24 INSECTIVOROUS BIRDS 



ft 



TREE MARTIN 



(Tree Swallow), 



Petroclielidon nigricans, Vieill. 



Pet-rd-kel'i-don nig'ri-kans. 

 Petros, a rock ; chelidon, a swallow ; nigricans, blackish. 



GoLLOCALiA ARBOREA, Gould, "Birds of Australia," fol., vol. ii., 



pi. 14. 



Geographical Distribution. — Areas 2, 3, 4, 5, 6, 7, 9. 



Key to the Species.— Under surface whitish ; throat whitish, with 

 tiny black streaks ; frontal band sandy buff ; rump whity- 

 brown ; tail forked ; nostrils without any superior membrane, 

 round and exposed. 



Of every hundred intelligent people who see martins in 

 the woods or near bridges I feel sure ninety-eight never 

 distinguish this species from the second martin of the genus 

 (P. ariel, Gld.) That is because there is practically but 

 one difference, and in the distance not discoverable without 

 field-glasses. One has the forehead rufous only, the other 

 has the forehead and crown rufous, each characteristic 

 being ahvays constant. Both have similar ways, and very 

 often occupy the same nature of surroundings. P. nigricans, 

 as well as I know, stays for the winter and breeds in holes 

 in trees, while P. ariel prefers creeks and cliffs against 

 which to build, or bridges, under which they colonize and 

 nest. In a way it is a migratory bird, leaving after Feb- 

 ruary and returning in August or September. Being 

 strictly arboreal, it hunts in flocks, feeding largely upon 

 micro-insecta. In this respect it is invaluable as an insect 

 exterminator, functioning as few other birds than swallows 

 can do. When each ninth or tenth generation of the 

 aphis comes into existence the birds display wonderful 



