18 The Wilson Bulletin — Xo. 98 



A COOPERATIVE BIRD CENSUS AT 

 WASHINGTON, D. C. 



BY HARRY C. OBERHOLSER. 



The importance of counting- the actual numbers of birds over 

 given areas, particularly during- the breeding season, has been 

 already amply demonstrated. Censuses of the birds present 

 during the height of the spring migration are also of consid- 

 erable value, both as a basis for comparison of the relative 

 numbers of the various species in the same year, and of the 

 same species in different years. Series of such observations 

 taken throughout the migration season would give a pretty 

 good idea of the volume of the migration ; and a series extend- 

 ing through a number of different years would show its fluc- 

 tuations, which, as we already know, are often considerable. 

 It is practically impossible for a single person to make satis- 

 factory observations of this kind, except over a very limited 

 area, and the best results are undoubtedly obtainable by the 

 cooperative work of a number of persons. 



The writer, with the assistance of fifteen other ornithologists, 

 planned a census of this kind in the vicinity of Washington, 

 D. C. As may be seen from the accompanying list, so many 

 ornithological experts have rarely been engaged on a similar 

 task at any one time. The day chosen was May 12, 1913, 

 which date in May may be considered the height of the spring 

 migration for the vicinity of Washington. Weather condi- 

 tions proved propitious, the day being bright and clear with 

 a rather chilly northeast wind. The country investigated con- 

 sisted of the region within 20 miles of the city of Washington, 

 and comprised the valleys of the Potomac and Anacostia 

 rivers, together with their tributary streams and the adjacent 

 uplands. The routes of the various parties, 13 in number, 

 were laid out so as to cover the country in all directions from 

 Washington. This section consists of the wide wooded val- 

 leys of the Potomac and the Anacostia rivers, along which 



