in their progress by numbers of wolves, foxes, and other predaceous quadrupeds, which attack and devour the stragglers.

The Pronged-horned Antelope, as well as the Rein-deer, appears to go northward in the summer, and return to the south in the winter.

Dr. Richardson remarks to me in a letter,"The Musk-ox and Rein-deer feed chiefly on lichens, and therefore frequent the Barren Lands and primitive rocks, which are clothed with these plants. They resort in winter, when the snow is deep, to the skirts of the woods, and feed on the lichens which hang from the trees, but on every favourable change of weather they return to the Barren Grounds. Insummer they migrate to the moist pastures on the sea-coast, and eat grass; because the lichens on the Barren Lands are then parched by the drought, and too hard to be eaten. The young grass is, I suppose, better fitted for the fawns, which are dropped about the time the deer reach the coast." In all this we see the hand of Providence directing them to those places where the necessary sustenance may be had.

The same gentleman has remarked a singular circumstance with regard to the American Black Bear. In general, this species hybernates in the northern parts of the fur countries; but it

1 Antilope furcata.

VOL. I.

2 Ursus Americanus.

H

has been observed in certain years, and very severe winters, that great numbers enter the United States from the northward. These were all lean, and generally males. The natives

assert, that a bear that is not fat cannot hybernate; therefore, those that have not acquired sufficient fat when winter overtakes them, necessarily emigrate to a milder climate.1

A migration of an animal of the equine genus was observed by Mr. Campbell in South Africa. The Quagga, a kind of wild ass, travels in bands of two or three hundred, in winter, from the tropics southward to a district, in the vicinity of the Malalaveen river, reported to be warmer than within the tropic of Capricorn, when the sun has retired to the northern hemisphere. They stay here for two or three months, which is called the Bushmen's harvest. The lions, who follow the quaggas, are the chief butchers. During this season, the first thing the bushman does, when he awakes, is to see whether he can spy any vultures hovering in the heavens at a great height; under them he is sure to find a quagga, which a lion has slaughtered in the night.

But the animals which are most noted for their migrations, from a cold to a warm climate, and vice versa, are the birds, which, as having dominion in the air, are enabled to transport them

1 Faun. Boreal-americ. i. 16.

selves with greater ease, and with the interposition of fewer obstacles, than the quadrupeds, the theatre of whose motions is the earth, intersected by rivers and mountain ridges, which renders their periodical transit less easy to accomplish. The number of birds that migrate, if we take Dr. Richardson's scale, for those of North America, as a rule, compared with those that reside the whole year in a country, is about five-sixths, a very large proportion; but as the summer residents are replaced by winter ones, the difference is less striking, and the desertion less apparent and annoying. The celebrated Dr. Jenner, in a very ingenious posthumous paper, in the Philosophical Transactions for 1824, has produced many arguments to prove that the periodical migrations of birds are the result, not of the approach of the cold or hot seasons, but of the absence or presence of a stimulus connected with the original law, "Increase and multiply." That when they feel it. they seek their summer, and when it ceases its action, their winter quarters. In one case, the animal winging its way to a climate and country best suited to the great purpose impressed upon it by its Creator, of producing and rearing a progeny; and in the other returning to a home, most congenial to its nature, and best supplying its wants.

The cause of emigration, in both cases, had

previously been attributed to the changes of the temperature gradually produced by the change of seasons, and the growing scarcity of food resulting from it. But Mr. Jenner has observed that these cannot be the causes that occasion the migration of those birds that leave us early in the year, as the cuckoo,' which disappears in the beginning of July; and the swift,* which takes its departure early in the following month. At these times they can feel no cold blast to benumb them, and the food that forms their usual support is in the greatest abundance.

There seems to be some analogy between the birds that migrate annually to warmer climates to spend their winter, and those animals, which remaining in a country, seek a subterranean, or other close retreat, to shelter them from the rigours of that season, and in which they continue in a torpid state, till spring revives them and they issue from their hiding-places to fulfil the first law of their Creator. Several instances also are upon record, even with regard to birds that usually migrate, of their having been found torpid in the clefts and cavities of trees; and Spallanzani relates experiments which prove that swallows can bear a certain degree of cold when torpid. I do not recollect any observations which serve to prove that hybernating

1 Cuculus canorus.

Cypselus apus.

animals are regulated by the temperature as to the season at which they prepare to retire for the winter, except as to insects, which, with few exceptions, are of that description. My learned coadjutor, Mr. Spence, in our Introduction to Entomology, has some remarks on this subject, which seem, at first sight, to prove that the disappearance of insects, at least those of the Coleoptera order or beetles, is not preceded by any remarkable lowering of the temperature; on the contrary, he observed a great number of various genera congregating with this view when the thermometer was fifty-eight degrees in the shade.1 This was about the middle of October. But there is one circumstance to which he has not adverted, which may tend to reconcile this fact with the received opinion. The nights, at this time of the year are often cold when the days are hot, the latter also are much shortened and the former lengthened, so that the sum-total of heat received from the sun is very much diminished, which may be the exciting cause of their hybernating at this time, when the diurnal temperature is so considerable.

With regard to the swift, these birds seem to avoid heat, they lie by in the middle of the day, and only appear in the morning and evening. Their early migration from this country may

Introd. to Ent. ii. 433.