LIFE HISTORIES OF NORTH AMERICAN PETRELS AND PELICANS. 75 



age 52.5 by 3G.2 millimeters; the eggs showing the four extremes 

 measure 57.3 by 40.8, 49.2 by 35.2, and 50 by 34 millimeters. 



Young. — Incubation is carried on by both parents, and before the 

 egg is laid both occupy the hole together. Bonhote (1903) says "the 

 parent apparently does not brood the young, but merely sits beside 

 it during the first day or two of its existence, after which it is left 

 alone during the daytime." 



Plumages. — The downy young is of a dusky gray color, whitish 

 on the abdomen. The adult is only 12 inches in length while the 

 greater shearwater is 20 inches. The upper parts including the wings 

 and tail are a dark, sooty, brownish black; the under parts white; 

 the sides of the breast grayish white. The bill is black. Godman 

 (1907) gives the following critical analysis of the differences between 

 this form and P. ohscuncs: 



The measurement of these two forms iifford no characters for specific separa- 

 tion though P. auduboni would appear to have a slightly larger tarsus than 

 P. obsciuus. I find that the chief difference between the eastern and western 

 birds lie in the browner color of P. auduhoni, which is never so black as 

 P. ohscurus. The patch above the thighs is brown in the former bird, not black, 

 and the band round the edge of the wing below is browner, and less distinct 

 than P. ohscurus. 



Behavior. — About the breeding ground, the birds are seen and 

 heard only at night, when they appear to be very active. The day- 

 time is spent by those wdio are not on the eggs at a distance on the 

 sea generally out of sight of land, where they rest on the water in 

 large flocks. At times they are very shy, but in the Martinique Chan- 

 nel the birds are said to be so bold as to attempt to rob the fishermen 

 of their fish in the canoes. Audubon (18^:0) says they skim low over 

 the water near bunches of gulf weeds. 



Flap their wings six or seven times in succession and then sail for three 

 or four seconds with great ease, having their tail much spread and their long 

 wings extended at right angles with the body. On approaching a mass of weeds, 

 they raise their wings obliquely, drop their legs and feet, run as it were on the 

 water, and at length alight in the sea, where they swim with as much ease as 

 ducks, and dive freely, at times passing several feet under the surface In 

 pursuit of fishes, which, on perceiving their enemy, swim off but are frequently 

 seized with great agility. Four or five, sometimes fifteen or twenty, of these birds 

 will thus alight, and, during their stay about the weeds, dive, flutter, and swim 

 with all the gaiety of a flock of ducks, newly alighted in a pond. * * * At 

 times, as if by way of resting themselves, they alighted, swam lightly, and 

 dipped their bills frequently in the water, in the manner of mergansers. 



At the breeding grounds, according to Bryant (18G1), "all night 

 long their mournful cries can be heard." Bonhote (1903) says that 

 he never saw the birds outside their holes, " nor could I distinguish 

 their cries at night from those of the sooties." Wells says, in his 



