150 MICHIGAN SURVEY, 1908. 



telligently discuss the evolution of avian environments and to cor- 

 relate them with the evolution of birds themselves. It is quite prob- 

 able that one of the nia.in conditions which prevents a more rapid ad- 

 vance along evolutionary lines is in a large measure due to the almost 

 utter failure to analyze dynamically environmental complexes. Suc- 

 cession, studied in its broader aspects, should greatly aid in the for- 

 mulation of the laws governing the "struggle for existence," which is 

 frequently condemned for its indefinite character. 



From another point of view there are very important reasons for 

 urging extensive studies of this character at a relatively early date, 

 because the encroachments of civilization, which by the destruction of 

 the forests, the drainage of the land, irrigation, farming and grazing 

 of the grasslands, are rapidly destroying original environmental con- 

 ditions before they are studied ecologically. Much of Europe has al- 

 ready gone through this stage of demolition, and it is only to new and 

 relatively unimodifled countries that we can look for an adequate state- 

 ment of these problems and their relations in their original and pri- 

 marily evolutionary and developmental form. It is not improbable 

 that the next generation may wonder why some subjects, the investiga- 

 tion of which might have been delayed, have received detailed attention, 

 while other's equally or perhaps even more important have been almost 

 ignored and must forever remain unknown because of this neglect to 

 secure the "vanishing data." (Cf. Haddon, '03.) 



Such ecological studies may be expected to have a valuable reflex in- 

 fluence upon the naturalist himself. We may hope that the future re- 

 visor of a group of birds will consider a knowledge of the field relations 

 of. his specimens as an essential qualification, just as at the present 

 time a large series of specimens is held necessary. Fifty years ago a 

 limited series was considered no disqualification, just as to-day the 

 lack of a knowledge of their ecological relations is not so considered. 

 Perhaps our ideas of relative values must change. In this connection a 

 statement from Tristram ('94, p. 472) is to the point: — -"The closet 

 ^ystematist is very apt to overlook or take no count of habits, voice, 

 modification and other features of life which have an important bear- 

 ing on the modification of species. To take one instance, the short- 

 toed lark (Calandrella hrachydactyla) is spread over the countries bor- 

 dering on the Mediterranean; but along with it, in Andalusia alone is 

 found another species, Gal. lyaetida, of a rather darker color, and with 

 the secondaries generally somewhat shorter. Without further knowl- 

 edge than that obtained from a comparison of skins, it might be put 

 down as an accidental variety. But the field naturalist soon recog- 

 nizes it as a most distinct species. It ha^ a different voice, a differ- 

 ently shaped nest; and, while the common species breeds in the plains, 

 this one always resorts to the hills. The Spanish shepherds on the 

 spot recognize their distinctness, and have a name for each species." 



Many examples of similar character might be cited to show the 

 scientific value of a knowledge of the environmental relations of birds, 

 and a moment's reflection will show that the problem of succession in 

 only a small part of the general problem of environmental relations 

 of plants and animals. Attention has already been directed to the 

 relation which this general subject bears to evolutionary problems. 



