186 BIRDS OF LA PLATA 
another over the fields. It is only at the end of April, 
three months after the old birds have disappeared, 
that the young also take their departure. This is 
one of the strangest facts I have encountered in the 
migration of birds. The autumnal cold and wet 
weather seems to be the immediate cause of the 
young birds’ departure ; but in the adults, migration 
appears to be an instinct quite independent of atmos- 
pheric change. 
BLACK-AND-YELLOW CRESTED 
TYRANT 
Empidonomus aurantio-atro-cristatus 
Above cinereous; cap shortly crested, black, with a large vertical 
spot of bright yellow; wings and tail brownish black, wing-coverts 
and secondaries slightly edged with whitish; beneath as above but 
tather paler, and with a very slight yellow tinge on the crissum; 
bill and feet black; length 6.5 inches. 
ALCIDE D’ORBIGNY met with this fine species in 
Corrientes, and Dr. Burmeister in Entrerios, and 
again near Mendoza. In the neighbourhood of 
Concepcion Mr. Barrows speaks of it as a “* not very 
abundant summer resident, but one not easily over- 
looked, owing to its habit of perching on the topmost 
twig of any tree on which it alights, making forays 
from time to time, when tempted by its winged 
prey.” 7 
In the vicinity of Buenos Ayres, which may be 
