36 PROCEEDINGS OF THE 



years. Some conclusions however seem obvious and are of 

 considerable interest. 



Comparisons of the Foiir Local Sections. — As explained above it 

 is reasonable to suppose that the first individuals of a species 

 are likely to reach such closely situated stations as Bryn Mawr, 

 Haverford, Ardmore and West Park on the same day, even 

 though through force of circumstances the observers at these 

 stations were not all able to record the bird on that day, conse- 

 quently by taking the earliest date recorded at any one of these 

 stations we will probably have the date of the appearance of 

 that bird within the circle bounding these localities. For in- 

 stance we have the Catbird reported from these four stations on 

 April 24, April 30, April 27 and May 1. The Bryn INIawr date 

 April 24, being the earliest, is no doubt the first appearance of 

 the species in this section, while the other dates indicate either 

 the fact that the observers at these stations were unable to make 

 a thorough search for birds on the 24th, or that the earliest flight 

 of Catbirds did not visit the limited area covered by their 

 observations. If we now examine the dates for the Catbird in 

 the section including Tinicum, Swarthmore, Lansdowne and 

 Mt. Moriah, we find the dates to be April 26, April 23, April 26, 

 May 2; the earliest date for the section being the Swarthmore 

 one April 23; a very close coincidence with the date for the sec- 

 tion just north, which we have shown to be April 24. 



Considering now the dates of arrival of the Brown Thrasher, 

 we have within the Philadelphia district records from twelve 

 stations as follows: April 22 (2), April 23, April 24 (4), April 

 25, April 26 (2), April 27 and May 1, a diversity of ten days; 

 combining these into the four sections we have Moorestown sec- 

 tion, April 22; Swarthmore section, April 22; Ardmore section, 

 April 23; Olney section, April 24; a diversity of only two days, 

 from which we may infer that the first Thrashers reached the 

 Philadelphia district on April 22, appearing at points in the 

 low grounds along the Delaware from Swarthmore to Moores- 

 town, and the next day or the day following reached the higher 

 ground north of the city and the headwaters of Cobb's and 

 Darby creeks. 



Comparing now the arrivals of twenty-six species which are 



