486 General Notes. [g^J^ 



that birds seldom vary on account of the season more than six days either 

 way from their average date of arrival. An example will show how this 

 limit of six days is employed. The Hooded Warbler has been reported 

 as arriving at Washington, D. C, on the following dates during fifteen 

 different years: April 19, 26, 27, 27, 29, 29, 30, May 1, 1, 3, 6, 8, 9, 10, 12. 

 The average of these fifteen dates as they stand is May 2. The first re- 

 jection drops April 19 as too early, and May 9, 10, and 12 as too late. 

 The average of the remaining dates is May 1. It is now seen that May 8, 

 should also be discarded. The average of the ten dates left is April 30. 

 This date of April 30 is considered as the "probable normal date of arrival," 

 so far as our records stand at the present time, and is publishetl as the 

 "average date of spring arrival" based on ten years' records. 



How near this date is to the truth cari be surmised from the amount of 

 variation in the records. The differences between each of the ten dates 

 used and April 30 is, in days, as follows; 4, 3, 3, 1, 1, 0, 1, 1, 3, 6 — a 

 total of 23, which divided by ten gives 2.3 days as the probable error; 

 i. e., it is probable that the date April 30 is within 2.3 days of correct. 

 The greater the number of observations and the closer these are in agree- 

 ment, the smaller will be the probable error. Thus in the case of the 

 White-eyed Vireo at Washington, D. C, the earliest dates of arrival for 

 twenty-two years are: April 18, 18, 19, 19, 20, 21, 21, 22, 22, 22, 22, 23, 

 23, 23, 24, 24, 24, 25, 25, 26, 26, 26 — average, April 23; average variation 

 from this date, 2.1 days. The most uniform record we have in all our 

 four hundred thousand notes on bird migration is that of the Chimney 

 Swift at New Market, Va. The dates of arrival are: April 10, 11, 11, 12, 

 12, 12 12, 14, 14, 14, 15, 15, 15, 16, 16, 16, 16, 16, 16. Average, April 14; 

 average variation, 1.7 days. This indicates that if the record was ex- 

 tended indefinitely, to a hundred years or more, the probability is that 

 the average date finally obtained would not vary more than 1.7 days from 

 April 14. — Wells W. Cooke, Biological Survey, Washington, D. C. 



Ontario Bird Notes. — Brunnich's Murre. A flight of Briinnich's 

 Murre Uria lomvia) appeared at Toronto on November 29, 1907, and for 

 several days dead birds were picked up on the shores of Lake Ontario. 

 They were reported in the Niagara River below the Falls and in Lake Erie 

 on December 1, and in the Detroit River on the 4th and individuals were 

 picked up at Woodstock, Strathroy, and other inland points in south- 

 western Ontario. All the birds examined had empty stomachs as has 

 been the case in all previous migrations. 



Gannet. a young Gannet (Sula bassana) was picked up dead, about 

 the last week of November, 1907, by Mr. Joseph Gilmore, on his farm in 

 the township of Wainfleet, ten miles southwest of Welland, Ont., and 

 several miles from Lake Erie. The bird was in bad condition when found 

 and had lost a leg, but it was preserved and is in the possession of Mr. 

 Gilmore. Mr. Jos. S. Wallace was the first to recognize the bird and I am 

 indebted to him for the record and photographs of the specimen. 



