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Birds; and in Mr. Macgillivray's, the heads, at least, of nearly all the land birds are represented.

With so much already done pictorially and descriptively, on the subject of British ornithology, it may be considered superfluous to treat of the birds of Ireland in a separate work, but, in the author's opinion, every country should possess a Natural History specially appertaining to itself. In the publications referred to, the birds of Ireland have been but briefly indicated,—a species generally dismissed in a single line, and so much appearing only in two works; —those of Sir Wm. Jardine and Mr. Yarrell.

The least reflection will convince any one who appreciates the geographical distribution of species, that the birds of Ireland are in this respect even more interesting than those of Great Britain, as, within its latitude and longitude, Ireland is the "ultima Thule," the extreme western limit to which the European species not found in the Western Hemisphere, resort. The geographical position of the island, also renders it occasionally the first European land on which North American species, after having crossed the Atlantic, alight.

Considerable differences, too, consequent on physical causes, will be found to exist in the economy of the same species in Great Britain and Ireland.

The Physical Geography or natural features of the country compared with those of Great Britain, cannot be said to deprive Ireland of more than one species (the ptarmigan). The relative proportion in the two countries, of land to water, of heaths and bogs to cultivated grounds and plantations, has influence only on the number of individuals.

Nor does the difference in the mineralogical structure of Ireland compared with Great Britain affect the actual presence of any species, although it is the primary cause which influences the number of individuals prevailing in different parts of the island. The plants which appear on particular soils attract such land birds as feed upon their seeds. The submarine rocks and grounds on which sea-weeds grow plentifully so as to afford shelter to the minute fishes, and the molluscous and crustaceous animals on which the wading and swimming birds feed, tempt them in greater numbers to the neighbouring shores. The oozy, the sandy, the gravelly, the stony, the rocky beach, has each its favourite species, as has every peculiar natural or artificial feature of a country from the level of the sea to the most lofty mountain summit.

The difference in climate between Ireland and Great Britain cannot be said to deprive the former island of any species found in the latter. The comparative mildness of winter in the more western island has, however, great influence on birds. Even in the north of Ireland, a few land species, considered as birds of passage in England, except in the extreme south, become resident; and some grallatorial birds remain throughout the winter, although found only in the south of England at this season. The soft-billed birds also being generally able to procure abundance of food, are by the comparatively high temperature, more inclined to song at this period of the year. The humidity of the climate, together with the great extent of bog throughout the island, brings hither to winter, different species of grallatorial and other birds, in much greater numbers than prevail in England or Scotland. The extent of moist and rich meadows in summer has a similar, but more limited, influence. The want of extensive districts of old timber seems, when fully considered, to have little effect in excluding from Ireland species which inhabit Great Britain.

To the laws of geographical distribution alone must, I conceive, be attributed our want of species not affected by any of the foregoing causes,—viz., physical geography, mineralogical structure, climate, and absence of old timber. It should be borne in mind that in all the preceding remarks the mere absence or presence of species is considered; consequently, nothing is said of birds from different causes being less frequently met with in Ireland, than in particular parts of England or Scotland. Such points will be fully treated of under the respective species.

Although in their polar and equatorial migrations, the crossing of a sea,—as the Mediterranean * for instance,—offers no obstacle to birds, yet is it different when they are spreading latitudinally; either to the east or to the west, in which case the migration of many species terminates at the margin of the sea. Were Ireland therefore geographically joined to Great Britain, some species that are not now found would certainly inhabit it, but the junction would make no difference with respect to others:—resident as well as migratory birds. In that event, we should in the east of Ireland at least, have those species which are found throughout the most western portion of Great Britain in the same parallel of latitude; but not those whose range of distribution does not extend to the most western counties of England and to Wales. The species which Ireland would and would not have, under such circumstances, may be inferred from an examination of the summary appended to the end of each Order of Birds, where the distribution over Great Britain of the species not known as Irish, is pointed out. We should, for example, if the country suited them, have as resident birds, the green woodpecker and the nuthatch; of annual summer migrants, the wood wren and the tree pipit. But we should not have the stock dove,—a resident species in the midland and eastern counties of England;—nor would the melodious nightingale favour us with its presence, so definitively marked is the line of its migration. As to other species, which are found though rarely to the westward,—in Cornwall and Wales,—as the lesser whitethroat, &c, they might then, as a matter of course, be expected as rare visitants; such they possibly may be now, though more unfrequently than they would be in the other instance.

* A paper on birds seen crossing the Mediterranean in spring, by the author, will be fully given in the appendix to the last volume; but it was considered desirable to notice each bird included there when treating of its species. This was done that a person might be enabled on referring to any species to have the whole information respecting it before him at once. The author, however, feels that a reader of the matter continuously, may accuse him of too frequent allusion to the subject.

In like manner, the junction of Great Britain throughout its parallels of latitude, with the nearest continental land, would add greatly to the number of British birds, that island being as deficient comparatively in those of the most western European countries, as Ireland is, in comparison with it. The sea lying between the shores of Great Britain and the continent, has the same effect as that extending between the former and Ireland. Were there an island even of equal size to Ireland, situated as far distant to the westward of that country as it is from Great Britain, the diminution of species would be still greater than that actually existing between Ireland and Great Britain, and so on, in an increased ratio, were island after island, about equidistant from each other, placed still farther to the westward.

The falling off would be owing to the principle, that species continue diminishing (each within its different range) the farther we recede from their metropolis, and that the diminution is accelerated by the insular nature of the land, as opposed to its being conterminous or continental.

The preceding remarks apply only to islands like Great Britain and Ireland lying near a continent and deriving their birds thence.* t There are, however, instances of islands situated sufficiently near large continents to admit of the flight of birds from the latter, and yet deriving comparatively few, or none of their species from them. The most remarkable example is presented by the Galapagos archipelago, situated under the equatorial line, and which, though only 500 to 600 miles westward of the coast of South America, does not contain a land bird from the continent. Even some of the islands of the group have their peculiar species, J Full information on this most interesting subject will be found in Mr. Darwin's excellent journal, kept during the Surveying Voyages of H.M.S. Adventure and Beagle, vol. iii. p. 461 and 473-478. Madagascar, the nearest part of which is only about 250 miles distant from the coast of Africa and extending about 1,000 miles in a parallel direction, offers another striking instance of an island not deriving its fauna from the neighbouring continent. Of 113 known species of birds of Madagascar, 68 are peculiar to it. The fullest information on the subject of the ornithology of that island will be found in a comprehensive essay by Dr. G. Hartlaub of Bremen, published in the Annals of Natural History for Dec, 1848, p. 383-396. Por a knowledge of it, and its translation from a German journal, the English reader is indebted to Mr. H. E. Strickland.

It is interesting to observe how birds are affected by the opera

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* One species only, the red grouse, is peculiar.to the British Islands.

t These views were announced with great brevity in my Report on the Vertebrate Fauna of Ireland drawn up for the British Association for the Advancement of Science, and published in the volume for 1840. At the meeting of that Association held at Cambridge in 1845, Professor Edw. Forbes brought forward a very elaborate communication, accounting for the distribution of the species contained in the existing fauna and flora of the British Islands, on geological data. This highly interesting and remarkable essay (pp. 98) was subsequently published in the 1st volume of Memoirs of the Geological Survey of Great Britain.

J The flora of these islands is equally peculiar. See an admirable paper on this subject by Dr. Joseph D. Hooker in the Linneean Transactions, vol. xx. part 2 (1847).

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