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 denned 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- 



