104 
HABIT AND STRUCTURE 
ascertained only by compiling the data of many workers, but its local 
distribution, or habitat, can be determined by a single observer. Won- 
derful as it is that the range of so mobile a creature as a bird should 
have more or less well defined boundaries, beyond which it rarely 
advances, even more remarkable is it that within the limits of this 
range the bird often should have still more sharply marked haunts. 
Thus, shore, salt and fresh marshes, meadow, upland, bush, deciduous 
or coniferous forests, all have birds which, when nesting, are restricted 
to them, and the mapping of the habitats of the birds in one’s locality 
is one of the interesting duties of the local ornithologist. The rarer 
birds will often be found confined to certain areas where perhaps a 
small colony may be established, and one should note whether it in- 
creases or decreases and attempt to learn the reasons for its success or 
failure. 
Vegetation as it influences the food-supply or offers suitable nesting 
sites, will be found to be the chief factor in controlling the distribution 
of birds locally; and it is important to record, during the course of 
years, those fluctuations in the numbers of a species due to changes 
in the character of the country incident to man’s presence as he fells 
Fig. 11. Probelike bill of Woodcock, showing extent to which upper mandible 
can be moved. (One-half natural size.) 
forests, drains marshes, permits the growth of scrub on fallow land, 
introduces new types or sources of food, furnishes new nesting-sites, 
etc. (See, especially, the Introduction to Brewster’s “Birds of the Cam- 
bridge Region.”) 
It is interesting, too, to observe the distribution of a bird during the 
day; where does it feed? where does it sleep? does it have regular fly- 
ways between feeding-ground and roost? 
Habit and Structure . — The relation between form and function is 
in most cases so obvious that even the casual observer is impressed by 
the admirable adjustment existing between a bird’s habits and its 
structure. The subject has been dealt with at length by Headley, 
Beebe and others, and offers far less opportunity for original investi- 
gation by the local student than is found, for example, in a study of 
nesting habits. Nevertheless he should learn from personal observation, 
when possible, the part that bill, wings, feet and tail play in a bird’s life. 
Uses of the Bill. — Birds’ bills usually take the form of forceps or 
probes rivaling in variety of shape the combined outfits of the sur- 
