SOME birds that we know to have been at one time inhabitants of Scotland have entirely disappeared, as, for instance, the great bustard, not so long ago to be found on some of our great plains and commons, but now ousted by advancing population and cultivation. The sea eagle and the osprey are now practically extinct as nesting species; the first is a victim, in large measure, to the advent of Highland sheep farming; and both, in part at least, to the greed of the egg-collector and his tools.

On the other hand, we find some species increasing and advancing, at times in waves that one feels justified in terming phenomenal. It is some of these increasing species that are here considered.

These birds appear, on consideration, to fall into three separate categories. We find that certain species that have always, so far as our knowledge extends, inhabited our country have greatly increased in number and extended their bounds. Others, again, that have been known as passing visitors only, have settled, as it were, with us and become resident and breeding species; yet others, formerly quite unknown, have suddenly appeared and multiplied exceedingly. Of the first category we may take the starling as a striking example.

This bird is to-day the ubiquitous inhabitant of every part of the country ; and not of the country in the restricted sense of the term only, but of every village, town, and city as well. Yet those whose memories go back to the middle of the last century remember that the starling was then, comparatively, a rare and much-cherished bird. Nothing was more common than to see nesting-boxes hung on gables of houses or barns or on some adjacent trees, with a view to encourage them to take up their abode. Young starlings were eagerly sought after as pets, for which purpose the ease with which they can be tamed and their wonderful power of mimicry and even of articulation particularly recommend them.

At that time, when the bird was already spreading over the south of Scotland, it was still quite unknown over the greater part of the centre and north ; but to this there were very remarkable exceptions. There is unimpeachable evidence that the starling has been resident in numbers in Orkney and Shetland, in the Outer Hebrides and the extreme north of Caithness `from time immemorial'; it may be noted, in proof of its long residence, that the Highlanders have for it their own Gaelic name `Druid.'

The invasion of Scotland by the starling has been exhaustively treated by Mr. J. A. Harvie-Brown, as also in his series of volumes on The Vertebrate Fauna of Scotland. The question of the actual causes of such dispersals is a large one, and it must suffice here to say that it seems probable that, as a rule, such movements are caused by pressure arising from congestion of numbers in the older centres; so that the superfluous population is forced to overflow and to find a passage along the lines that are to them those of 'least resistance.' Thus, while the advancing wave was pushed northward from England, the Outer Islands had probably received their quota long before, from the old-established colonies in Orkney and Shetland. Whence these latter got their first visitors we are left to guess. Very possibly the original colonists followed the same route as the Norsemen, for the starling is an old-established race in Scandinavia. A widely distributed species, it is found all over Europe and Northern Africa, and extends through Russia across the Urals to Eastern Siberia and throughout India; it may therefore well be that the ancient Northern colonies were originally peopled from the North and East where the centres had become congested by advancing waves from the Further East.

The starling has great powers of mimicry, and delights in imitating the songs and call-notes of other birds. It seems especially fond of reproducing the cries of the curlew, oyster catcher, redshank and golden plover. One that some years ago had been brought up from the nest, and had learned to whistle correctly a bar or two of an air and to articulate a few words, including his own name, lived in an out-door aviary on friendly terms with the other birds, rabbits and squirrels. One day the door was inadvertently left ajar and Jacko escaped, flying to the tops of the lofty adjacent elms. When his master was summoned he was evidently enjoying the society of a chattering flock of wild starlings, and his capture seemed hopeless. Nevertheless, as soon as he heard the familiar strains of his little tune whistled to him, he left his new friends, descending in gentle spirals and lighting on his master's shoulder, and so permitted himself to be carried quietly once more to his home. Though a fearless bird as a rule, one day he got a terrible shock ; a large white pigeon, which had turned up strayed and exhausted, having been introduced into the aviary. As soon as he saw this ghostly apparition he fled shrieking into the innermost recesses of the rabbits' hutch, burying himself in the hay with piteous exclamations of `Poor Jacko ! Poor Jacko !' The unsophisticated black man is said to regard a white man, when first he sees him, as that being whom the Gael euphemistically terms 'Him whom I will not name'; and this, possibly, may be the explanation of the poor bird's terror.

