1922] Johnson — Notes on Distribution and Habits of Bird-Flies 79 



NOTES ON DISTRIBUTION AND HABITS OF SOME OF 

 THE BIRD-FLIES, HIPPOBOSCIDvE. 



By Chakles W. Johnson, 



Boston Society of Natural History. 



The following notes on this interesting group of flies have 

 been brought together in the hope of thereby encouraging orni- 

 thologists to observe more closeh' the occurence of these insects 

 on the various species of birds. While the wide distribution and 

 great diversity of hosts frequented by one species seems some- 

 what at variance with the distribution of other insects as well as 

 their hosts, it is impossible with the limited material and data at 

 hand to arrive at any other conclusion regarding the species. 

 Highly speciahzed forms always lose man}' of the distinguishing 

 specific characters present in the species of the higher groups less 

 restricted in their habits. Living as these flies do under similar 

 and uniform conditions, notwithstanding their wide distribu- 

 tion, they would naturally show but little variation. 



The occurence of the same species of fly upon non-migrating 

 birds confined both to the tropical and boreal regions would in- 

 dicate that they are naturally transmitted from one to the other 

 by the migratory species; and the interesting example of phoresy 

 recorded below shows how the various species of the wingless 

 Mallophaga are also distributed. 



One of the peculiar habits of these flies, and one which 

 probably accounts for so few of them being taken b}^ ornithol- 

 ogists, is that thej^ are rarely seen while the bird is warm, but as 

 the dead bird becomes cold they dart from it as if terror-stricken 

 at losing their host, for if another cannot be found soon, it pro- 

 bably means death. If in this quick fhght they happen to alight 

 on one's clothes, there is a possibility of capturing them, if 

 caught firml}^ between the thumb and finger, for their smooth, 

 flattened bodies slip easily through one's fingers and when once 

 they escape they are rarely seen again, as thej^ dart into any little 

 crevice that offers protection. 



Their method of reproduction admits of no great increase, 

 producing but one large egg at a time, which develops into a 



