BIRDS, AGRICULTURE AND INSECTS.

Otago Witness, Issue 3614, 19 June 1923, Page 10

BIRDS, AGRICULTURE AND INSECTS.

Admittedly an arresting "heading.'’ Take away any one of the terms mentioned and we have an unbalanced caption. The three are interdependent. Settlers should appreciate this more than they do. In order to successfully cope with the attacks of insects upon vegetation generally, and farm plant lile m particular, it is well that farmers should appreciate certain simple entomological facts. Some insects are injurious at one stage of their life and others at another. It may be, as it is in most cases, the larval stage that is particularly harmful, yet that is no reason why the mature forms should not be destroyed, as they are the parents of the depredators. vV ire worms in the larval stage do endless damage, but so do the turnip moths. "Out the lot’’ is the safest plan. Nature is at hand to help the farmer. Ladybirds devour all kinds of plant-lice (aphides), and should never be destroyed. Then some insect lay their eggs in the larvie of Hessian flies, et-c., then hatches out and destroys its host—thanks be. Insectivorous birds should be encouraged, more especially the indigenous birds of New Zealand. All of our birds, except perhaps one, are helpful to mankind and his work. Yet what a little we do, as holders of this Dominion—for a space only,—to protect and encourage bird fife. Our attention has been directed to an interesting arti le or articles in the April and May numbers of the Journal of Agriculture entitled “The Relation of Birds to Agriculture in New Zealand,” written by J. S. Myers, B.Se., and Esmond Atkinson, Biological Laboratory, Wellington. We purpose quoting some illuminating extracts therefrom, but hope our readers will peruse the articles in full. They are worth it. Wc are concerned for the moment with the birds of the forest and their indissoluble interdependence. In the pregnant words of Mr L. MTntosh Ellis, Director of the State Forest Service, there is no other forest that he knows is so dependent on birds as that of New Zealand—in fact, “no birds, no forest. ” That statement 'n itself should weigh with our settlers who have recently experienced losses from flood waters, which in a, measure resulted from the reckless destruction of timbered country at their source. "The activities of birds in the forest may be discussed under three main headings : (1) Birds as the chief agents in keeping forest insect pests in check, (2) pollinators of the flowers of forest trees, (3) as distributors of the seeds of forest trees, and thus as agents in the establishment of forest. Now whereas in New Zealand birds are extremely important factors in all these three respect, in the great pine forests of the north of the Old and New Worlds, 2>ractically their sole service is in tlie war against insect pects. The flowers of ad the northern pines and of a very large proportion of the deciduous forest trees are pollinated (transference of the maie ceil or pollen-grain from the anthers to the receptive female*organ or stigma) by the wind, and the same agency is responsible for the carrying of the seed to new ground.” Our New Zealand forest is unique. It is estimated that of our forest plants 40 per cent, are windpollinated, 47 per cent, insect-pollinated, and 13 per cent, bird-pollinated. Although the percentage of bird-pollinated is comparatively small, some of our most important timber trees are included—such, for instance, as the rata-s, the pohutukawas, the puriri, and the rewarewa or honeysuckle, etc., and (although foreign to the country) the various kinds of eucalypts (gums). The writers of the articles from which our information is taken estimate that about 65 per cent, of what may be fairly called forest plants have more or less succulent fruit attractive to birds, and the dissemination thus of tree seeds by our native bird is not inconsiderable. It may he observed that the seeds of such trees would still reach the ground and he able to germinate there even if our forests were riuite birdless, Simply by the falling of these fruits to the ground beneath the trees : but it is asked, what husliman ever saw such trees as rimu spring up kindly, like, say, elderberry or sweet briar, despite there being ample seed on the ground ? The seeds must be, it appears, distributed, so that soil conditions are favourable for the development of the young plants. In Canada the Dominion Entomologist characterises birds as the most valuable insecticidal agency known, and yet civilisation spells death to our indigenous birds—tlie natural guardians of our forest wealth. It is a common experience to find in the bush (vide article) a tree riddled by the “liuhu” grub—the fleshy legless brown larva of a lajge beetle (Prionoplus reticularis). Such trees, whether dead or alive, have often considerable areas of softer material composed of sawdust and decayed wood supported by strong and resistant bands of

