As at Pulqué and the Pilcomayo, birds were hard pressed for nesting-sites. Giant club-cacti apparently were at a premium. The old, disused nests of brush-birds (_Synallaxis_), or _leñateros_, were inhabited by mocking-birds which built a nest of their own within the huge structure of twigs; and, when the mocking-birds were away, cowbirds slipped in and deposited a few eggs. One mocking-bird had been so unwise as to place its nest in a thorny bush covered with dense foliage so that it could not be watched from a distance and defended from cowbirds; before the owners were ready to use their new home, it had received many visits from the black parasites (_M. b. bonariensis_) who left their cards in the shape of fourteen speckled eggs. We collected this “set” but have the idea that this only encouraged the cowbirds to increased efforts. The abundance of ducks in South America in places where one least expects to find them, is a source of never-ending surprise. A small stream flows through the valley at Tilcara. It is nowhere more than twenty feet across, and two or three feet deep, but flocks of green-winged teals visited it regularly at dawn and dusk. They swam in the rapid water, and then lined up on the rocky bank for a quiet nap. The inhabitants of Tilcara shot many, but others came to the same place daily. Of mammals there were but few. Cavies, as usual, lived among the rock piles and in the stone fences, and a few other small rodents inhabited the grain-fields. One day we secured a fine specimen of the rare, elusive yellow cat called _gato pampero_, or pampas-cat. It was stealing cautiously along the river-bank; but I am unable to say whether it had come in quest of fish or merely for the purpose of quenching its thirst. Our work in this region being completed, we returned to Perico, and prepared for the journey to Embarcacion. CHAPTER XXIV THE CHACO, SUGAR-PLANTATIONS AND RICE MARSHES--A SEARCH FOR A RARE BIRD The train for the Chaco left Perico at 9 P. M. It was composed largely of second-class coaches crowded with immigrants, mostly Italians bound for various parts of the great land that is being rapidly thrown open to colonization. There was, however, also a compartment-car in which we had taken the precaution of making a reservation some time in advance. The darkness prevented our seeing the landscape through which we passed, but on our return we noted that there was little change from that around Perico as far as San Pedro. There were, however, numerous fields of sugar-cane, some of very great size. Beyond San Pedro the country is all of the Chaco type; that is, vast stretches of pampas liberally sprinkled with islands of forest. The Vermejo, a river about the size of the Wabash, was crossed on a steel bridge three miles before reaching our destination, which was at six o’clock the following morning.