186 BRITISH BIRDS. [vol. vm. 



that in time we may arrive at the causes of such 

 increase or decrease ; we may study the comparative 

 numbers of different birds in various locahties — ^how 

 many Warblers of each kind there are nesting in a 

 wood, or in a larger, more arbitrarily chosen piece of 

 country, including woods, fields, moors, lanes, and 

 ponds ; or, again, from the point of view of the environ- 

 ment rather than from that of the bird, we may take 

 a census of some region, either of a particular wood or 

 moor, or of some varied region, showing the numbers of 

 every species nesting in it. The most useful results 

 will probably be obtained from observations restricted to 

 a piece of country of one type, in fact to a geological 

 or topographical unit ; and if a wider stretch of country 

 is taken it is most desirable to note the extent and 

 character of the woods, hedges, fields and meadows, and 

 any other country included. It is not enough to know 

 that a wood of ten acres contains a certain number of, 

 say, Chiffchaffs, Willow- Wrens, and Wood- Wrens ; for 

 the proportion of these birds in woods of high forest 

 trees, beech or larch or pine, in woods of oak and hazel, 

 in woods of birch with open heathery glades, will be 

 completely different ; the birds to be found along the 

 course of an open weed-covered stream flowing between 

 flat green meadows will be very different from those found 

 by a stream flowing between banks and overhung by 

 dense bushes or by alders. Even such a small point 

 as the cutting of hedges — are they closely chpped or 

 do they grow unattended and loosely wander into the 

 lanes and fields ? — ought to be noticed. 



It is not necessary to restrict such inquiry to the 

 breeding-season ; when birds are nesting it is, of 

 course, much easier to compute their numbers, but in 

 open country, and to some extent in woods, one may 

 make very exact notes at any season ; we may, for 

 example, note the comparative number of each species 

 of Finch in the flocks on the stubble or in other places 

 during the winter ; we may observe how many days 