The great spotted woodpecker appears to have been becoming extinct with us as a nesting species just about the time when the starling was first pushing its way into Southern Scotland, i.e. circa 1840-50. Previously it was a well-known and by no means uncommon bird in the North.' What was the cause of its virtual extinction in Scotland at that time remains a puzzle. The authority just cited seems to think that the greater care of the woodlands, involving the destruction of ancient and blasted tree-trunks, may have been a principal factor by restriction of their chief nesting and feeding localities. Be that as it may, we are to-day witnesses of the return of this species in some numbers in our southern and eastern counties. To mention localities is in such cases always unwise ; but of late years there are increasing records of this bird nesting in several Scottish counties. Now it cannot be supposed that there have been any extraordinary changes in the way of suitable surroundings and facilities to induce such an immigration ; ancient fir trees and neglected forests have not recently become more numerous. We must fall back, therefore, on the theory that these newcomers have been pushed forward by reason of over-population and congestion in old established centres.

The jackdaw is another bird that has been always with us, yet has recently increased in numbers to a remarkable extent, so much so as, in places, to constitute a nuisance. When the larger birds of prey were more numerous in the land they may have helped to keep the jackdaws within reasonable limits; but now they do not appear to have any enemies. The increase is so marked as to suggest pressure from outside sources.

A much more welcome visitor is the redstart, surely one of the most brilliant and striking of our summer migrants, and one that is certainly much more numerous than it used to be only a few decades ago. In the Fauna of Moray, Harvie-Brown describes their increasing dispersal as 'great waves,' and the writer recalls their occurrence at the altitude of 1200 feet in Spey-side. As suitable localities, such as old birchwoods, are filled up, the overplus press on in new directions. Much the same may be said of the garden warbler, doubtless also an advancing species, although one easily overlooked were it not for its striking song. The bullfinch, too, is another whose increasing numbers would be more welcome, were his attentions to the buds of fruit-trees only a little more discriminating.

The fulmar is associated in the minds of most of us with the Island of St. Kilda, where they form an important part of the food supply of the inhabitants. Of late years, however, new colonies have been found established on Handa and the mainland, and there is evidence that in the old-established nursery at St. Kilda all available nesting places are fully occupied. It seems reasonable to conclude that some, at least, of the new colonies have been peopled by the pressure from this congested centre.

Very notable has been the rapid increase and dispersal of certain ducks as resident and breeding species, e.g. the tufted duck, shoveller, pintail and pochard. The most noticeable case is, perhaps, that of the tufted duck, the increase of which is certainly very striking. Loch Leven seems to have been the first centre where it established itself, and now it is very common in suitable localities in eastern and central Scotland. Along with the ducks may be mentioned the great crested grebe, formerly a rare visitor, but of late years nesting regularly and in increasing numbers with us.

Turning now to the second category mentioned above, that of birds formerly known only as passing visitors, but of late remaining as resident and nesting species, the most remark able instance is that of the woodcock. This bird has been always, as far as we know, a regular visitor on migration, just as it still is in Germany and other parts of the continent of Europe; but to-day it is something more, being now fairly established as a breeding species all over Great

Britain. Yet, to go back to the mid-Victorian era, a woodcock's nest was then a rarity indeed, hardly to be credited without ocular demonstration. Some forty years ago I remember seeing such a nest for the first time in central Perthshire, the motionless sitting bird hardly to be distinguished from the brown leaves and bracken around it save for its prominent bead-like eyes; at the same date they were found nesting yearly in the birch-copses round a sea loch in West Argyll. Now-a-days they nest, in all likelihood, in every county in Scotland, in favourable localities in considerable and increasing numbers. When Yarrell wrote, in i843, although he mentioned as an incontrovertible fact that the woodcock did nest in Great Britain, he thought it necessary to cite particular instances in proof of it. The earliest date given by him was t832, when four nests were found in Ross-shire, where to-day nests may probably be counted by hundreds. It is interesting to note that already in 1832 the Ross-shire keepers had reported that, when disturbed, the old birds would carry away the young to safety in their claws; it is now known, however, that the young are clasped between the thighs of the parent bird, and not carried in the claws, much less under the throat, or even in the bill, as was the earlier belief.

