves descend to the lower branches to interrogate the intruder.

The brown creeper is smaller, with longer tail, and all the upper parts, nape, and back a deep and beautiful brown colour, contrasting somewhat sharply with the uniform whiteness of the .breast and underparts. This little bird is confined to the South Island, in a few areas of which its busy flocks may still be seen in almost any patch of bush. The three birds just mentioned are all essentially forest-birds, and their economic value is to be translated in terms of forestry alone. Their nests are placed almost invariably in the deeper bush, and it will scarcely be necessary to describe them here. It is surely obvious that any nest found in the depths of the forest should, by virtue of its position, be sacred from the attacks of those who, for reward, collect birds' eggs. The only legitimate prey of such collectors is the eggs of the housesparrow, which never nests far from settlement.

THE FERN-BIRD.

The fern-bird (Bowdleria -punctata Q. and G.), the next bird on our list, is one of those peculiar recluse species confined to a particular habitat—namely, . the densest swamp and the thickest bracken of the hillsides. In the latter locality it is less frequent than its name would imply. Unfortunately, the writers possess little exact information concerning the food habits of this bird, beyond the indisputable fact that it is practically entirely insectivorous. The almost total absence of many of the indigenous. swamp-birds, including the fern-bird, or “ swamprobin ” as it is called in the North Auckland district, from most of our phormium areas, coupled with the increased damage to the phormiumfibre industry by insect pests, renders it not; improbable that a little investigation into the case of the fern-bird would be of some economic interest.

THE PIED AND THE BLACK FANTAILS.

In Europe a summer scene would be manifestly incomplete without one or two birds of. the swallow family with their familiar flight, hawking for insects almost from ground-level to the upper atmosphere. The swallows and martins are among the most aerial of birds, taking their prey almost entirely-on the wing, and taking it, moreover, among such insects as mosquitoes, which inflict supreme annoyance on man. L. Pasqualis (1915) pointed out that “ so long as swallows are to be found in Venice there is no annoyance from mosquitoes, but when the birds migrate late in July these insects appear in swarms.” But the use of swallows in Italy was recognized long before this date. We are told (Balfour, 1914) that somewhere between 1790 and 1812 the Commune of Marsciano, Umbria, “ asked for a papal decree prohibiting the killing of nesting swallows for food because their destruction brought about insalubrity in the region, one reason being that the swallows feed on the small flying - insects so troublesome and hurtful to man and beast.” And this was before the relation between mosquitoes and malaria had been discovered. .

We in parts of New Zealand are troubled with numerous flyinginsects —mosquitoes and sandflies —and in the absence of all birds of

the swallow family from New Zealand it might be asked what agency we have here to prevent the increase of such pests to intolerable proportions. Such an agency is undoubtedly to be found in. the two species of fantail, the black (Rhi-pidura fuliginosa Sparr.) and the pied (R. flabellifera Gm.), which subsist almost entirely on flyinginsects captured in their native element by a succession of the most amazing evolutions, rendered possible largely by the large fanlike tail which has guided the choice of the vernacular name. Few birds are better known to New-Zealanders. It will suffice for a description to indicate that the black species has deep sooty plumage and is far commoner in the South Island, while the beautiful pied kind is widely distributed over both Islands.

The fantails are among the tamest and most confiding of birds, and it . is probably largely on this account that indications. are visible of a growing sentimental- regard for these birds, comparable to the affection displayed in England for the famous “ robin redbreast.” In the case of the fantails, for once sentiment is guided well, by the soundest if unconscious logic, and it must be obvious that such a sentiment is of incomparably more protective value to the birds concerned than all the legislation in the world. There can be few more efficient or betterequipped fly-catchers than the fantails. The bill is capable of opening to a considerable extent; and when so opened the sides of the gape thus displayed are fringed by an impenetrable hedge of stiff bristles, forming a fly-trap from which escape must be hopeless. .

During the summer months fantails show a decided predilection for the vicinity of water, where flying-insects and particularly mosquitoes are well known to abound. In such situations, frequently on a slender bough directly overhanging the water, the-fantails love to build their quite unmistakable .wine-glass-shaped nest — a structure of the very neatest workmanship, with shallow cavity often' lined with the shining down of young tree-fern fronds, and a tapering bottom, bound with spider-webs and resembling an inverted gnome’s cap. The small, whitish, somewhat shortly oval eggs are blotched with pale brown, chiefly towards the larger end.

When feeding their nestlings both parents work extremely hard, returning time after time with beak crammed full of minute flies. One of the writers observed last . season a nest of young pied fantails to which the parents brought no fewer than fourteen beakfuls in forty minutes, and this in spite of the presence of the observer, only a yard away, quite unhidden.

