452 THE BIRDS OF MAINE 



material before eggs are laid. Incubation is done by both 

 sexes and seems to require sixteen days, as nearly as I have 

 been able to determine, but the error owing to lack of suffi- 

 ciently frequent observation may be a day either way. The 

 old birds are busy indeed after the young appear. The young 

 leave in about sixteen to eighteen days, and it is indeed a 

 noisy session that is held as they venture out of their apart- 

 ment to the outside of the house and, encouraged by the old 

 birds, make short flights. 



The species is essentially a bird of civilization at present, 

 and in Maine occurs only near human dwellings, and is of 

 local distribution. Before the advent of man they must have 

 nested in hollow trees, though none do now. It seems probable 

 that the species has gradually advanced throughout the State 

 with the tide of civilization, or at least it did advance until 

 the importation of English Sparrows forced it backward again. 

 It is found in almost every section of the State, locally, though 

 absent from many localities where it ought to occur. The 

 food consists of insects and is practically all taken on the 

 wing by these aerial birds. They skim along, now high in the 

 air, again close to the surface of the water or over the grass 

 tops in the fields, catching beetles, moths, flies, winged ants, 

 mosquitoes, butterflies and a similar variety of winged insects. 

 Their presence is therefore distinctly beneficial. 



Three to eight pure white eggs are laid, but the usual num- 

 ber is four or five. A set of seven measure as follows: — 0.94 

 X 0.69, 0.91 X 0.68, 0.90 x 0.68, 0.89 x 0.68, 0.91 x 0.68, 

 0.89 X 0.66, 0.88 x 0.66. 



Genus PETROCHELIDON Cabanis. 



612. Petrochelklonlunifrons(SsLy'). Cliff Swallow; Repub- 

 lican; Eave Swallow; Mud Swallow. 



Plumage of adults : crown and back steel blue, very slightly or not at all 

 streaked with white; forehead whitish; throat and sides of head chestnut; 

 grayish ring around neck; upper tail coverts rufous, forming a distinct 



