674 



SCIENCE 



[Vol. LVI, No, 1459 



stretches of the San Joaquin Valley twenty- 

 five yeare a,g0', which, were then merely arid 

 plains. The vegetation consisted of xerophi- 

 lous grasses and herbs, with here and there 

 tracts of lupine or atriplex bushes. The birds 

 observed were scattering horned larks, fewer 

 meadowlarks, and occasional burrowing owls; 

 it being winter, there were more numerous 

 Savannah sparrows and, in rain-dampened 

 places, pipits. Knowing what I do now about 

 censuses, I doubt if there were then more than 

 one bird to the acre, on an average, probably 

 much less than that ratio. 



Now, regarding the same territory, it would 

 be hard to exaggerate the amount of change in 

 vegetation which has resulted from the water- 

 ing of the ground. Orchards, alfalfa fields, 

 green pastures and streams of running water 

 lined with willows, completely occupy the land. 

 Instead of a very uniform type of environ- 

 ment, with only a few niehes and correspond- 

 ingly few species of birds, one finds, upon 

 analysis, a great variety of niches and a much 

 increased number of bird species. What is 

 more, the numbers of individuals are vastly 

 larger. To be snre, the horned lai-ks and bui-- 

 rowing owls are gone. But the meadowlarks 

 have multiplied; and, in addition, one sees 

 great numbers of Brewer blackbirds, of mock- 

 ingbirds, goldfinches, swallows, phcebes and 

 killdeers. I esitmate the mean population over 

 large areas of the San Joaquin in April, when 

 the lowest ebb for the year is reached, at 10 

 per acre, or over 6,000 per square mile. Here, 

 obviously, the conditions for abundant avian 

 population have been markedly improved by 

 the coming of the white man with his methods 

 of cultivation. 



Even more spectacular has been the faunal 

 change wrought by irrigation in Imperial 

 Valley, where luxuriant vegetation with result- 

 ing abundance of bird life has replaced the 

 original sparse vegetation of the desert which 

 supported relatively little animal life. 



Another biotic modification is brought about 

 by deforestation. Close stands of coniferous 

 trees are replaced by "slashes," by open young 

 growths, or by mixed brvish land and trees. 

 Dense forests, it is well known, are sadly lack- 



ing in bird population. The removal of the 

 forests has meant, of course, the disappearance 

 of a few, specialized avian tenants. But in 

 their place, occupying the clearings and mixed 

 growths, is a much greater population both as 

 to individuals and species. Kinglets, pUeated 

 woodpeckers, and hermit thrushes may have 

 disappeared; but fox sparrows, chipping spar- • 

 ix)ws, spotted towhees and a host of other birds 

 of like habitat preferences have come in. Cer- 

 tain little niches have been done away with; 

 but the change in the nature of the territory 

 at the hand of the lumbeiinan has resulted in 

 there being many more, new niches; each of 

 these, evidently, of gi'eater amplitude, of great- 

 er supporting power. 



Very definite change in the other direction 

 has been that made as a result of the di-aining 

 of swamp lands. Many species thereby have 

 been eliminated, locally, many more species 

 than occupy the reclaimed land; and, further- 

 more, I feel sure that the numbers of indi- 

 viduals, too, have been reduced, though not 

 in so large proportion. As instances, I would 

 refer to Nigger Slough and Gospel Swamp in 

 southern California, and to the region at the 

 confluence of the Sacramento and San Joaquin 

 Rivers in west-central California. A swamp is 

 really a very complicated type of environment ; 

 within it usually may be recognized many 

 "niches" and a correspondingly large number 

 of avian occupants. Among these are the 

 heix)ns, rails, gallinules, song sparrows, j^ellow- 

 throats and tule wrens, and, if there be open 

 water, coots, terns and several species of ducks. 

 The most serious adverse effect of the human 

 occupancy of California upon bird-life thus 

 far has, I believe, resulted from this reclama- 

 tion of the swamp lands. But, if you vrill re- 

 sort to memory, or examine a topographic map, 

 you will observe that the total area here in- 

 volved is very small compared with the terri- 

 tory that has been affected oppositely, by irri- 

 gation. Irrigated territory, moreover, is sub- 

 ject to continual and much farther spread, 

 while the possibilities of drainage are almost 

 exhausted. 



Other modifications of primitive conditions 

 as a result of the white man's occupation of 



