Nov., 1909 BIRD NOTES FROM SAN LUIS OBISPO COUNTY 187

intimation of danger and will appear on a point of rock some distance away, where she will be joined by her mate. Altogether we collected four sets of this species. Three of these were of three eggs each and one of two eggs. To secure two of these sets I had to swim thru a dangerous urf and land on jagged rocks; and the other two were on the top of rocky pinnacles which were all but inaccessible. The nests are placed on the lea side of a rock or projection sheltered from the prevailing wind, sometimes only a few feet above high water and at other times far above the reach of the flying spray. They are shallow cavi- ties in the rock or thin soil, thickly lined with sharp chips of rock evidently carried by the birds. Numerous scratches on the shells of the eggs show that they are frequently turned over by the birds who probably rely to some extent on the heat of the sun as an assistance in incubation. The birds subsist principally on mussels and limpets, and the ease with which they pry them from the rocks with the sharp, chisel-like bill furnishes a striking example of the natural law of adaptation to surroundings. The rocks around the fiesting sites are covered with the shells of molluscs brought there by the birds. The statement that this species nests on gravelly beaches is erroneous as regards this locality. The first set of eggs was taken May 14, and was about half incu- bated. .It was situated on a large flat-topt rock very difficult of access. There were breeding on the top of the same rock four pairs of Western Gulls and a colony of Brandt Cormorants; while on the precipitous .sides were numerous nests of the Baird Cormorant; and in the caves at the base of the rock were two or three pairs of Sea Pigeons. The other three sets were taken on May 15, 16 and 17, respective- ly, and were on isolated rocks, the Oystercatchers being the sole inhabitants. In ground color the eggs vary from grayish olive to greenish, spotted and blotcht with black and dark brown, with lavender shell markings. Thirteen eggs measure in inches: Maximum, 2.38>(1.58; minimum, 2.08X1.45; average 2.24X1.52. Los Angeles, Cahfornia. A LIFE HISTORY OF THE NORTHERN BALD EAGLE By JOSEPH DIXON WITH FOUR PHOTOS BY ANNIE M. AI,EXANDER KNOW. of no other Alaskan bird which seems to be more in keeping with the country than the Northern Bald Eagle (trtra/ia, etus /eucocepha/us alascanus). While this bird is by no means restricted to the shore line of the Pacific be- tween the southern boundary of Alaska and the base of the Alaska Peninsula, still I believe that it may be truthfully stated that nowhere else does it find a more con- genial home or breed in larger numbers than along this thousand-mile stretch of islands, inlets and glacier-scoured coast. In size, this eagle is considerably the superior of its cousins in "the states", since it is not uncommon to find female eagles that are more than thirty-seven inches in length, with a spread of seven feet and a half, or better. The males are, of course, quite a little smaller than the females and rarely equal the smaller fe- males in size. The largest female that I secured had a spread of seven feet and nine inches; length, thirty-seven inches. The males seemed to average about a foot less than this inspread, and were about thirt7-six inches in length. I was inter-