40 The Wilson Ik-LLEiiN — No. 55. 



evident that while there is always a comnnuniity of interest in 

 the whole colony the aggressive protest against the intruder 

 is confined to the birds immediately interested. In cases of 

 doubt as to whetlier the nest under observation was that of 

 hiruudo or dongaUi it was only necessary to remain quietly 

 near the nest until all but one or two of the birds tired of the 

 demonstration of hostility. The female was invariably the 

 more aggressive. 



Not much of the.incubatiou of the eggs is left to the heat of 

 sun and sand, but the birds brood almost constantly. Eggs 

 left exposed to the sun for any considerable time die. A large 

 number of eggs do not hatch. Some are evidently infertile, 

 but manv die from lack of proper care. Incubatiou evidently 

 begins when the first tgg is laid. 



The first feather rudiments appear as little swellings upon 

 the skin surface on the fifth day of incubation. By the tenth 

 day thev have greatly elongated and turned backward to lie 

 parallel to the skin surface, many of them being pigmented. 

 These rudiments of the first or nestling downs appear first on 

 the tail, then successively forward to the forehead along the 

 feather tracts, except that in the region of the large wing 

 feathers they begin to appear at about the time when those on 

 the lower back are first seen. On the 18th day of incubation 

 the dowai feathers in the region of the outer primaries begin to 

 show enlarged bases beneath the skin. These enlargements 

 are the beginning of the future juvenile flight feathers. When 

 the bird hatches its down feathers are unexpanded and look 

 like wet hairs plastered against the skin. They remain in this 

 condition during the first day after hatching, but on the sec- 

 ond day the enclosing sheath dries and splits and the liberated 

 and dried down barbs expand and cover the skin surface with a 

 soft, fluffy i^lumage. On the third (la\- after hatching the flight 

 feathers appear at the surface of the skin and in their further 

 growth push the down feathers out of their pockets. At first 

 the new feather is enclosed by a horny sheath which keeps it 

 in the "pin feather" form, with the tuft of down sticking to its 

 pointed tip. Tn three or four days the horny sheath dries and 

 splits away from the tip and the new feather flattens out into 



