THE RELATION OF BIRDS TO AGRICULTURE IN NEW ZEALAND.

New Zealand Journal of Agriculture, Volume XXVII, Issue 1, 20 July 1923, Page 13

THE RELATION OF BIRDS TO AGRICULTURE IN NEW ZEALAND.

III. THE LARGER FRUIT- AND INSECT - EATING PERCHING - BIRDS {PAS SERES).

J. G. MYERS,

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

The first article of this series discussed briefly the general principles of economic ornithology, while the second dealt with the relation of the forest-birds to the problems of forestry in New Zealand.’ In this, the third article, it is proposed to commence a more detailed examination of the New Zealand birds from an economic standpoint, to discuss the pros and cons of each species, , and, having decided which are beneficial and which injurious, to point out in a simple way how to distinguish friends from foes.

This is the more necessary since, although most country-dwellers have a fair knowledge of the commoner birds, the nests and eggs are much confused. ' Some agricultural associations, acclimatization societies, and local bodies make a practice of paying for “ small birds’ ” eggs a practice in which serious lack of discrimination is exercised with regard to the accepted eggs. Thus school-children are actually encouraged to take the eggs of beneficial indigenous birds . in their haphazard birdsnesting, in mistake for those of injurious introduced species. We know, for example, of no society which discriminates between the eggs of the native pipit or ground-lark and the imported skylark, yet the former is wholly useful and the latter almost entirely destructive.

There exists, also, at the present time in New Zealand no book of any kind which deals with indigenous and introduced birds alike and affords means of distinguishing them. In the following pages the present state of our knowledge on all these matters will be summarized, but there must be years more of the most patient field observation before the material is available out of which a comprehensive manual can be built. '*•

THE NATIVE CROWS, HUIA, NATIVE THRUSHES, AND SADDLEBACK.

The birds will be dealt with in . order of affinity, and at the head of the list, are placed the two New Zealand crows or kokakos — and South Island species respectively. In a work of this kind these, on account of their great decrease under the influences of settlement and their present resultant scarcity, need not detain us long. Their large size and soft bluish-grey plumage relieved by the striking wattles —blue in the North Island bird and orange in the —render them quite unmistakable ; nor is their rich organ-like note, once heard, likely to be confused with that of any other denizen of the New Zealand bush. It is needless to state that their influence in the forest, as agents in the dispersal of the seeds of trees, is wholly beneficent.

Still less to be dealt with in a work treating of'the present position in New Zealand are the huia and the two thrushes—North and South Island respectively. While it is uncertain that any of these are totally extinct, from an economic viewpoint they are of such extreme rarity that they are mentioned here only for the sake of completeness. The work of the huia was described in the second article. That of the thrushes, which, by the way, should never be confused with the introduced English song-thrush now so common, was comprised under the two heads of “ insect-eating ” and “seed-dispersing.” The sixth bird on the list, the saddleback, on account of its exceeding rarity may be dismissed in the same way.' Suffice it to state that just as the introduced starling leaves no stone unturned in its indefatigable search for insects of all kinds in cultivated and pastoral country, so this handsome indigenous starling subjected every crevice and cranny of tree and log to the same searching scrutiny. From the records of the past, and from what we know of the birds which still remain plentiful denizens of the forest, it is a safe assumption that all of these six species performed definite tasks in the economy of the forest which it would be fatuous to suppose can be as well accomplished either by the other remaining indigenous species or by the introduced birds, which are adapted only to the environment to which they were accustomed in their original northern home.

