VOl i907 IV ] General Notes. 347 



from day to day, and I also received the notes collected by the various 

 members of the Biological Survey and the National Museum in their 

 excursions around the city. Many of the notes were duplicates or of no 

 value, but after all these had been eliminated it was found that usable 

 records had been received from twenty-three persons. The question 

 then is how much additional did the twenty-three pairs of eyes observe 

 that had not been noted by me. The following is a condensed answer. 

 Seen by others and not by me 4 species 



Seen by me and not reported by others 3 



Seen by others before I saw them 44 



Seen by me before reported by others 25 



Seen by both on the same day 7 



Total 83 species 



The comparison applies only to the migrant land birds, as the facilities 

 for observing water birds in the district are too limited to make the records 

 of any value. 



When using migration records for the calculation of average dates of 

 arrival, I usually discard dates that are more than six days later than the 

 probable normal date of arrival. When this test is applied to the notes 

 the following results are obtained 



Seen by others within six days of normal, but not by me 12 species 



Seen by me within six days of normal but not reported by 



others 11 



Seen by both within six days of normal 46 



Reported by no one within six days of normal 14 



Total, 83 species 



This last item of fourteen species not recorded within six days of normal 

 is probably higher than would be obtained during most years. The month 

 of April, 1907, in Washington was the coldest for thirty-five years, and 

 many species were retarded in their movements. As the record stands 

 in this unfavorable season I obtained usable notes on 71 per cent, of the 

 species seen, while by adding the notes of the other observers, this is raised 

 to 84 per cent. Of the 79 species seen by me, 57 were noted within six 

 days of the normal time of arrival, which number is raised to G9 species 

 on the addition of the remainder of the records. 



The most interesting part of the investigation is the question of how 

 much earlier twenty-four pairs of eyes can see birds than one pair. In 

 spite of all my efforts, the larger amount of time spent in the field and the 

 great variety of country covered, more than half the species were reported 

 to me by others before I had noted their arrival. 



Yet I saw them soon afterward and the 25 species that I saw first are a 

 partial offset. The net result is that the combined notes average 1.3 days 

 earlier than my notes alone. Hence, judging by the results of this single 