In winter, even more than in summer, the fantails show themselves in a considerable degree adapted to the alien conditions of settlement. It is no uncommon occurrence during the winter months for them to enter houses and other buildings, hawk systematically for house-flies through the rooms, and finally depart with the grandest nonchalance. We have even an authentic record of a fantail which was regularly let in at the front door of a dwellinghouse and suffered to depart when it had cleared from the premises its daily catch of flies. In Australia a fantail very closely related to our own is of the greatest use in that it destroys the sheep-maggot blowflies which constitute there such a serious pest to the farmer. Doubtless the same good service is rendered by our New Zealand species. »

THE GREY WARBLER.

We have now to discuss the grey warbler. (Maorigerygone igata 0. and G.), sometimes misleadingly known as “native wren,” but more appropriately called riroriro in imitation of its beautifully trilled note. Quite as much as the fantails, though in itself not so conspicuous, the little riroriro has adapted itself to the conditions of settled areas — some places to such an extent as to have become independent of the native bush. This adaptation has had two consequences : its services to agriculture other than forestry have been tremendously augmented, and its eggs have become liable to find a place in the collections of small birds' eggs bought indiscriminately by local bodies, &c. All may recognize without difficulty the grey warbler, with its sober grey plumage relieved by spots of white visible in the tail when it is expanded to aid the fluttering of this little insect-hunter at the tips of twigs too slender to support even its fairy weight. The nest is even

less mistakable, and should be confused with the work of no other bird in New Zealand. It is a covered structure hung from often a slender twig, though rarely pendulous. The opening in the sides, rather nearer the top than the bottom, is so small as barely to admit more than the tip of a finger, and is frequently shadowed by a small porch. The otherwise capacious interior is almost filled with the softest . feathers, in which lie the tiny pink-speckled eggs.

Few birds are so exclusively insectivorous’ as the grey warbler. At a period with even less apprehension of the true position than at present, when the colonists of Canterbury considered as pests all birds except the truly destructive ones they themselves had imported' from England, Potts brought forward as proof of the innocence of the grey warbler a nest which a pair had built embowered in a heavily fruiting red-currant bush. The parent birds had actually to brush aside the ripe fruit when entering the portal of their nest, yet not a currant was taken.

Strictly speaking, our riroriro is not a true warbler, but its differences from the warbler family are in no sense related to its insectivorous qualities.” Hence the following figures published in American Forestry, 1917, will be of interest as showing the. rate at which insects are destroyed by these birds and their allies : “ One palm-warbler was observed to catch insects at the rate of from forty to sixty a minute during a space of four hours, making a total 'of- nearly 9,500, while another species feeding on aphids (plant-lice) on a grey-birch destroyed eighty-nine in a minute and 3,500 in forty minutes.. The destruction of caterpillars is on the same scale, one warbler destroying twenty-two gypsy-moth {Dymantria dispar) caterpillars in fourteen minutes, another twenty-eight browntail (Euproctis chrysorrhoea) caterpillars in twelve minutes, and a third forty-two in thirty minutes.”

THE WHITE-BREASTED AND THE YELLOW-BREASTED TITS.

The two New Zealand tits which are really fly-catchers (Muscicapidae) — the white-breasted tit or miro (Myiomoira toitoi Less.) of the North Island, and the yellow-breasted tit or ngiru {M. macrocephala Gm.) of the Southare tame and familiar little birds which, nevertheless, are not very frequent in cultivated areas, though • both show a considerable liking for clearings on the edge of the forest. The males of both have the same colour scheme of plumage, with black upper parts, head and breast, and pale abdomen, but the Utter is white in the miro and yellow of varying shades in the ngiru. The females are greyish-brown with white under-parts, but may be recognized by their movements and build, which are similar to those of the males. Both species live practically entirely on insects, but they exploit a quite' different locus from the preceding species and a correspondingly dissimilar set of insects. A large portion of their food, as indicated in the article dealing with, forest-birds, is obtained from the ground, whither frequent darts are made from a position of vantage, in which the black beady eye is constantly alert. •

In winter both the miro and the ngiru occasionally frequent ■orchards and gardens ; but the writers know of no recent cases where nests have been built in such situations. The same remarks apply therefore to the nests of these birds as were made on those of the yellowhead and its relatives.

THE NORTH ISLAND AND THE SOUTH ISLAND ROBINS.

