GOMMENSALISM 



19 



birds might deliberately place snails in their plumage (see also p. 127 

 for a description of "anting") before starting on a long voyage in order 

 to provide themselves with at least one meal on the trip. Whether the 

 presence of these snails is accidental or not, it is certainly a method by 

 which their range can be extended — even to remote oceanic islands. 

 Even more extraordinary, and reminiscent of the ancient fable of the 

 eagle and the wren, is the record of a migrating short-eared owl trans- 

 porting a live goldcrest. 



So far we have considered only those commensal relationships in 

 which the bird plays the active role, seeking either food, protection or 

 suitable nesting sites, or perhaps all three, from an indifferent or at 

 any rate acquiescent partner. The greater number of so-called com- 

 mensal relationships involving birds, however, are those in which 

 arthropods are the active partners (see Chap. 14). Birds' nests form an 

 ideal environment for these animals and within them insects and mites 

 teem in thousands. The chief benefit which the majority of these nest- 

 dwellers enjoy is no doubt the relative dryness and warmth of the 

 habitat. They have solved a very ancient problem : "Again, if two lie 

 together, then they have heat : but how can one be warm alone ?' 



Moth, Tinea lafella, 

 a commensal from birds' nests (x 4.5) 



FFC— c 



