28 The Ornithology of Chester County 



Philadelphia, may prove interesting in comparison 

 with the valuable combination averages by Dr. Stone 

 for the Delaware Valley Ornithological Club. 



I have been at some disadvantage in working 

 alone, especially when unable to make frequent visits 

 to the habitats of extremely local species, but on 

 the other hand the percentage of error may possibly 

 be less than where several observers of less experi- 

 ence work a neighborhood. My experience in horizon 

 and census work has taught me something of com- 

 parative abundance and I believe my averages for 

 bulk arrival and departure to be of greater value and 

 more nearly correct than the averages of first arrival 

 and last seen ; especially taking in consideration the 

 utter impossibility of always distinguishing the bona 

 fide first arrival from the occasional holdover. 



Migration at Berwyn is seldom as well marked as 

 in many other sections of the county; especially the 

 vernal flight, when many of the smaller local land 

 birds appear tardily via the Darby creek, and others 

 pass in a northeasterly direction. The visible au- 

 tumnal movement is more direct and attended with 

 greater numbers; the usual route southwesterly, the 

 day fliers : Killdeer, Dove, Hawks, Blue Jay, Grack- 

 les, Blackbirds, Swallows and Robin; the Canada 

 Goose and Nighthawk, by day or night, and the 

 Sandpiper by night. It is only occasional that a 

 great movement is detected in the nightfliers, like 

 that of September 24th, 1916, when the sky was 

 partly overcast, the clouds thin and low, with mod- 

 erate west wind ; the air appeared alive with whis- 

 pering voices of the small migrants at no great 

 height, from dusk to late at night. 



