DIRECTIONS FOE MEASUREMENT. 55 



species of the genus. We have a reference to several standard authors, 

 which may be consulted if desired. Turning back a few pages, we find that 

 the genus Plcus belongs to the sub-family Picince, of the family Picidce, of 

 the order Scansores; and each of these groups is defined, illustrated, or 

 otherwise noticed. In this way, it is believed, a single specimen may 

 be made the means of imparting no inconsiderable amount of information. 



2. HOAV TO MEASURE A SPECIMEN. 



§ 95. For large birds, a tape line showing inches and fourths will do : 

 for small ones, a foot rule, graduated for inches and eighths, or Ijctter, deci- 

 mals to hundredths, must be used ; and tor all nice measurements the divid- 

 ers are indispensable. 



§ 96. In comparing measurements made with those given in the Synop- 

 sis, absolute agreement must not ho expected ; individual specimens vary 

 too much for this. It will geuerally he satisfactory enough, if the discrep- 

 ancy is not beyond certain bounds. A variation of, say, five per cent., may 

 be safely allowed on birds not larger than a robin : from this size up to that 

 of a crow or hawk, ten per cent. ; for larger birds even more. Some birds 

 vary up to twenty or twenty-five per cent., in their total length at least. 

 So if I say of a sparrow for instance, "length five inches," and the speci- 

 men is found to be anywhere between four and three-fourths and five and 

 one-fourth, it will be quite near enough. Put: — the relative proportions 

 of the different parts of a bird are much more constant, and here less dis- 

 crepancy is allowable. Thus "tarsus longer than the middle toe," or the re- 

 verse, is often a matter of much less than a quarter of an inch : and as it is 

 upon just such nice points as this that a great many of the generic analyses 

 rest, the necessity of the utmost accuracy in measuring, for use of the key, 

 becomes obvious. When I find it necessary to use the qualification "about" 

 (as, "bill about==tsiVsus") I proljabl}' never mean to indicate a difference of 

 more than five per cent, of the length of the part in question. 



§ 97. "Length." Distance between the tip of the bill and the end of the 

 longest tail feather. Lay the bird on its back on the ruler on a table, take 

 hold of the bill with one hand, and of both legs with the other; pull with 

 reasonable force, to get the curve all out of the neck ; hold the bird thus 

 with tip of the bill flush with the end of the rule, and see how much the end 

 of the tail points to. Put the tape line in place of the ruler, in the same 

 way, for larger birds. 



§ 98. "Extent." Distance between the tips of the outspread wings. 

 They must be fulhj outstretched. With the bird on its back, crosswise on 

 the ruler, its bill pointing to your breast, take hold of right and left meta- 

 carpus with thumb and forefinger of your right and left hand, respectively, 

 stretch with reasonable force, getting one wing-tip flush with one end of the 

 ruler, and see how much the other wing-tip points to. With large birds, 

 pull away as hard as you please, and use the taljle, floor, or side of the 

 room, as convenient; mark the points and apply tape line. 



