This Tyrant is a solitary bird, though often many individuals are found within call of each other, and they sometimes even unite in a loose flock. It is found throughout the Argentine country, ranging south to the Rio Negro, in Patagonia, but abounds most on the Buenos-Ayrean pampas, where it performs a partial migration. Most of the _Tæniopteræ_ seek their food by preference on the bare level ground, or where the vegetation is most scanty. This species varies somewhat in habits, and seldom runs on the ground, and chiefly inhabits the desert plains, where the large grasses flourish. On one occasion when I was with an expedition on the pampas for several weeks, every day a number of these birds would gather and follow us; perched here and there on the tall grasses with their bosoms toward us, they often looked at a distance like large white flowers. Old gauchos have told me that fifty years ago they were abundant all over the pampas, but have disappeared wherever the giant grasses have been eaten down, and have given place to a different vegetation. Their note is a long, low whistle, the usual language of the _Tæniopteræ_; but in this species it is very like a human whistle, on account of which the bird is named _Boyero_ (ox-driver) on the pampas. One severe winter great numbers of them appeared in the neighbourhood of Buenos Ayres, and it was amusing to see the dogs thrown into a great state of excitement by the low whistling notes heard perpetually from all sides. Every few moments they would start up and stare about them to ascertain where the deceptive call came from, and in spite of many disappointments they would occasionally all rush away, loudly barking, into the plantation, convinced that some person there was whistling to call them. The Black-Crown makes a somewhat shallow nest in a bush or large clump of grass, and lays four white eggs, with large dark red spots, chiefly at the big end. I cannot refrain from quoting a passage from Mr. Barrows's paper, descriptive of the lively temper and habits of this bird:--