THE STITCH-BIRD, TUI, AND BELL-BIRD

In the next natural group, which comprises the honey-eaters, there are four birds—the stitch-bird, tui, bell-bird, and white-eye. The stitch-bird, though once very common, is now—like most of the group already mentioned—of extreme rarity, and is economically negligible. It was -at one time doubtless one of the most important of the forest-flower pollinators in the North Island (to which it is confined). Like all members of this group, though primarily a honey-eater, it feeds largely upon forest berries and insects as well. . The tui (or parson by far the largest and most conspicuous of the New Zealand honey-eaters,. is almost too well known to need description, but something must be said of its nest and eggs. The nest is wide in. to i ft. across) but shallow, and generally has rather an untidy look owing to its being made of interlaced fine twigs the ends of which project in all directions beyond the general outline of the nest. Manuka twigs seem to be the most often chosen when they are available. The shallow cavity is generally lined with the dark scales from young tree-fern fronds. The eggs — three or four in number—are very fragile-looking, and white or pale pink in colour, with a few scattered pinkish spots mostly at the larger end. They range from i in. to i|in. long by fin. or more broad." The value of the tui as a fruit and honey eater in relation to the forest has been spoken of in the previous article. No one familiar with the bird or its habits in the bush will deny this, but what may be again emphasized here is the work it does in pollinating .the many species of Eucalyptus that are now being planted everywhere for timber, and thus assisting their spread. It appears that the persecution of the tui is not confined to the bush itself, but that even those which venture to visit the gum plantations in settled areas are in some districts shot for gastronomic

purposes by Maoris. The decay of tapu and the spread of firearms have, generally speaking, turned the Maori into a serious enemy of all the forest-birds which are large enough for food.

The bell-bird, makomako, or “ mocker ” (an often-used corruption of the Maori name), is one of those native birds which, after showing a great decline in numbers, are now more than holding their own. The bell-bird, however, is much less familiar to most people than the tui, partly owing to its quite recent return to settled districts, and largely no doubt to its smaller size and less conspicuous colour. It is not much over 7 in. in total length (the tui being 1 ft. or more long), while its olive-green steely black and brown colour is very difficult to see compared with the glittering blues and greens of the tui’s dark plumage and the white neck-tuft which shows so strongly against it. The nest of the bell-bird, like the tui’s, is largely constructed ' of small twigs and moss, but is much smaller and neater, and is lined with feathers. The eggs are similar to those of the tui in texture, but are rather richer in ground-colour and in markings. They are nearly 1 in. long by almost f in. broad. What has been said of the good work done by the tui in the bush applies almost equally well to that of the bell-bird, while in many LwmriyWzs-planted districts the latter is the commoner bird of the two.

It should be mentioned here that there is often confusion as the result of the practice prevalent in many districts of calling the crow or kokako “ bell-bird," and reserving for the true bell-bird the name of makomako, "mocker," or even that final corruption "mocking-bird."

THE WHITE-EYE (WAX-EYE, SILVER-EYE, RING-EYE, OR BLIGHT-BIRD)

(Zosterops lateralis Latham).

The multiplicity of names bestowed on this little bird is sufficient evidence of its familiarity. Under one or other of these titles its olivegreen head and tail, grey back, and pale under-parts tinged very beautifully, with reddish, and, above all, the ring of white feathers round the eye, are probably well known to most people. Its numerous relatives are found over a large part of the eastern world and particularly in .Australia, where our ...own .white-eye.. also belongs, since, its colonization of New Zealand was apparently accomplished within the memory of man. It first appeared in this country, in the neighbourhood of Wellington, in 1856, and from that centre has apparently spread almost all over both Islands. In the first spring of its arrival, according to Buller, the tauhou, ■ or “ stranger,” as the Maoris called the feathered immigrant, was accorded a warm welcome on account of its energetic attack on the woolly aphis —then, as now, a difficult pest of apple-trees. Later on its attentions to cherries, plums, and other fruits led orchardists and the Press to revise their first impressions and to restrain the enthusiasm of their eulogy.

For the greater part of the year the white-eye consorts in twittering parties or flocks which work assiduously from tree to tree in their search for insects of all kinds. Like the birds which have been artificially introduced or “ acclimatized," to- use the expression of those who practise it, the white-eye seeks the wilder solitudes far less than do those birds which are peculiar to. New Zealand. It frequents gardens, orchards, and the vicinity of cultivation generally. In winter the small parties are considerably augmented, and large flocks then

repair • to the gardens of even . the most populous towns. Even in summer small travelling-parties may occasionally be seen in the most thickly populated districts. . ' , .

