THE OSPREY. 



49 



The first plan proposed is that of taking ddily horizons : 

 the second is in brief the taking of the bird census 

 in given localities. 



A season's work as outlined in the above could 

 scarcely fail of being an invaluable aid to the study 

 of geographical distribution. Such arbitrary terms 

 as 'abundant,' 'common,' ' tolerably common,' 'not 

 uncommon,' 'not common,' 'not rare,' 'rare,' etc., 

 are relative only, absolutely unreliable, and often mis- 

 leading. 



For three consecutive seasons I have paid particu- 

 lar attention to the numbering of the breeding War- 

 blers within a short distance of my home, finally 

 drawing a rough, though approximately correct, scale 

 map of a section one square mile in area, of which 

 my home is the center, on which I have noted the 

 breeding grounds and number of individuals of each 

 species. It is in short a census of the Warbler popu- 

 lation as far as known to me, reasonably correct, and 

 are under rather than over estimates of the true 

 number of avian inhabitants. 



A brief description of this tract of land will suffice: 

 The south hills of the great Chester Valley running 

 through the center from southwest to northeast from 

 the watershed between the Schuylkill — four miles to 

 the northwest — and the Delaware — fifteen miles to 

 the southeast ; — virtually the backbone of this square 

 tract of land, corrugated by numerous ravines. On 

 the north, piercing deeply into the hills, begin the 

 diminutive tributaries of Trout Run ; and on the 

 south those of the Darby Creek. On the southern 

 slope nestles the village of Berwyn. 



Of the 640 acres less than 240 acres are at all suit- 

 able for the habitation of the various members of this 

 family. This includes a large percentage of timber, 

 principally young chestnut and oak, with a scattering 

 of hickory, poplar, beech, maple, walnut, etc. ; three 

 small, swampy thickets, a few neglected pastures, 

 and numerous brambly fence rows. It contains fully 

 one thousand human inhabitants, situated principally 

 on the southern half and which includes almost the 

 entire village. Viewing it from whatever standpoint, 

 it contains no advantages over a like area in almost 

 any part of the country. 



The Black and White Warbler loves the steep 

 wooded hillsides, above the noisy little brooks, tuck- 

 ing its nest under a drift of dead leaves mid the laurel 

 or huckleberry bushes. So secretive is its nature in 

 nesting time, unless stumbled upon when with young 

 or recognized by its weak song, that it is only of late 

 years that it has been admitted as a summer resident 

 in the lists of our county, and despite the number of 

 experienced working ornithologists, it is even yet con- 

 sidered as rare. I have noted eight pairs and could 

 more than double this number in several tracts of no 

 greater extent but a short distance away. If Chester 

 County averages only sixteen to the square mile, and 

 I see no reason why it should not, at the close of the 

 nesting season of 1897, counting the normal increase 



in young it must have contained 38,000 individuals. 

 So much for our 'rather rare breeder' and guardian 

 of the bark of the forest trees. 



The Worm-eating Warbler differs but little from 

 the Black and White in its choice of habitation, but 

 however the overflow occasionally build on the level, 

 a trait probably not unknown to the latter also. 

 Although I collected for ten years before I found this 

 species breeding, this is no indication of its rarity. It 

 is probably more abundant in many other portions 

 of the county, particularly the Brandywine Creek 

 region. I have records of seventeen pairs in this 

 tract for this season alone. Allowing for the propor- 

 tion of cleared land, which is 88 per cent. {Pfnnsyl- 

 Tania /•'orcstry Report, 'gj), it would not be an over- 

 estimation to place the number for this year, includ- 

 ing the increase, at 77,000. 



The Blue-winged Warbler is a rather common 

 rare' breeder and more evenly distributed than either 

 of the foregoing species. It inhabits both upland and 

 swampy thickets, brambly fence rows and neglected 

 pastures, although liable to be overlooked in many 

 places owing to its unobtrusiveness. 



It is equally common in the adjacent counties of 

 Delaware, Montgomery and Berks. Their combined 

 areas with Chester ought to produce the total of 

 170,000 at the close of the season, if my count of 

 twelve pairs and their increase is a fair criterion. 



Ignoring the Ovenbird, Yellow-breasted Chat, and 

 Maryland Yellow-throat of which I can offer no reli- 

 able estimate, owing to the great abundance of the 

 first, the extreme variability of the second and on ac- 

 count of the few and small swamps, the poor repre- 

 sentation (twelve pairs) of the last. 



I found the Kentucky Warbler in great abundance, 

 their clear whistle ringing out here and there along 

 the edges of the thickets and woods. They love the 

 open woods and partly cleared thickets, dwelling 

 midst the rank ferns, poison ivy, mandrake, skunk 

 cabbage, low creeping dogwood, and numberless other 

 wood plants. But for their attachment for a com- 

 paratively narrow territory of which their nests are 

 the center, a census would be an utter impossibility. 

 With a record of 42 pairs I have strong grounds for 

 suspecting that I have missed a number. It is most 

 numerous in York, Chester, Delaware and Southern 

 Montgomery counties; /. e., speaking for Eastern 

 Pennsylvania only. Allowing for the normal increase 

 which I will place at four young to the pair, the four 

 counties produce the enormous number of 590,000. 

 The number of vegetation-destroying insects and 

 larvae this great army annually destroy is incalculable. 



Placing a conservative estimate upon the number 

 of individuals of the above seven species and adding 

 a modest count for the Summer Yellowbird, which is 

 common in some parts of the county, and the rare 

 Louisiana Water Thrush, the total number subsist- 

 ing within the borders of Chester County for a period 



