672 



SCIENCE 



[Vol. LVI, No. 1459 



past seventy-five years; as examples, tJie trum- 

 peter swan and the whooping crane. But, com- 

 pensating for these losses, there have become 

 newly established within our territory during 

 that same period some species of foreign 

 source; as examples, ring-necked pheasant and 

 English sparrow. Cheeking up the species of 

 both categories, we can reach but the one con- 

 elusion that, as yet, so far as concerns the state 

 as a whole, there has been no real reduction in 

 the total nmnber of species; our known avi- 

 fauna at the present moment totals 582 species 

 and subspecies ; I am aware of no good ground 

 for supposing that it was one unit more or 

 less, seventy-five years ago. 



If, however, we narrow our attention to given 

 restricted localities, we are confronted with 

 evidence of real and great reduction in species, 

 up to even forty per cent, of the original num- 

 ber, I figure, in some places. It is this local 

 reduction in species, most apparent naturally 

 in eentere of human population, that has im- 

 pressed so strongly the ardent advocates of the 

 various sorts of bird protective measures. 



An entirely different phenomenon, as already 

 intimated, is comprised in the fluctuation of 

 aggregate populations, irrespective of the 

 various species, few or many, represented in 

 them. On this point, my impressions are 

 strong itihat, thi-oughout the country at lai-ge, 

 wherever human influence has had any marked 

 effect, there has been increase in the bird life. 

 In some localities, as pointed out below, this 

 increase may reach as much as tenfold. 



My reader will at once demand something 

 more tangible than "impres-sions." And I am 

 compelled regretfully to admit that aetna! 

 figures seem to be wanting. We have no ' 

 record of censuses taken fifty years ago, or 

 even twenty-five years ago. This is unfor- 

 tunate ; and it is to be hoped that further lapse 

 of time will see an improvement in this situa- 

 tion. Numerical censuses, on either an areal 

 basis or a unit-of-time basds, are now being 

 talien and recorded. The stoident of the future, 

 let us hope, will have plenty of statistical data 

 upon which to base final conclusions. 



It seems, then, that, in this discussion, I 

 must fall back upon less tangible classes of 



evidence — upon memory and upon inferences 

 from other categories of facts. Before citing 

 this evidence, however, let me introduce some 

 theoretical considerations. 



It is a recognized, established principle that 

 the presence in a region of any given bird 

 species is absolutely dependent upon, first, 

 proper food supply, second, the right kind of 

 breeding places, and third, appropriate cover 

 or protection for individuals — each of these 

 conditions as bound up with the inherent struc- 

 tural features of the bird under consideration. 

 Mark that there are three of these factors, each 

 and all of them essential; if any one of them 

 in a given region becomes effaced, the bird in 

 question can no longer exist there. There are, 

 of course, other factors essential to avian ex- 

 istence, but they affect all the birds of a given 

 fauna alike. We can deplore, wring our hands, 

 and suffer agonies of regret, but to no avail^ — • 

 except as active steps be taken to restore the 

 critical condition. As a matter of cold circum- 

 stance, a bird's disappearance in a given local- 

 ity may be irretrievable — as happens where 

 man has densely settled a territory and inci- 

 dentally or pui-posely destroyed certain of its 

 natural features unnecessary or inimical to his 

 own existence ithere. Chop down all the trees 

 and there can be no more woodpeckers; drain 

 the lakes, ponds and swamps and there can 'be 

 no more ^vater birds; remove the chaparral, 

 and wren-tits, bush-tits and thrashers can no 

 longer find proper food and shelter. Cement 

 up all the holes in the campus oaks and there 

 will be no more plain titmouses — for the reason 

 that roosting and 'brooding places essential to 

 their existence are no longer to be found. 



Each bird species native in a given region 

 has a different and very special combination of 

 requirements. Existence of each is really de- 

 termined by a very slender thi-ead of circum- 

 stances which can, in most species, be broken 

 readily. Differences must, of course, be recog- 

 nized in the degree of hardihood, or of via- 

 bility, in the various species of birds — ^some 

 are on the ragged edge of extinction, this con- 

 dition in part due to inhei-ent reduction in spe- 

 cific vigor — ^the race is naturally playing out, 

 we say; others are hardy, with a large reserve 



