FAUNA OF THE ALEUTIAN ISLANDS AND ALASKA PENINSULA 25 



mountain slope where we would find a colony of auklets nesting 

 among rock crevices. We came to the tentative conclusion that 

 vegetation grew more luxuriantly on the site of such bird colonies 

 as a result of fertilization by bird guano and waste food. This 

 vegetation was not necessarily of the same species as those grow- 

 ing on the Aleut village sites ; however, the reasons for its pres- 

 ence in the two instances may have been related. 



We did not have opportunity to study in detail the recovery of 

 vegetation on islands recently covered by volcanic ash, as Griggs 

 (1936) has done at Katmai and at Kodiak. However, little flat 

 Ogliuga Island would furnish such an opportunity. In 1930, 

 there was an eruption on Gareloi, and the ash from the erup- 

 tion covered Ogliuga. At the time of our visits in 1936 and 1937, 

 vegetation was just beginning to recover. Tall vigorous clumps 

 of coarse sedges, Carex, and some Juncus, had pushed up through 

 the ash here and there. These clumps had caught some of the 

 drifting ash driven by the wind, had pushed up higher to clear 

 the ash, and in turn had caught more wind-driven ash, until 

 mounds had been created which were similar to sand dunes. 



In the north are found the so-called bird mounds, whose origin 

 has caused much speculation. One theory is that birds such as 

 gulls and jaegers, repeatedly alighting on a small prominence, 

 fertilize the spot, thus causing exuberant vegetative growth — a 

 process that continues until a tall mound is formed. 



On nearby Kavalga Island, I found that a part of the area 

 nearest to Ogliuga evidently also had been in the path of an ash 

 fall from a volcanic eruption, probably not so heavy a fall as that 

 which covered Ogliuga. 



Some typical "bird mounds" on Kavalga were carefully dis- 

 sected, with the result shown in the accompanying diagram. In 

 figure 23, parts a and b, two such mounds show (by dark spots) 

 the wearing away, or undercutting, by wind erosion. Also, note 

 the wind erosion on the side in the diagrammatic section of an- 

 other mound, as shown in part c. 



Part c shows, in cross section, the layers of materials in one 

 of these bird mounds. Note that the first layer under the vegeta- 

 tion consists of lava sand, or ash. Beneath the first layer are the 

 alternating layers, in increasing width toward the center, of black 

 soil and rotted moss. This was, of course, a fairly crude field 

 examination, with no opportunity for more precise analysis of 

 materials. But the drifting volcanic ash on nearby Ogliuga, pil- 

 ing up in mounds around the pioneering clumps of vegetation, 

 suggested a process that may also have operated on Kavalga 



