212 BIRDS OF Tp PLATA 
thing for two species so closely allied to be found 
inhabiting the same district. In both birds the 
colours are arranged in precisely the same way; but 
the chestnut tint on S$. albescens is not nearly so 
deep, the browns and greys are paler, and there is 
less black on the throat. 
I am pretty sure that in Buenos Ayres it is 
migratory, and as soon as it appears in spring it 
announces its arrival by its harsh, persistent, two- 
syllabled call, wonderfully strong for so small a bird, 
and which it repeats at intervals of two or three 
seconds for half an hour without intermission. When 
close at hand it is quite as distressing as the grating 
song of a Cicada, This painful noise is uttered while 
the bird sits concealed amid the foliage of a tree, 
and is renewed at frequent intervals, and continues 
every day until the Spine-tail finds a mate, when all 
at once it becomes silent. The nest is placed in a 
low thorn-bush, sometimes only two or three feet 
above the ground, and is an oblong structure of 
sticks, twelve or fourteen inches in depth, with the 
entrance near the top, and reached by a tubular 
passage made of slender sticks, and six or seven 
inches long. From the top of the nest a crooked 
passage leads to the cavity near the bottom; this 
is lined with a little fine grass, and nine eggs are 
laid, pear-shaped and pale bluish-white in colour. 
I have found several nests with nine eggs, and there- 
fore set that down as the full number of the clutch, 
though I confess it seems very surprising that this 
bird should lay so many. When the nest is ap- 
