BIRDS. 
143 
especially the lower mandible, is also a little less strong, or high in proportion to 
its length. In the immature stage, I could perceive no difference whatever in the 
plumage of these birds. The proportional quantity of black and white in the 
primaries, given by Meyen as the essential character, varies in the different states 
of plumage. The specimens described by this author were procured from Chile.* 
The soles of the feet of my specimens were coloured, deep “ reddish orange,” 
and the bill dull “arterial blood-red” of Werner’s nomenclature. 
In the plains south of Buenos Ayres I saw some of these birds far inland, 
and I was told that they bred in the marshes. It is well known that the black- 
headed gull ( Xenia ridibundum), which we have seen comes so near the X. cirroce- 
phalum, frequents the inland marshes to breed. It appears to me a very inter- 
esting circumstance thus to find birds of two closely allied species preserving the 
same peculiarities of habits in Europe and in the wide plains of S. America. 
Near Buenos Ayres this gull as well as the L. dominicanus sometimes attends 
the slaughter-houses to pick up bits of meat. 
Rhynchops nigra. Linn. 
I saw this bird both on the East and West coast of South America, between 
latitudes 30° and 45°. It frequents either fresh or salt water. Near Maldonado 
(in May), on the borders of a lake, which had been nearly drained, and which 
in consequence swarmed with small fry, I watched many of these birds flying 
backwards and forwards for hours together, close to its surface. They kept their 
bills wide open, and with the lower mandible half buried in the water. Thus 
skimming the surface, generally in small flocks, they ploughed it in their course ; 
the water was quite smooth, and it formed a most curious spectacle, to behold a 
flock, each bird leaving its narrow wake on the mirror-like surface. In their 
flight they often twisted about with extreme rapidity, and so dexterously managed, 
that they ploughed up small fish with their projecting lower mandibles, and 
secured them with the upper half of their scissor-like bills. This fact I repeatedly 
witnessed, as, like swallows, they continued to fly backwards and forwards, close 
before me. Occasionally, when leaving the surface of the water, their flight was 
wild, irregular, and rapid ; they then also uttered loud harsh cries. When these 
birds were seen fishing, it was obvious that the length of the primary feathers 
was quite necessary in order to keep their wings dry. When thus employed, their 
forms resembled the symbol, by which many artists represent marine birds. The 
tail is much used in steering their irregular course. 
These birds are common far inland, along the course of the Rio Parana ; and 
* The naturalists in Lutke’s voyage, vol. iii. p. 2 55, seem to consider a gull, which they obtained at Con- 
cepcion, as the Larus Franklinii of North America. 
