Length to end of tail 13 3/4, to end of wings 14 1/2, to end of claws 17 3/4; extent of wings 25 1/2. Weight 6 1/2 oz.
Both sexes become darker on the upper parts, at the approach of spring. This dark colour disappears after their autumnal moult.
The tongue is 1 2/12 inch in length, slender, sagittate and papillate at the base, triangular, tapering to a fine point. On the roof of the mouth are two rows of large blunt papillæ directed backwards; the edges of the mandibles are thick and grooved; the posterior aperture of the nares linear, 9/12 long. The œsophagus, 6 3/4 inches in length, passes along the right side of the neck, and has a diameter of 3/12 of an inch in its upper part, but is dilated to 5/12 before it enters the thorax. The proventriculus is oblong, 8/12 in length, its glandules oblong. The stomach is oblong, 1 2/12 inch in length, 8/12 in breadth, its lateral muscles of moderate size, the tendons 5/12 in diameter, the cuticular lining hard, with large longitudinal rugæ, and of a deep red colour. The intestine 2 feet 8 inches long, varying in diameter from 2 1/2/12 to 2/12. The rectum 1 9/12 inch long; the cæca 4 inches 5/12 long, of an oblong form, with the extremity rounded, their diameter 1 1/2/12.
In another individual, the œsophagus is 6 1/2 inches long; the stomach 1 9/12; the intestine 2 feet 3 inches; the rectum 1 9/12, the cæca 4 1/12, their diameter 1 1/2/12.
The trachea, 4 8/12 inches long, 2 1/2/12 in diameter above, 2/12 below; of 120 unossified rings; its contractor muscles feeble, the sterno-tracheal moderate; a single pair of inferior laryngeal; the bronchial rings about 15.
COMMON TERN.
Sterna Hirundo, Linn.
PLATE CCCIX. Adult.
Although the Prince of Musignano has thought that the bird named the Common Tern in America, differs from that bearing the same name in Europe, and has in consequence changed its appellation to that of Wilson’s Tern, I am of opinion that no difference exists between the Common Terns of the two Continents. The cry of both is besides precisely similar, so that with me there is no doubt whatever as to their identity. Experience has shewn me that the markings or white spots on the primary quills of Gulls, at one time assumed as a criterion by which species might be distinguished, cannot in the least be depended on, varying, as they always do, in individuals of the same species, at almost each successive moult. Then why, Reader, should not Terns exhibit analogous changes? The fact is, they do so; and it is almost impossible, on closely inspecting a dozen or more specimens procured at the same period, in either country, to find two individuals exactly corresponding in every particular. Some have the bill almost entirely black, while others have it more or less red and black, and tipped with yellow. The length of the tail-feathers, that of the tarsus, and the size of the inter-digital membranes, are all found to differ in some degree, if minutely compared. If species are to be founded on such slight differences, an ample field is open to those who are ambitious of being discoverers. At all events, I cannot help remarking here, that it seems to me improper to impose new names on objects, until it is proved by undeniable facts that they present permanent differences.
I have observed this species along the Atlantic coast of North America, from Galveston Island in Texas to the Straits of Belle Isle on the coast of Labrador, both in spring and in early autumn. But when on the islands in Galveston Bay, in the month of April, I saw only a few arriving there from the west; whereas, in the beginning of May great numbers arrived there from the east, settled at once, and commenced breeding. I felt convinced that the numbers which came from the direction of the Floridas were much greater than those which arrived from the westward, and judged it probable that vast numbers had at the same time left the Peninsula on their way northward. Should other travellers observe the same or similar phenomena at the season mentioned, it will be proved that this species does not extend its autumnal migration so far as several others, which I observed arriving at Galveston Island from the south-west, for example, the Least Tern, Sterna minuta, the Cayenne Tern, St. cayana, and the Black Tern, St. nigra.
The Common Tern commences breeding on the coast of our Middle Districts about the 5th of May. On my voyage to Labrador, I found its eggs on the islands in the Gulf of St Lawrence, and especially on the Magdalene Islands, which I visited on the 11th of that month. On the 18th I saw them in great abundance in the neighbourhood of American Harbour, on the coast of Labrador, where thousands of Terns were plunging headlong after shrimps all round us. In that country, their eggs were deposited among the short grass, and the places which they occupied were but slightly scratched; whereas on the Magdalene Islands, where they breed on sandy ridges, slight hollows were scooped out, as is generally the case along the eastern coast of the United States. Their sojourn in Labrador is of short duration; and when we were at Newfoundland, on the 14th of August, multitudes were already passing southward. At the same period considerable numbers pass by an inland route from the Canadas, and all our great lakes, travelling along the Ohio and Mississippi. While residing at Henderson, and afterwards at Cincinnati, I had ample opportunities of watching their movements in the month of September. And yet, you will think it strange, that, during their vernal migration, I never saw one ascend any of these rivers or the streams connected with them. Perhaps the inferior temperature of the waters, compared with those of the ocean, in the early spring months, may induce them to abandon their route at that season. In autumn, on the contrary, when these rivers are heated and reduced in size, the Terns may find in them an abundant supply of the fry of various fishes. It would thus appear, being corroborated by other observations which I have made relative to migration, that species whose range is extensive, are determined in their movements by a genial temperature and an abundant supply of food.