still sound timber. For extracting the hulius from such a log a man would probably choose a stout knife for digging into the decayed and softer portions, while those larval which were deeply ensconced in crevices of the sounder timber would he conveniently extracted by means of a long pair of forceps. The huia—now, unfortunately for Oiur forests, so rare that there is considerable ground for supposing it extinct—became so adapted to live ujion woodboring insects (and perhaps specially on the huhu) that it actually possesses the instruments suggested above as the most suitable for removing huhus from semidecayed trees. The huia is unique in that the shape of the beak—a character so constant that it is used extensively in the classification of birds is different in both sexes. The male’s bill is moderately short and very stout, while that of the female is long, curved, and more pliable. When a pair of these birds is working on a tree-trunk, such as described above, the male bird chisels away the softer material and literally digs out the larvae, while his mate inserts her long bill into the crevices and holes m the sounder wood, and deftly extracts the larvae that are lurking there. "The forest, with the insects which prey upon its various constituent plants, may he divided into several horizontal layers. In each of the particular insect habitats thus delimited we have a special army of birds confining its insectivorous energies to that one habitat. Commencing at the forest Boor—that crowded lumber-room of leaf-mould, decaying logs, ferns, mosses, liverworts, fungi, and such seedlings as can grow in this stratum — the insects of this layer may be divided into permanent inhabitants which spend there their whole life-history from egg to adult, and insects of which only a portion of the life-cycle is passed on the ground, the portion spent there being usually either that of the egg or pupa (resting stage) or both, and less frequently that of the larva. The forest-flooT is thus important from the economic viewpoint as a nursery for numerous insects which in their later stages will be destructive to the wood or leaves. The policemen of this bottom layer are preeminently the kiwis and the wekas—both flightless birds, which have suffered severely from ‘ civilisation.’ . . . The activities of these larger birds are supplemented by the North Island and South Island robins, feeders on the forest-floor. There are four other species which are practically ground feeders—viz., the North and South Island thrushes (now almost extinct) and the white-breasted and yellow-breasted tits, which are at the moment fairly numerous. Then we have the green wren, mostly relegated to the great beech forests, and the little rifleman, keen * hunters ’ along the forest floor.” To quote again: “The trunks of the trees and the larger branches, wit* their dense coating of mosses, ferns, and other perching-plants, and of creepers, form the chief hunting-ground for the rifleman, which wanders over every inch of the surface, probing with its awl-like slightly upturned bill into crannies an/1 cracks and into the damp recesses of moss cushions. The green wren in its search for tlie insects which constitute its food employs a similar method. The same scene of operations is shared by the saddleback, huia, and kaka, all of which obtain their insect pray from decayed wood and among the bases of epiphytes and masses of creeper. “The absence of overlapping in the hunting-grciunds of the great ecological groups into which we are here dividing the birds is rather remarkable. The rifleman, one of the most assiduous of the trunk-searchers, rarely by any chance wanders to tlie leaves and twigs, which are the beat of a third preventive corps, including in its ranks the brown creeper, the whitehead, the yellowhead, and the grey warbler. The close scrutiny of slender swaying terminal twigs necessitates not only a- patient assiduity hut also an added agility, which shows itself in the beautiful acrobatic performances of the three former species, and in the fluttering movement of the grey warbler in its efforts to take insects from twigs too slender to bear even its tiny weight. So tlie grey warbler, in thus taking prey on the wing and even occasionally chasing in the air moths which it has dislodged, affords an easy transition to the next group, which takes its food almost entirely in the air. Here come those expert fly-catchers, the pied and the black fantails, with their familiar habit of sitting alert on a twig, whence they dash after flying insects of various kinds, in the pursuit of which marvellous aerial evolutions, assisted by the fan-like tail, are gracefully performed, and the clicking of the tiny bristle-fringed mandibles as they snap on the prey is often distinctly audible. Possibly belonging to this class are the kingfisher, the shining cuckoo, and the long-tailed cuckoo, all of which are in the habit of darting on they prey from a position of vantage. Our kingfisher, unlike the English species, lives only to a relatively small extent on fish, . the majority of his food consisting of insects. The morepork, too, takes the whole bush as his hunting-ground and pounces on his prey —here again mostly insects from the air.”

The services of our birds to agriculture may be said to have been proved. It remains with New Zealanders to recognise more zealously their value in checking the increase of injurious pests, more especially the indigenous birds of tlie Dominion —all of the latter, remember, except possibly one, being either beneficial or entirely harmless. This is high praise indeed, but we believe that the writers of the articles from w’hich wo have quoted so freely have not exaggerated the position. “No birds, no forest ’

is a slogan indeed to stay the killing of anv of our native bird's if hut fully realised.