July, 1909 NESTING OF DIOMEDEA NIGRIPES AND D. IMMUTABILIS 123 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:-- J!). nz?ripes: 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. J9. immutabils: 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. immulabilis 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 a? 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, nigrpes arrived the first week in November, immulabilis 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 correspondtnts, 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 lnarines, formerly maintained at Mid?:ay, 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 leathered wanderers yearly assem- bled from the Pacific wastes. WashingIon, j?. C. THE ONLY KNOWN BREEDING GROUND OF CIri'?C-LC(fS CO T U fi? ?I C UL U?S ? By A. M. INGERSOLL ?,VITH TWO PHOTOS BY THE AUTHOR 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.