On their first arrival on spring migration, when pairing, the woodcocks have a curious habit of issuing from covert after sunset, flying slowly with puffed-out plumage round the edges of woods and copses or down rides and open spaces, uttering from time to time two peculiar call-notes, one a harsh croak two or three times repeated, the other a sharp sibilant piping sound. It is stated, on the authority of Dr. Hoffman, that the latter note is common to both sexes, while the frog-like croak proceeds from the male alone. It is during this courting season that the German sportsmen procure their best bags, placing themselves towards evening in some open spot on a favourite route. To some of us it may seem a pity to take advantage of the poor birds' honeymoon, but it is perhaps hardly to be wondered at, seeing that in a few days all these visitors have left for their more northern breeding places. In early summer, when the woodcocks have nested with us, the same evening flights again take place in the twilight, accompanied by the peculiar notes described above. This flight follows regular lines or routes, and is termed `roding' or `robing,' a word of doubtful derivation not to be found in ordinary dictionaries. May it not simply mean `roading,' - i.e. following the accustomed roads or lines of flight?

In considering the circumstances of this remarkable change of habit in the woodcock, as regards its remaining with us as a habitual nesting species, we do not find any striking change in localities or conditions to account for its altered habit. No doubt the woodcock is singularly sensitive to climatic conditions, and a continuance of severe and adverse seasons must necessarily govern their movements to some extent; but the only satisfying explanation of so great a change seems to be that the older breeding centres had become congested.

It now remains to consider the third category-that is, the case of birds formerly quite unknown but now becoming common and increasing, and of these the stock dove is an interesting and remarkable example. Referring once more to the middle of last century, and indeed to a later date, we find that this bird was absolutely unknown in Scotland, although to be found, if somewhat sparsely, in certain localities in England. Dresser' quotes from a note in the Ibis of 1865, by Mr. A. G. More, as follows: ` The bird seems to be most numerous in some of the midland and eastern counties of England, and has not been observed in either Scotland or Ireland.' Gray mentions the stock dove merely in an 'observation,' under the heading of the ring dove, as having been recorded from Caithness and once from Orkney, and seems to have been somewhat doubtful as to its identification. The phenomenal increase of these birds up to 1883 has been recorded by Mr. J. A. Harvie-Brown and its subsequent stages in his volumes on the Vertebrate Fauna of Moray and Tay Basins. In the latter volume, p. 263, he says: `At the present time the stock dove is a more abundant species than the former-time wood pigeon-at least so it is often reported to me by observant gamekeepers in my own district of central Scotland and by others who have frequent opportunities of making observations.

The stock dove is now widely spread over all suitable areas of southern and eastern Scotland, extending well to the north-east, the wave of invasion having been in suddenness and volume quite phenomenal. It is interesting, therefore, to note that a German authority, Friderich, states that it is becoming much less common in Germany, especially in localities where population and traffic have increased. If this is correct it is somewhat remarkable; for in its extension here it does not appear to exhibit any shyness or dislike to civilisation, having multiplied exceedingly in some of our most highly cultivated and populous districts. Nor can it be said that there is any change in this country to render it more inviting to this bird as a breeding habitat, for it nests by preference in hollow trees, whence its German name `Hohl-Taube,' and there are not any increasing facilities here of that nature. Where such hollow trees are not forthcoming they nest readily in rabbit-holes or in hollows in rocks, or in thickly-tufted ivy-clumps. They take freely, too, to artificial nesting-boxes specially put up for them.

The stock dove is readily distinguished from the common wood pigeon, being of slenderer build and considerably smaller, measuring only some 13 inches in length as against 16 to 17 inches in the case of the latter. The white patch on the neck of the wood pigeon is entirely wanting, being replaced there by bright metallic green, nor is there any white on the wings. The call-note, too, is distinctly different, resembling somewhat that of the rock dove.

We have seen that in the case of the stock dove, as in that of the woodcock, there are no changes in the country, apparent to us, to account for its advent and stay; we come back, then, to the same conclusion, that we are witnessing the result of pressure from congested population, overflowing along the most natural and easy lines.

The whole subject of dispersal and distribution is full of interest and of difficulty. The mysteries of bird migration, their extraordinary journeys, the unfailing instinct that brings them yearly seeking an approach, as some believe, to their original place of origin, have a great fascination. These migrations appear to precede the settlement of new breeding stations; a process that has been going on throughout the centuries and in every department of the creation, and one of which, now and then, as in these instances, we catch a passing glimpse.