There are several birds, both native and introduced, similar to' the white-eye in size, but the nest of the latter (Fig. i) cannot be confused with that of any other bird in New Zealand. It is a basket-shaped structure, attached by the rim at' several places to two or more twigs lying more or less in the same horizontal plane. Though it may rest against twigs lying below .it, the nest is never dependent on them for its support, and may be therefore truly described as pendulous or hanging. It is very frail-looking, often showing the light through it, but owing to the skilful interweaving of the grasses, mosses, &c., of which it is built it is really a very strong structure. It is generally

lined with grass, with the wiry leaves of the grass-tree (Dracophyllum spp.), and very often, particularly near settled areas, with horse-hair. The eggs, of which three or four are laid in the nest, average under | in. in length. Their beautiful pale-blue colour combined with their small size distinguishes them from all other eggs found in New Zealand, except possibly those of the hedge-sparrow, which are larger and far deeper blue in colour.

The activities of the white-eye may be discussed under the following headings : (r) Pollination of flowers of trees, (2) dispersal of weedseeds and tree-seeds, (3) damage to fruit, and.(4) destruction. of insects. From the economic standpoint (1) and (4) can be adjudged as wholly beneficial, (3) as wholly destructive, and (2) as a mixture of good and evil, between which a fair balance must be struck in considering the treatment the white-eye should receive from the cultivator.

The first of these activities has been dealt with generally in the second article of this series, in which the general importance of pollination by birds in the New Zealand forest was strongly emphasized. It is necessary only to point out here that while in the untouched forest itself the greater part of the work will probably still be carried out by the tui and the bell-bird, to which the native timber-trees had become more intimately adapted before the white-eye came to New Zealand, still in settled districts where these birds are less common the ubiquitous white-eye will doubtless perform good service. Even in the city it is a common sight in winter or late - autumn to see whiteeyes busily engaged on the flowers of. the brush-wattle (Albizzia lophantha). In the bush itself the flowers of the various ratas (Metrosideros spp.) are visited for their honey, while their, relative, ? the ornamental pohutukawa of our gardens and sea-coasts, receives the same attentions. So much for the white-eye’s work in the pollination of trees and shrubs. This is a subject on which further and fuller observation is greatly needed, and it is one which can be studied by observation alone. In other parts of this investigation it is conceivable that the examination of birds’ stomachs might be of some service; in this part it would obviously be useless.

In May last almost every patch of inkweed - plants [Phytolacca octandra) in the Auckland District was the centre of an animated scene owing to the parties of white-eyes which were feeding with avidity on the berries. In early portions of the- district the bright-red bare spikes gave striking evidence of the quantity of fruit already eaten. Inkweed is dependent on birds for its spread ; the hard • black seeds could not easily be carried by any other method. It must not be supposed, however, that the white-eye is the sole exploiter of the juicy black fruit, for such introduced birds as starlings and thrushes certainly account for large quantities, while pheasants are said also to feed upon the berries. ; The blackberry —perhaps the most serious weed in New Zealandis also, so far as the seed is concerned, spread solely by birds ; but while there is little doubt that the white-eye will eat blackberries there seems no evidence to convict it of the major share in disseminating this pest. The blame for that must rather be laid at the door of certain of the introduced birds which are so overwhelmingly abundant in settled districts. The berries of another weed, the black nightshade (Solanum nigrum) ,'are also eagerly eaten by the white-eye.

In the bush itself probably none of the smaller berries are disdained. It is here that the white-eye must be considered as an ally of the forester ; so far as its forest activities are concerned, it does nothing but good.

It is when we come to the work of the white-eye in the orchard during the fruit season that there is need for all the good qualities of the species to vindicate it in the opinion of the fruit industry. - There is scarcely any fruit which is not eaten, and some, such as figs, are hardly attacked at all by i other birds. It is questionable, however, whether the greatest damage to fruit of all kinds is not the work of the blackbird, myna, starling, and thrush, which by reason of their great concentration of numbers , in settled districts, and larger size, account for a greater , quantity. There are indications that apples and pears are rarely attacked by white-eyes until the skin has first been pierced

by the stouter bills of these larger birds. The white-eye acts, as it were, as a jackal to the myna, blackbird, and starling, picking clean the cores left by them hanging or shaken to the. ground. At such times, when engaged near the ground or on a scrap-heap or in a fowlyard pecking at a bone, the white-eye falls a frequent and easy victim to the household cat. An apple which has been “ finished ” by a white-eye is always to be recognized by the frequent survival of large portions, or even almost all of the skin, surrounding the clean-picked core, but between them an empty space.

