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nightly songster, although much more rarely so than the Nightingale.

It should be noted, too, that in almost every species, the male is peculiarly distinguished from the female, so that those, conversant with the subject, readily know the one from the other. The males of many of the tribe have more gaudy and vivid colours on their plumage; the male is also very often larger than the female. This may be strikingly seen in the Common Cock and Hen, the Turkey, and the Pheasant.

In the rapacious tribes, on the contrary, the female is generally larger than the male. WILSON informs us that the female of the Strix Virginianus, or GREAT HORNED OWL, is four inches longer than the male; and in some of the Falcon genus the difference is more considerable than this.

Sometimes, however, these distinguishing marks are by no means so apparent. The COCK BLACKBIRD is known chiefly by his intensely yellow bill, and the superior black jet of his plumage. The distinction between the Hen and Cock THRUSH is not very strongly marked; and that of the Cock and Hen PINTADO, or GUINEA FOWL, is so slight, that nothing but close observation will ascertain it. This last bird is a native of Africa, and although domesticated in this country, it rarely, if ever, acquires the habits and do cility of the Domestic Fowl. The female, if left to herself, invariably seeks some place for her nest distant and apart from the rest of the poultry; and, what is very remarkable, she deposits her eggs on the bare ground. This bird does not conform itself in its habits to climate like some others; hence, in England, it is a very bad protector of its own offspring.

The pairing of birds is also a subject which deserves attention in their Natural History. While some are mono

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ON THE PAIRING AND INCUBATION OF BIRDS. 59

gamous, and of course pair, others are polygamous, and never, unless compelled, confine themselves to individual association.

All the rapacious tribes belong to the monogamous class; the same may be said of the Perchers; the Pigeon tribe are also generally monogamous; so also appear to be all the struthious class; but the aquatic birds and waders vary in this respect; some are monogamous; others polygamous. The gallinaceous tribe are generally polygamous. Although the puerile notion that birds pair on Valentine's day in this country is not, of course, entitled to the slightest credit, yet there is no question, however, that about that period, or sooner or later in the spring, many birds cease their gregarious association, and meet only in pairs for the performance of the important office of incubation and rearing their young. Whether this association in pairs continue for more than one season by the same birds does not appear to be yet accurately ascertained. The Cuckoo is also said to be a polygamist; but we do not yet know sufficient of the babits of this bird.

There is one other fact relative to the change in the plumage of birds which may be mentioned here, namely, that sometimes the female assumes the feathers and appearance of the male bird; this has been noticed in the Common Hen, the Pea-hen, and a few others; and as this change has been most commonly observed in old birds, it has been attributed to age alone; but some late observations tend to prove that the change arises from some disease of the genital organs in female birds: for some young female birds have also been observed with male feathers; and dissections in all prove the diseased state of those organs.

Although the PERIODS of the INCUBATION of BIRDS are generally pretty regular, they are by no means exactly so,

considerable variations having been observed in them wherr opportunities have been taken, or have occurred, for such notice.

from

DUCKS have sat from GEESE from twenty-nine .

It appears that, when TURKIES have sat on the eggs of the Hen, the duration has been from seventeen to twenty. seven days; the same bird on its own eggs from twentysix to twenty-nine days. HENS sat on Ducks' eggs twenty-six to thirty-four days; on their own eggs from nineteen to twenty-four days. twenty-eight to thirty-two days. to thirty-three days. PIGEONS from seventeen to twenty days. It is extremely probable that extended observation will shew still greater irregularities in the various periods of the Incubation of Birds, which seem to increase in duration in proportion to the size of the bird: while the Ostrich and Swan require six weeks, and the solitary Dodo, it is said, seven, to complete the process, the Humming-bird takes only about twelve days.

There can be little doubt that an equability of warmth is one of the essentials in the due process of incubation. Where the Hen frequently leaves her nest and the eggs exposed, or where the nest itself is in an unsheltered situation, the process is very often retarded, sometimes, indeed, rendered wholly unproductive. Young mothers are generally worse managers of their eggs and their young than those who have had more experience; in this not differing from the human subject!

Although the number of eggs which both domestic and wild birds lay before they are diposed to sit upon them, provided they are not disturbed, is generally pretty regular, yet that number may be considerably increased by removing the eggs as they are laid, leaving one or more in the nest. In domestic fowls this has been so well ascertained, that a

Hen will lay one every day for many weeks provided one only be left in the nest, although, if left to herself, she usually sits upon about fifteen. And RAY* informs us, on the authority of Dr. LISTER, that a Swallow, whose usual number is about five, having the eggs subtracted in a similar way, laid nineteen successively and then gave over.

Young birds, when hatched, are of two kinds: one has down upon the body, the eyes open, and will pick up its food almost immediately on leaving the shell; such are the young of many or most of the aquatic tribes, and those of the Hen, Pheasant, Partridge, &c.; the mother by quaking or clucking calling the young's attention to its food the nests of such birds are usually on the ground. The other kinds (those for the most part whose nests are built on some elevation) are completely naked and the eyes closed; these require to be fed by the parent bird for two, or sometimes more, weeks. The eagerness with which these all rear up their heads and open their mouths, upon the least disturbance of the nest, is truly astonishing. They however soon become covered with feathers; from one to two weeks are, in general, a sufficient time to render them full fledged and able to fly. During this period they are, of course, often covered by the parent bird. The first kind are hived by the mother, for some time, very often during the day, and, of course, during the night; and afterwards, at longer intervals, for two, three, and sometimes more weeks, according to the more or less genial warmth of the season.

It may be mentioned too that many of the useful or harmless tribe of birds have often two, sometimes more, broods in a season; and that their eggs are commonly more or less numerous-the Hens, the Ducks, the Partridges, &c. are peculiarly so; while the eggs of the more rapacious

* Wisdom of God manifested in the works of Creation. 8vo. 1719, page 119.

tribes are generally few, and hence the increase of such birds is considerably more restricted.

Dr. Prout found the specific gravity of new laid eggs to vary from 1080 to 1090; that eggs on being kept some time became specifically lighter than water, owing to the substitution of air for a portion of the water which escapes; that an egg exposed for two years, to ordinary circumstances, lost nearly two-thirds of its weight; that an egg loses about onesixth of its weight during incubation; a quantity amounting to eight times as much as it loses under ordinary circumstances. Although, in the size and colours of eggs of the same species, there is a general conformity, yet differences occasionally occur; in some of the titmouse and tail tribe, whose eggs are usually variegated with spots, they have been seen perfectly white.

There is a very simple, yet I believe not very generally known, method of ascertaining the vitality of an egg. If, on applying the tongue to the larger end of it, warmth be felt, the egg may be presumed alive and good; if cold, the contrary, dead and bad.*

It should be also observed, that although the eggs of birds vary considerably in taste, and some are much more palatable and agreeable than others, yet none of them appears to be absolutely unwholesome as food.

In closing this short account of the incubation of birds, a singular fact must be adverted to which was first brought into public notice by Mr. YARREL, a gentleman to whom the public, as well as myself, are highly indebted for the

* On my boiling in water, for a few minutes, the egg of a Guinea Hen, ( Numida Meleagris,) which had been kept for the long period of six or seven years, the egg exploded with a report similar to that of a loud pistol: occasioned, no doubt, by the expansion of gaseous matter, arising from the decomposition of the contents of the egg.

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