DOMESTIC MARTIN 25 
difference in strength or intonation. This cir- 
cumstance appears very remarkable to me, because, 
though two species do sometimes possess a few notes 
alike, the greater part of their language is generally 
different ; also because birds of the same species in 
different localities vary more in language than in 
any other particular. This last observation, however, 
applies more to resident than to migratory species. 
I am inclined to believe that the Purple and 
Domestic Martins form one dimorphic species, like 
the Carrion and Hooded Crows of Europe, and that, 
like these two Crows, they would inter-breed should 
their nesting areas overlap. 
DOMESTIC MARTIN 
Progne chalybea 
Upper parts deep purple-blue;  wing- and tail-feathers black, 
glossed with steel-blue ; throat and chest ash-colour ; breast, abdomen, 
and under tail-coverts pure white; length 8 inches. Female similar. 
Tuis species, distinguished from the Purple Martin 
by its white underparts, ranges from Mexico to 
Buenos Ayres, the extreme limit of its range being 
about 250 miles south of that city. It was well called 
Golondrina domestica by Azara, being pre-eminently 
domestic in its habits. It never breeds in banks as 
the Purple Martin often does, or in the domed nests 
of other birds in trees, a situation always resorted to 
by the Tree Martin, and occasionally by the Common 
