SYMBIOSIS 27 



relationship is near bee-hives in gardens. Birds which normally nest 

 around human habitations are gregarious and as we have already 

 noted, several species of birds and families of birds which manifest 

 general gregarious tendencies, seek protection from bees and other 

 social insects. 



There are a few British records of birds nesting and rearing young 

 in close proximity to Hymenoptera. 



(i) A jackdaw nesting two years running in a hollow tree with wild 

 bees — both birds and insects using the same entrance hole. 



(2) A jackdaw nesting in a hollow ash tree with hornets — using the 



same cavity but different entrance holes. 



(3) A swallow and wasps nesting under the same eave, with the nests 

 touching each other. 



(4) A sparrow and hornets nesting under a thatched roof situated about 

 one foot apart. 



(5) A wren and wasps nesting within six inches of each other in an 

 attic. 



All five birds reared their young successfully, which, in two instances, 

 were known to be second broods. These particular associations may 

 well have been accidental and due to a predilection for the same type 

 of nesting site. But this fact in no way detracts from the interest of such 

 records. Chance must play a very considerable part in first bringing 

 symbiotic or commensal partners together. Once such a partnership 

 between species has been firmly established, it is on the whole, fairly 

 obvious, although in the case of birds, recognition by naturalists in the 

 literature, came suprisingly late. On the other hand, in the early 

 stages before the relationship has become fixed as a specific habit, 

 individual cases are generally dismissed as coincidences. It is however, 

 unwise to disregard such isolated observations or dismiss them lightly. 

 Nothing is really known about the origins and evolution of nesting 

 associations between birds and aggressive insects or other species of 

 birds. Some workers believe it is merely a question of identical habitat 

 preference, or that the main element involved is the sociability of 

 birds. Others again consider that nesting sites close to an aggres- 

 sive species are less disturbed by predators and are therefore more 

 attractive to the birds. It is quite possible that all these factors play 

 a part and may wholly explain some of the cases concerned. Never- 



