82 Barrows on Birds of the Lotver Uruguay. [April 



America, has a smaller northern race in Central America. P. 

 hefatica of Mexico has, according to Mr. Ridgway, a smaller 

 southern race in Paraguay. In reference to this latter case, and 

 to Geothlypis poliocephala, decrease in size southward south of 

 the equator is equivalent of course to decrease in size northward 

 north of the equator. 



The instances of decrease in size southward in North American 

 Oscines above-noticed — and they embrace all the marked ones 

 that I now recall — seem to be explainable under and illustrations 

 of the first proposition above cited. In general. North American 

 birds belong either to northern or cosmopolitan types, with a few 

 pertaining to distinctively tropical American groups which are 

 represented with us by a few outlying members ; and it is among 

 these that we note the exceptional increase in size southward. 



Geographical variation in size in birds has been hitherto discussed 

 chiefly in reference to those of North America, but that the law 

 of decrease in size southward also holds for the birds of Europe 

 and Asia is indicated beyond question, but not at present perhaps 

 equally demonstrable. That south of the equator there is, as 

 there should be on general principles, an increase in size southward 

 among conspecific forms is also susceptible of illustration, but it 

 is beyond the province of this note to enter upon the subject 

 here. Later there may be occasion to take up the matter in 

 detail. 



BIRDS OF THE LOWER URUGUAY. 



BY WALTER B. BARROWS. 



It was in the early days of July, 1879, that the writer entered 

 the waters of La Plata and through the chilly mists which were 

 driven before a stiff' "pampero" beheld the great flocks of Gulls 

 and Terns which, during the winter months, make these waters 

 their home. Two months later he was set down in the darkness 

 of early morning on the muddy shore of the west bank of the Rio 

 Uruguay, about 200 miles north of Buenos Aires, at the old town 

 of Concepcion del Uruguay. In the immediate vicinity of this 



