It is difficult, for me at least, to understand how we should now have in the United States so many birds which, not more than twenty years ago, were nowhere to be found in our country. Of these new-comers the Olive-sided Flycatcher is one, and one, too, whose size and song render it very conspicuous among its kindred. That birds should thus suddenly make their appearance, and at once diffuse themselves over almost the whole of the country, is indeed a very curious fact; and were similar changes to take place in the other tribes of animals, and in other countries, the arrangements of systematic writers would have to undergo corresponding revolutions, a circumstance which would tend to add to the confusion arising from the continual shiftings, combinations disseverings, abrasions of names, and alterations of method, which the interpreters of nature are pleased to dignify with the name of science.

The discovery of this species is due to my amiable and learned friend NUTTALL, part of whose account of its habits I have pleasure in laying before you. When, a few years ago, I rambled, as I do now, in quest of knowledge, scarcely an individual could be found in the United States conversant with birds. At the present day there are many, with whom I am personally acquainted, besides others, who have fully proved their zeal and activity by their discoveries and descriptions.

On the 8th of August, 1832, while walking out from Boston towards the country seat of the Honourable THOMAS H. PERKINS, along with my friend NUTTALL, we were suddenly saluted with the note of this bird. As I had never seen it, I leaped over the fence beside us, and cautiously approached the tree on which a male was perched and singing. Desiring my friend to go in search of a gun, I watched the motions of the devoted bird. He returned with a large musket, a cow's horn filled with powder, and a handful of shot nearly as large as peas; but, just as I commenced charging this curious piece, I discovered that it was flintless! We were nearly a mile distant from Mr. PERKINS' house, but as we were resolved to have the bird, we proceeded to it with all despatch, procured a gun, and returning to the tree, found the Flycatcher, examined its flight and manners for awhile, and at length shot it. As the representative of a species, I made a drawing of this individual, which you will find copied in the plate indicated above. But now let us attend to NUTTALL'S account.

"This undescribed species, which appertains to the group of Pewees, was obtained in the woods of Mount Auburn, in this vicinity, by Mr. JOHN BETHUNE, of Cambridge, on the 7th of June, 1830. This and the second specimen acquired soon afterwards, were females on the point of incubation. A third individual of the same sex was killed on the 21st of June, 1831. They were all of them fat, and had their stomach filled with torn fragments of wild bees, wasps, and other similar insects. I have watched the motions of two other living individuals, who appeared tyrannical and quarrelsome, even with each other. The attack was always accompanied with a whining querulous twitter. Their dispute was apparently, like that of savages, about the rights of their respective hunting-grounds. One of the birds, the female, whom I usually saw alone, was uncommonly sedentary. The territory she seemed determined to claim was circumscribed by the tops of a cluster of Virginian junipers or red cedars, and an adjoining elm and decayed cherry-tree. From this sovereign station, in the solitude of a barren and sandy piece of forest, adjoining Mount Auburn, she kept a sharp look-out for passing insects, and pursued them with great vigour and success as soon as they appeared, sometimes chasing them to the ground, and generally resuming her perch with an additional mouthful, which she swallowed at leisure. On ascending to her station, she occasionally quivered her wings and tail, erected her blowzy cap, and kept up a whistling, oft-repeated, whining call of pu, pu, then varied to pu, pip, and pip, pu, also at times pip, pip, pu, pip, pip pip, pu, pu, pip, or tu, tu, tu, and sometimes tu, tu. This shrill, pensive, and quick whistle, sometimes dropped almost to a whisper, or merely pu. The tone is, in fact, much like that of the phu, phu, phu, of the Fish Hawk. The male, however, besides this note, at long intervals had a call of eh phebee, or h'phebea, almost exactly in the tone of the circular tin whistle or bird call, being loud, shrill, and guttural at the commencement. The nest of this pair I at length discovered in the horizontal branch of a tall red cedar, forty or fifty feet from the ground. It was formed much in the manner of the King-bird's, externally made of interlaced dead twigs of the cedar, internally of wiry stolons of the common cinquefoil, dry grass, and some fragments of branching lichen or usnea. It contained three young, and had probably four eggs. The eggs had been hatched about the 20th of June, so that the pair had arrived in this vicinity about the close of May. The young remained in the nest no less than twenty-three days, and were fed from the first on beetles and perfect insects, which appeared to have been wholly digested, without any regurgitation. Towards the close of this protracted period, the young could fly with all the celerity of their parents, and they probably went to and from the nest before abandoning it. The male was at this time extremely watchful, and frequently followed me from his usual residence, after my paying him a visit, nearly half a mile. These birds, which I watched on several successive days, were no way timid, and allowed me for some time previous to visiting their nest, to investigate them and the premises they had chosen, without showing any sign of alarm or particular observation."

