The Woodheiver Family. 253 



life; and the only reasonable explanation of this 

 habit in birds — one which is not very common in 

 the 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 Anumbius, 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 



