Chapter VIII —125— Natural Factors 



plants. He found that the birds tested might be divided into three 

 groups : 



1. Birds which crush everything, even the hardest fruits and seeds, 

 in their gizzards. When picking up seeds from the ground, they usu- 

 ally crack and discard their outer coats or shells and destroy the 

 embryos. In the droppings of these birds there was not once found a 

 single seed capable of germination. 



2. Birds which leave hard seeds uncrushed, the stones and hard 

 seeds of fleshy fruits passing uninjured through their intestines, while 

 soft seeds and fruits are destroyed. In the droppings of these birds, 

 after feeding, there were found cherry stones as large as 15 mm. in 

 diameter, all of which proved to have retained their germinating 

 power. 



J. Birds swallowing small seeds but regurgitating seeds of a diam- 

 eter of 3-5 mm. or over. A peculiarity of this group of birds is the 

 great rapidity with which seeds pass through the intestines. The seeds 

 of Samhucus nigra are evacuated by these birds after only half an hour 

 and those of Rihes petraeum after three-quarters of an hour, while 

 other seeds require not more than iK to 3 hours. As many as 75-80 

 per cent of these seeds germinate. 



On the basis of these experiments Kerner came to the conclusion 

 that hard seeds and fruits could scarcely be endozoically disseminated 

 by birds, since, as they pass through the bird's gizzard, they are usu- 

 ally ground up. Although this does not hold true in the case of the 

 seeds of fleshy fruits, here we have a different obstacle to their wide 

 dispersal, viz., the short time that they remain in the crop and in- 

 testines of the birds that devour them. Hence, Kerner concluded that 

 plants with fleshy fruits may be dispersed by the aid of birds in a 

 single year not more than for several miles and only during a long 

 period of years might gradually be so dispersed over an extensive 

 territory. 



As regards the dispersal of seeds by birds carrying them on the sur- 

 face of their bodies, Kerner considers this quite possible, but he is of 

 the opinion that the number of plants so spread is not great. They 

 embrace, for the most part, shore and swamp plants, particularly, as 

 Kerner established by personal observation, small, annual plants. 



Marloth ascribes to birds of passage the transport of seeds of 

 northern plants across the equator into South Africa. On the other 

 hand, the Danish ornithologist Winge (cited by Schroter, 1934), 

 having investigated thousands of birds of passage that had killed 

 themselves by flying into Danish lighthouses, found that without 

 exception they had empty stomachs and that not a single one had 

 seeds or fruits adhering to their feathers, beaks, or feet. Grxjnbach 

 and MosELEY ascribe to the albatross and to many species of birds 

 belonging to the genera Porcellana and Puffiniis, that make their nests 

 in dense vegetation and make annual, long, trans-oceanic flights, an 

 important role in the dissemination of seeds. Werth, on the other 

 hand, reports that on such birds, flying to Kerguelen Island, he did 

 not once find any seeds or fruits adhering to their bodies, and he con- 

 cludes that, if any had so adhered, they had been washed off in the 

 ocean when the birds alighted to rest. 