' When the white-eye turns its attention to stone-fruits it commits other damage than' the destruction of fruit alone. Mr. G. H. Cunningham in a recent bulletin (No. 101, “ Brown-rot ”) of this Department states, “ Mr. J. C. Neill informs me that at Weraroa a small bird, locally known as silver-eye (Zosterops lateralis Latham), is the cause of widespread brown-rot infection. With their beaks the birds commonly pierce infected fruits, and turn from these to healthy fruits, especially those showing colour, such as nectarines, which in turn they puncture, probably with a view of ascertaining whether they are edible.”

In discussing the work of the white-eye in destroying those multifarious insect species which are summed up in the words “ insect blights ” it is difficult to overestimate its value to all who cultivate the land. Buller wrote, “I have opened many specimens, at all seasons, and I have invariably found their stomachs crammed with minute insects and their larvae.” The cabbage or turnip aphis, which sometimes infests crops of swedes, turnips, or allied plants to an incredible extent, is frequently cleared by this winged insecticide. In accordance with the principle that birds concentrate on the most abundantly available food, the presence ’ of such a severe infestation as just described, when almost every leaf over acres is blue with aphides, is the stimulus which brings hundreds of white-eyes to the district where previously they perhaps have been but little in evidence. Here they remain until, from their viewpoint, the unexpected foodsupply is exhausted, and,, from our standpoint, until the pest is eradicated. z

Whenever a set of advantageous conditions has so far favoured an insect pest that at last it breaks all bounds, as in the case of the cabbage-aphis referred to, or whenever a pest is introduced by natural or artificial means into a district where large quantities of its food plant have been hitherto uninfested, as in the case of the blue-gum scale (Eriococcus coriaceus), there the birds will be concentrated, as vultures follow the battle. In- a large number of these cases the birds which concentrate . on the . pest are the white-eyes. With regard to the last case mentioned, that of the gum-tree scale, it must be admitted that the infestation in a new plantation is usually so overwhelming that the white-eyes are far too few to be of much service in clearing the trees. They are, however, one of the factors tending to right the balance of nature.

Another eucalypt insect eaten with avidity by the white-eye is the blue-gum psyllid (Rhinocola eucalypti) which infests the growing tips of young gums throughout the country.

The person, however, who must bear the whole cost of the whiteeye’s unfortunate proclivity for fruit is the orchardist, and it is not to be expected that he will be so altruistic as to maintain a corps of winged operators which will work solely in the interests of the farmer and the forester. Fortunately, it happens that it is in the orchard itself—the scene of its crimesthat the good points of the white-eye are displayed to the best advantage. A. H. Chisholm, writing in an Australian magazine on the relation of this bird to the orchardist, states that in Victoria it eagerly devours aphides of all species, codlinmoth, and pear-slug. A Hastings (Hawke’s Bay) orchardist has described to us how he has repeatedly watched white-eyes eating woolly aphis. It is no exaggeration to say that nearly every major insect pest of the New Zealand orchard is in one stage or another,of its existence searched out and eaten by the parties of white-eyes which subject every tree, every twig, and every crevice to the strictest surveillance. There can be no question that the value of the services rendered by the white-eye in. the orchard alone in destroying insect pests throughout the year more than counterbalance the depredations committed during the ripe-fruit season.

It has been said, that the value of insect-eating birds, of which the white-eye is one of our most conspicuous examples, is seriously lessened by the fact that ’they do not discriminate between the many beneficial insects which prey upon or parasitize our pests and the injurious insects themselves. F. E. L. Beale (1908) in the United States has answered this obj ection by showing that if birds are really indiscriminate in their taste the result will be a reduction of beneficial and injurious species by the same amount, thus leaving exactly the same proportion of useful species to attack the injurious species and maintaining the balance unaltered.