The W oodhewer Family, 
253 
life ; and the only reasonable explanation of this 
habit in birds — one which is not very common in 
tbe mammalia — is that such species possess the 
social temper or feeling, and live in pairs only 
because they cannot afford to live in flocks. Strictly 
gregarious species pair only for the breeding season. 
In the creepers the attachment between the birds 
thus mated for life is very great, and, as Azara 
truly says of Anumbins, so fond of each other’s 
society are these birds, that when one incubates the 
other sits at the entrance to the nest, and when one 
carries food to its young the other accompanies it, 
even if it has found nothing to carry. In these 
species that live in pairs, when the two birds are 
separated they are perpetually calling to each other, 
showing how impatient of solitude they are ; while 
even from the more solitary kind, a high-pitched 
call-note is constantly heard in the woods, for these 
birds, debarred from associating together, satisfy 
their instinct by conversing with one another over 
long distances. 
The foregoing remarks apply to the Dendrocolap- 
tidse throughout the temperate countries of South 
America — the birds inhabiting extensive grassy 
plains and marshes, and districts with a scanty or 
scattered tree and bush vegetation. In the forest 
areas of the hotter regions it is different ; there the 
birds form large gatherings or wandering bands,” 
composed of all the different species found in each 
district, associated with birds of other families — 
wood-peckers, tyrant-birds, bush shrikes, and many 
others. These miscellaneous gatherings are not of 
rare occurrence, but out of the breeding season are 
