REACTIONS ON LAND 73 



fied by Swedish investigators in particular (cf. v. Post, 1862; Lomas, 

 1905; Naumann, 1922; Lundquist, 1927). 



A number of general studies have been made of the excreta of 

 animals in terms of accumulation and their gross relation to the soil, 

 such as the guano deposits of Laysan Island where approximately a 

 million birds nest in two square miles of territory (Dill and Bryant, 

 1911). Errington (1930) has made a considerable study of the pellet 

 contents of raptors, which accumulate in some degree about nests and 

 in rookeries, while Kellogg (cf. Stoddard, 1931:209) has analyzed more 

 than a thousand regurgitated pellets of the marsh hawk from a ''roost" 

 in Florida. Dearborn (1932) has described the diversified nature of 

 mammal droppings, through which materials of slow decomposition, 

 such as hair, feathers, and bones, are also added to the soil mass. 



This contribution of animal matter, a large part of which is avail- 

 able more or less readily, has for the most part been ignored by stu- 

 dents of soil fertility, probably because their attention has been 

 focused on field soils where animal life is much reduced. Recently, 

 Greene and Reynard (1932) have made a quantitative examination 

 of this question on a grazing range, with especial reference to the 

 kangaroo rat and the wood rat (Fig. 15). Both these rodents defecate 

 more or less throughout their tunnels, thus leading to an increase in 

 soluble salts, particularly the bicarbonates and nitrates of calcium 

 and magnesium, as well as chlorides from urine. The carbon dioxide 

 of respiration was thought to be the probable cause of the increase of 

 calcium bicarbonate, as a result of the conversion of carbonate, and 

 it was also suggested that this gas increases the availability of phos- 

 phorus in the soil. The most outstanding effect was that upon soluble 

 nitrates, which rose from a probable maximum of 15 parts per million 

 for desert soils to 221 and 570 parts per million in two different bur- 

 rows, making a total of 3.65 and 10.26 pounds, respectively. 



The contribution to the soil by animal chitinous bodies and cal- 

 careous and bony skeletons, though small by comparison with that of 

 plants, is still a matter of significance. This is a field in which quanti- 

 tative determinations are practically unknown, and the annual turn- 

 over as a whole or for any particular group must be left to conjecture 

 at present. The question is also complicated by the coactions of scav- 

 engers and sapronts of all sorts, as a consequence of which the return 

 is indirect or delayed. The effect of any particular species is chiefly 

 a resultant of size and number, and hence it is possible that inverte- 

 brates may often play a larger part than birds or mammals. The 

 approximate number of invertebrates per square meter at the time of 

 the midsummer maximum has been estimated at 3,300 by McAfee 



