OF EASTERN PENNSYLVANIA. 7 



binding of materials together, which open places 

 would seem to require ; consequently, the mud or 

 clay which ordinarily constitutes the rim of a typi- 

 cal nest and serves to join the inner and outer 

 fabrics more intimately together, is entirely dis- 

 pensed with. By an intelligent selection of locality 

 the birds have saved considerable time and labor, 

 and- also have constructed their nest none the 

 less tastefully and symmetrically. 



Many nests of the Robin frequently betray un- 

 mistakable resemblances to those of a closely allied 

 species, the mustelinus of Gmelin. These latter 

 are undoubtedly the unskilled labor of young 

 birds and adults that have never risen to eminence 

 in the art of nest-building. Many of these nests 

 might be taken as fair samples of the workman- 

 ship of the Wood Thrush. In this interpretation 

 of facts, we should expect to meet with some evi- 

 dence that migratorius is a higher type of avis 

 than mustelinus. It is well known that the young 

 of the former, or the Robin, has the breast spotted 

 precisely like the latter, or Wood Thrush in its 

 adult plumage ; but this condition of plumage is 

 of short duration and gradually merges into the 

 uniform tints of the mature bird. 



With this light upon the subject, we are pre- 

 pared to understand why resemblances should 

 obtain between certain nests of the Robin and the 

 typical ones of the Wood Thrush. Among birds, 

 as among the human species, there exist individ- 

 uals of lazy 'and careless habits; and others, dull 