With regard to the North Island and South Island robins (Miro australis Sparr.), so far as economic considerations are concerned, we are almost compelled, on account of their great scarcity, to speak in the past tense. It is one of the great mysteries of the disappearance of New Zealand indigenous birds that the miro and the ngiru should have survived in such considerable abundance, while the two robins, so like in haunts, habits, food, and nesting-sites, should have become extremely rare. The moral is clearly this : that the decrease of the indigenous birds is not a topic on which any person is competent to express an opinion, but a scientific problem to be studied with all the methods of modern research.

the pipit, or ground-lark (Austranthus novaseedandiae Gm.).

In an indefinite manner every one knows “ larks,” but whether every one appreciates the difference between the little pipit and the introduced skylark is another question. It is, moreover, of the first importance that people should discriminate between the two, since the former is a wholly beneficial bird, while the latter is perhaps the most injurious bird in New Zealand which should never have

been introduced and for which very little good can be said. The pipit, or pihoihoi, which, by the way, is not a true lark at all, may be distinguished by the very conspicuous white outer tail-feathers, especially noticeable in flight, by its'much slenderer build and longer tail, the longer and slenderer bill, and, above all, by its familiar habit of rising from the ground just in front of one, flying a short distance and then alighting just ahead, where it walks briskly about uttering its cheerful note until the observer again approaches.

‘The nest, which is a much more substantial structure than that of the introduced skylark, is placed on the ground among the roughage of a pasture, in the drier portion of a swamp, or sheltered among the alpine herbage far above the bush-line on the mountain-side, as shown in Fig. 2. The eggs, as will be noticed, need never be confused with those of the skylark. They are often more rounded, but the chief distinguishing character is the heaviness and distinctness of the blotches of darker colour. In the skylark's egg these are smudged and less contrasted.

The food of the ground-lark consists almost entirely of insects and their larvae, some of the former of which it often snaps up on the wing. Small earthworms and occasional minute . seeds contribute to its bill of fare.

THE RIFLEMAN AND THE WRENS.

The last of the purely insectivorous birds to be dealt with are those small active short-tailed'birds popularly known as " wrens.” It should perhaps be mentioned that they are none of them true wrens, but members of a family or two families found nowhere else in the world. Of the three species still existing at the present day the rockwren (Xenicus gilviventris Pelz.) bears no relation to agriculture, since it is confined to the wilderness of rock above the bush-line on the mountains of the South Island the green wren (X. longipes Gm.), a very rare bird, renders some service to forestry . in that it is an everactive insect-hunter in the subalpine beech forests, where the ordinary forest-birds are quite rare. The rifleman (Acanthisitta Moris Sparr.), however, the smallest bird in New Zealand, occurs plentifully in beech forests in the North Island and throughout all forest in the South. It is easily recognized by its extremely small size, greenish colour, and slightly upturned awl-shaped bill, and by its habit of running in a very mouse-like manner up the trunks and large branches. The nest is placed in a crevice of bark or bank, or in a natural hole in tree or log. Frequently, when in living timber, the nest-entrance is so small that the tip of the forefinger can be inserted only by turning it sideways. Such was the case in the nest sketched and shown in Fig. 3. The nest itself is of the most irregular shape, and is suited to the exigencies of the selected cavity. The eggs are small and pure-white.

CONCLUSION (OF PART IV).

As was indicated in the opening article of this series, there are some birds which are beneficial, provided their numbers be not too great; with others a careful balance must be struck between the services they render and the damage they do. Tn the case of the insectivorous small birds dealt with in the preceding pages the only verdict must be one

of unqualified appreciation. The writers would stress that the annual loss'to this country through the damage wrought by insect pests is estimated at several million pounds, and that unquestionably the

greatest factor in the prevention of the increase of that damage to an extreme extent is the activity of bird-life, and particularly of such specialized insect-hunters as those just described.

REFERENCES. Balfour, A. (1914) : Birds and Malaria. Abstr. in Rev. Appl. Entom., ser. B, vol. 3, p. 45, 1915- ’

Buckland, J. (1915) : The Value of Birds to Man. Abstr. in Rev. Appl. Entom ser. B, vol. 4, p. 2, 1916.

Dunstan, Alan G. (1922) : The Natural Control of the White-marked Tussockmoth under City and Forest Conditions. Proc. Acadian Entom. Soo., No. 8, pp. 109-127.

FitzSimmons, F. W. (1917) : Our Native Birds—their Value to Man. Abstr. in Rev. ,Appl. Entom., ser. A, vol. '5, p. 354.

Godard, A. (1917) : Les Insectes Carnivores et la Vigne. Abstr. in Rev. Appl Entom., ser. A, vol. 5, p. 354.

Pasqualis, L. (1915) : Venezia e le Zanzare. Abstr. in Rev. Appl. Entom., ser. B, vol. 3, p. 64.