1SS7.] Trotter o?i the Genus Helminthopkila. ^OQ 



Hybridism under nature is a further expression of decay, the 

 result of a growing rarity in the individuals of a species. 



Of course a hybrid may be purely accidental, as I believe the 

 case to have been with the cross between the Barn and the Cliff' 

 Swallow which I described some years ago, the result of a mesal- 

 liance between two individuals during the spring flights when 

 numbers of both species are 'hawking' in the air together prior 

 to nesting. But when we see crossing repeatedly performed the 

 question of accident must be set aside and another means of solu- 

 tion sought. 



Let us see how these principles will apply to the genus Hcl- 

 minthophila. Here we have a group of eight species, as has 

 been cited above, none of which are as a rule very abundant, 

 especially when compared with other birds, e. o-., certain species 

 of Dendroica. 



Recalling the distribution of the species, we find that each has 

 a more or less definite area, but their habitats considerably over- 

 lap one another That of the two sub-divisions noted, celata, 

 ritficapilla, and peregrina are the most widely distributed, while 

 chrysoptera, pin?ts, and their allies are much more restricted, and 

 it is in this latter section that we find what is to my mind an evidence 

 of decay. Strictly insectivorous, the Hehninthophilce have come 

 in direct competition with other insectivorous forms, and among 

 them the closely allied and dominant genus Dendroica, with its 

 thirty odd well defined species, whose habits and nature closely 

 resemble the Swamp Warblers in many ways. The pressure ex- 

 erted by Dendroica would be very much greater in the East than 

 in the West, owing to the greater preponderance of individuals 

 and species in the former area ; consequently the more restricted 

 eastern species of Helminthopkila would feel this competition 

 keenly. 



Many of the Dendroicce pursue and capture their food in much 

 the same manner as the Hehninthophilce , and in similar locali- 

 ties ; more than this, the majority are expert fly-catchers, taking 

 mature insects on the wing with much greater readiness and per- 

 sistency than do the species of Swamp Warblers. A glance at 

 the bills of the two will show which is the best adapted for diver- 

 sified work. 



And what has been the upshot of all this? Simply that these 

 restricted species of Helminthophila are succumbing to more 

 wide-spread and better adapted forms, and their decrease in num- 