I received from my friend the following additional account, in a letter dated September 12, 1833. "Something serious has happened to our pair of the new Flycatchers (Muscicapa Cooperi), which have for three years at least, bred and passed the summer in the grounds of Mount Auburn. This summer they were no longer seen. It is true they were not very well used last year; for, in the first place, I took two of the four eggs they had laid, when they deserted the nest, and soon, within little more than a stone's-throw, they renewed their labours, and made a second, which was also visited; but from this I believe they raised a small brood. The nest, as before, was placed on a horizontal branch of a red cedar, and made chiefly of the smallest interlaced twigs collected from the dead limbs of the same tree, in all cases so thin, like that of the Tanager, as to let the light readily through its interstices. An egg you have, which, as to size, so completely resembles that of the Wood Pewee, as to make one and the same description serve for both; that is to say, a yellowish cream-white, with spots of reddish-brown, of a light and dark shade. All the nests, three in number, were within 150 yards of each other respectively. I saw another pair once in a small piece of dry pine wood in Mount Auburn one year; but they did not stay long. A third pair I saw the summer before the last, on the edge of the marsh towards West Cambridge Pond; these appeared resident. The next pair I had the rare good fortune to see in your company, by which means they have been masterly fi, red. It is beyond a doubt M. borealis of RICHARDSON, but I believe Mr. COOPER and myself discovered it previously, at least before, the appearance of Dr. RICHARDSON's Northern Zoology."

In the course of my journey farther eastward, I found this species here and there in Massachusetts and the state of Maine, as far as Mars Hill, and subsequently on the Magdeleine Islands, and the coast of Labrador; but I have not yet been able to discover its line of migration, or the time of its arrival in the Southern States.

This species has never been observed in South Carolina, although I met with it in Georgia, as well as in the Texas, in the month of April. According to Mr. NUTTALL, it is "a common inhabitant of the dark fir woods of the Columbia, where they arrive towards the close of May. We again heard," he continues, "at intervals, the same curious call, like 'gh-phebea, and sometimes like the guttural sound of p h p-phebee, commencing with a sort of suppressed chuck; at other times the notes varied into a lively and sometimes quick p t-petoway. This no doubt is the note which WILSON attributed to the Wood Pewee. When approached, as usual, or when calling, we heard the pu pu pu." A single specimen was shot on the banks of the Saskatchewan, and has been described in the Fauna Boreali-Americana under the name of Tyrannus borealis.

Dr. BREWER has sent me the following note:--"A female specimen obtained by me measures 6 1/2 inches in length, being fully half an inch shorter than the male. Nape of the neck, belly, vent, throat, and flanks white; in the latter, continued to the back, so as to be visible above the fold of the wings; a broad olive band across the breast; in all other respects it resembles the male. A nest, which I have examined, measures five inches in external diameter, and three and a half inches in internal, and is about half an inch deep. It is composed entirely of roots and fibres of moss. It is, moreover, very rudely constructed, and is almost wholly flat, resembling the nest of no other Flycatcher I have seen, but having some similitude to that of the Cuckoo."

OLIVE-SIDED FLYCATCHER Or PE-PE, Muscicapa Cooperi, Nutt. Man., vol. i. p. 282.

TYRANNUS BOREALIS, NORTHERN TYRANT, Swains. and Rich. F. Bor. Amer., vol. ii. p. 141.

OLIVE-SIDED FLYCATCHER, Muscicapa Cooperi, Aud. Orn. Biog., vol. ii. p. 422; vol. v. p. 422.

Wing pointed, second quill longest, first longer than third; tail emarginate, the three first primaries very slightly attenuated at the ends; upper parts, cheeks, and sides of the neck, dusky brown, tinged with greyish-olive, the head darker; quills and tail blackish-brown, the secondaries margined with brownish-white; downy feathers on the sides of the rump white; lower parts greyish-white, the sides dusky grey. Young similar to adult.

Male, 7 1/2, 12 3/4.

From Texas northward along the Atlantic. Never seen far in the interior. Columbia river. Migratory. THE BALSAM OR SILVER FIR.

PINUS BALSAMEA, Willd., Sp. Pl., vol. iv. p. 504. Pursch, Fl. Amer. Sept., vol. ii. p. 639.--ABIES BALSAMIFERA, Mich., Fl. Amer., vol. ii. p. 207. --MONOECIA MONADELPHIA, Linn.--CONIFERAE, Juss.

This beautiful fir is abundant in the State of Maine, where I made a drawing of the twig before you. It grows on elevated rocky ground, often near streams or rivers. Its general form is conical, the lower branches coming off horizontally near the ground, and the succeeding ones becoming gradually more oblique, until the uppermost are nearly erect. The leaves and cones become so resinous in autumn, that, in climbing one of these trees, a person is besmeared with the excreted juice, which is then white, transparent, and almost fluid. The leaves are solitary, flat, emarginate, or entire, bright green above, and glaucous or silvery beneath; the cones cylindrical, erect, with short obovate, serrulate, mucronate scales. It is abundant in the British provinces, the Northern States, and in the higher parts of the Alleghany Mountains. The height does not exceed fifty feet. The bark is smooth, the wood light and resinous. The resin is collected and sold under the names of Balm of Gilead and Canada Balsam.