°'igi6 ] HussEY, Spring Birds of La Plata. 395 



nested in considerable numbers under the roofs of several of the observatory 

 buildings. 



This swallow is the first bird heard in the early morning in La Plata, 

 long before there is a suggestion of light in the east. 



54. Progne chalybea domestica (VieilL). — This sweet-voiced 

 Martin is met with occasionallj- in the city of La Plata as well as on its 

 outskirts, but is not common as a town bird. It has apparently suffered 

 much from the introduction of the European House Sparrow, and seems 

 now rather to avoid localities where those birds are numerous. The follow- 

 ing story, told me by a friend, shows that sometimes the Martins turn upon 

 the Sparrows. 



Dm'ing the summer of 1913-14 a pair of these Martins were seen building 

 a nest under the eaves of a building near La Plata. They had made good 

 progress, when a pair of Sparrows were noticed about the nest quite fre- 

 quently. Finally, when the nest was almost done, the Sparrows began to 

 approach the nest more closely while the owners were absent, and then to 

 clamber over it, and finally to enter it. Once, when the Martins retm-ned 

 to find the Sparrows inside, a battle followed in which the Martins were 

 decidedly worsted; after this the SpaiTows boldly took possession. Then 

 the Martins waited until both Sparrows were inside; one bird saw to it that 

 they did not escape, while the other went for mud and plastered up the 

 opening. 



55. Phaeoprogne tapera (Linn.). — This Martin is much more often 

 seen than the preceding, despite the fact that it does not gather in flocks, 

 as do the other swallows of the region. The flight of this bird has a peculiar 

 featm-e: at times the wings are depressed much as those of a duck taking 

 to water, and are constantly agitated with tremulous flutterings. This 

 bird breeds only, as far as I could learn, in the abandoned nests of the Oven- 

 bird; or, if none are available, it drives out the owners and takes possession 

 of the oven by force. 



56. Petrochelidon pyrrhonota (VieilL). — I saw this swallow only 

 on a few dates in October, and judged that it was a migrant; later I was 

 told that this is the case. 



57. Troglodytes sp. — There are two forms of Troglodytes musculus 

 found at La Plata. T . m. guarixa and T. m. hornensis. The first of 

 these is the more common; but the difference between them is so slight 

 that to most people they are a single bird. 



The Wren is very common and one of the best known birds in La Plata, 

 where it is called the " Ratonera." The song is suggestive of that of the 

 North American House Wren {T. aedon), but is shorter and less varied. 

 The nesting habits are about the same; but one remarkable case came to 

 my notice, which I shall describe here. 



About the middle of October a pair of Wrens started to build a nest under 

 a hood in the observatory grounds which had been designed as a shelter 

 for an electric light. They soon abandoned this site, built their nest else- 

 where, and raised a brood of seven. Meanwhile a pair of " Mistos " 



