162 BIRDS OF LA PLATA 
a 
are to be found in one or other of the various groups 
comprising the Tyrannide. 
These birds have no migration, but pair for life, 
and always remain on the same spot, and will con- 
tinue to breed in the same hole for many years, even 
where they are frequently deprived of their eggs. 
Azara saw them sometimes uniting in small flocks in 
Paraguay ; in Buenos Ayres they are always seen in 
pairs, or, after the young have left the nest, in 
families. They prefer to live near a human habitation, 
where there are trees: even one tree, in which they 
can breed and find shelter at night, will be sufficient 
to attach them to a dwelling, so great is their par- 
tiality for the clean-trodden ground where they can 
freely run about and catch insects. They haunt the 
cattle-pens, and become extremely familiar with 
the cows, horses, and sheep, following them to the 
pasture-grounds, where they are often seen perched 
on the back of a horse or other domestic animal, 
or stationed close to its nose on the ground, watching 
for insects. On the bare ground they run about with 
wonderful swiftness, and are able to overtake and 
capture flying insects without rising. The male and 
female invariably hunt together, and at intervals fly 
to some favourite perch to indulge in a duet composed 
of loud, rapid, shrill notes, somewhat metallic in 
sound. Though able to fly swiftly when in pursuit 
of a passing Hawk or other bird, at other times their 
flight is strangely slow; the round body, short blunt 
wings and tail giving the bird a somewhat curious 
appearance as it progresses laboriously through the 
