^°1908^^1 General Notes. 485 



Lake ami on Moses Lake, in Douglas County. Twenty or thirty seen in 

 190.5, 190(3. and again in 1908. 



Dendrocygna bicolor. Fulvous Tree-duck. — One specimen secured 

 from a flock of ten on Gray's Harbor, Oct. 3, 1905, by Willis G. Hopkins, 

 Esq., of Aberdeen, and now in his possession. It is interesting to note in. 

 this connection that a flock of eleven birds appeared at Alberni, B. C. 

 (Vancouver Id.), on the 29th of September of the same year. From this: 

 flock five were secured by Mr. J. S. Rollin, a rancher; and one of these^ 

 a handsome male, now stands in the Provincial Museum at Victoria. 



Puffinus opisthomelas. Black-vented Shearwater. — "Off Cape 

 Flattery in June." (A. W. Anthony, in epist., Jan. 15, 1907.) 



Puffinus tenuirostris. Slender-billed She.\rw.\ter. — "Off Cape 

 Flattery in October and November." (A. W. Anthony, in epist., Jan. 15, 

 1907.) In August, 1905, Mr. Bowles witnessed the migration of countless 

 thousands of these birds a quarter of a mile off-shore, at Moclips, and 

 secured specimens. 



Oceanodroma furcata. Fork-tailed Petrel. — "Just off the Cape." 

 (A. W. Anthony, as above.) 



Phaleris psittacula. Paroquet Auklet. "I have seen it between 

 Port Townseud and Cape Flattery." (A. W. Anthony, in epist., Jan. 15, 

 1907.) — W. Leon Dawson, Seattle, Washington. 



Averaging Migration Dates. — What is the best way of averaging the 

 dates of bird arrivals? This is a question that often arises in connection 

 with the migration work of the Biological Survey. 



Commenting on the method used here, Mr. Witmer Stone says (Proc 

 Acad. Nat. Sci. Phila., 1908, p. 138): "As so little has been attempted in 

 the way of combining local migration records, I find it difficult to discuss 

 the comparative value of different methods. Some casual allusions by 

 Prof. Cooke to the methods employed by him, form indeed the only con- 

 tribution to the subject with which I am familiar. He recognizes the 

 danger of including the latest dates of arrival in computing averages and 

 rejects them, just as I have advocated above, but in deciding how many 

 to reject his method seems to lack definiteness and to involve the personal 

 equation. He says (Auk, 1907, p. 347), '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.' 

 This would seem to imply an arbitrary selection of ' the probable normal ' 

 date before any averaging is done, which seems to be a dangerous method." 



For the Ijenefit of any that are interested in the subject I will give my 

 method in full and if any one can suggest a better, I am open to conviction. 



What is desired in our work, is a date that represents the average time- 

 of the arrival of the first in normal migration. The securing of such a date 

 requires the rejection of both extra early and extra late dates. The 

 principal problem is the determining of where to draw these limits. My 

 study of the relation of bird migration to the weather has convinced me 



