July, 1909 
NESTING OF DIOMEDEA NIGRIPES AND D. IMMUTABIUS 
12,1 
average more color, but extremes easily overlap and identity can not be determined 
from the eggs alone. Ten- specimens of each measure in inches as follows: — 
D. ni grifies-. 4.75X2.75, 4.31X2.62, 4.06X2.62, 4.25X2.50, 4.06X2.69, 
4.19X2.75, 4.75X2.75, 4.12X2.69, 4.31X2.75, 3.87X2.69. Average: 4.27X2.68. 
D. immutabilis: 4.00X2.75, 4.37X2.75, 4.31X2.69, 4.25X2.75, 4.31X2.75, 
4.43X2.81, 4.50X2.75, 4.25X2.94, 4.25X2.69, 4.31X2.95. Average: 4.29X2.78. 
The sizes are thus about the same. 
Regarding the nesting habits, Dr. Campbell noted an interesting point of dif- 
ference in the two species; both lay in slight hollows scratcht in the bare sand, 
but immmjabilis usually heaps up this material in a ridge around the “nest”. He 
says “the bird, sitting on the nest and reaching out as far as possible, picks up sand 
in its bill and deposits same around the edge until it is built up four or five inches. 
I noticed the difference in contour of nests of the two species, and as a white pair 
(Laysan) made a nest just beyond my door I was enabled to discover how it was 
done. The building up of the sides results in making the nest higher and also 
provides a shallow ditch all around it, which certainly makes it drier when there 
is rain. ’ ’ 
Each pair of birds — and this applies to both species — rarely lays more than one 
egg in a season, if undisturbed; and if a second egg should be deposited the first 
is thrown out, leaving but one to incubate. If, as was formerly the case, the nests 
are systematically robbed, four eggs are usually supplied by each. 
In 1906, nigripcs arrived the first week in November, immutabilis following a 
few days later, and by the 20th of the month both species had deposited eggs. 
Dr. Campbell believes that the birds pair after arrival, but it would seem that some, 
at least, may have mated previously. 
Incubation lasts about six weeks, both birds taking turns on the nest so that 
the egg is constantly covered. The young are fed, in the well-known manner, by 
regurgitation from the throat of the parent, remaining about the Islands until the 
following June or July, so that the entire reproductive period occupies about one- 
half the year. 
It appears, according to my corresponds nts, that there are about a dozen 
species of birds that commonly breed on these islands, but excepting the albatrosses 
all or nearly all breed during our summer months, chiefly in June and July. 
Since May, 1908, the small detachment of marines, formerly maintained at 
Midway, has been withdrawn, so opportunities for further ornithological observa- 
tions are limited. The islands, however, now constitute a government bird reserve, 
under the protection, I believe, of the Audubon Society, and it is to be hoped that 
they may long afford a harbor of refuge for the feathered wanderers yearly assem- 
bled from the Pacific wastes. 
Washington, D. C. 
THE ONLY KNOWN BREEDING GROUND OF CRECISCUS 
COTURNICULUS 
By A. M. INGERSOLL 
WITH TWO PHOTOS BY THE AUTHOR 
D URING the past four seasons, probably more, a small colony of California 
Black Rails have made their home on a limited area of the weed-covered 
tide lands of San Diego Bay. These breeding grounds are between 
National City and Chula Vista. 
