iSSs.] Hensiiaw o?i Birds observed in Ncvj Mexico. 3^9 



gin to put in an appearance, and soon assert a place for themselves 

 in the shape of large groves. Wherever fire has devastated the pine 

 tracts the fire-cleared space is immediately occupied by aspens, 

 which spring up in the shape of extremely dense thickets — so 

 dense that in them the vision is limited to the space of a very few 

 feet. These are the favorite haunts of deer and bear. Every- 

 where the streams are densely fringed with brush of various sorts, 

 chiefly, however, willows and alders, and it is these thickets that 

 form the chief resort for the smaller birds. Flowers of many 

 kinds and of various hues are visible on all sides, and no sooner 

 is one species through flowering than another takes its place. In 

 short, the flora is of the character usually pertaining to mountain 

 areas of low latitude where a deep and fertile soil, added to a 

 copious rainfall, combine to produce an abundant vegetation. 



Our observations began sufficiently early (July 18) to make 

 sure of all the summer residents, and they were continued until the 

 close, or near the close, of the fall migration, the first indications 

 of which were noticed about August i. 



I was particularly interested in ascertaining the exact time of 

 the beginning of the fall migration, but it is a matter of no little 

 difficulty to determine, in the case of a given locality, just when 

 the first movement southward begins ; nor is it less difficult in the 

 case of a given species of bird. Among the smaller birds, the 

 first act in the final drama of migration is the assemblage of indi- 

 viduals into flocks, either of one or of many species. But this 

 gathering begins as soon as the young are fairly on the wing, and, 

 in the instance of many species, before the young are strong 

 enough to travel. It is quite certain that the small birds generally 

 do not undertake the fall journey until the old ones have some- 

 what recuperated from the effects of family cares, and until the 

 young have gained their full strength. But, so far as obser- 

 vation of these flocks goes, there is little to be learned, since it 

 is practically impossible to determine whether the flocks under 

 observation from day to day consist of the same individuals, or are 

 fresh arrivals from farther north. For instance, on our arrival, 

 July t8, many of the Nuthatches and Audubon's Warblers had 

 already gathered into flocks of old and young, and while in flocks 

 the young passed from the nestling into fall plumage, and the adults 

 donned their fall dress. There was thus an interval of probably 

 three weeks before any of them migrated, if indeed the Nut- 



