LEACH'S FORK-TAILED PETREL. 447 



Ball found this Petrel breeding on several of the Aleutian Islands west 

 of Alaska. He described the burrows as made in the side of a turfy bank, 

 and as from six inches to a foot in length, but always more or less curved 

 to one side. Fresh eggs were found from the 10th of June to the end of 

 July. The male was more often found on the nest than the female : when 

 handled they disgorged a reddish oily fluid of a strong musky smell. 



The Fork-tailed Petrel only lays one egg, which is pure white, with a 

 more or less distinct zone of very minute specks round the large end. The 

 overlying spots are reddish brown, and the underlying ones slightly greyer. 

 Sometimes a few indistinct streaks or dashes of colour, often darker than 

 the spots, occur on the large end of the egg. The eggs vary in length from 

 1'35 to T25 inch, and in breadth from 1*0 to '92 inch. They are readily 

 distinguished from those of the Stormy Petrel, the only species with 

 which they are likely to be confused, by their much larger size. The shell 

 is very fragile, chalky, and without any gloss. Only one brood appears to 

 be reared in the year, and the young chick remains in the nest until it is 

 fledged. 



Leach's Petrel is about the size of a Swift. There is no difference in 

 the colour of the sexes of this species. The adult after the autumn moult 

 has the general colour of the upper parts greyish black, shading into 

 greyish brown on the wing-coverts ; the outer web of the greater wing- 

 coverts and innermost secondaries and the tips of the scapulars are 

 narrowly margined with white ; the sides of the rump and the upper tail- 

 coverts are white, but the longest of the latter are tipped with brown ; 

 the primary-coverts, wings, and tail are nearly black ; the underparts are 

 uniform sooty brown. Bill, legs, and feet black; irides hazel. It is not 

 known that immature birds differ from adults in colour, but the general 

 colour of the plumage becomes brown and faded in summer. Young in 

 down are uniform greyish brown. 



