On June 14, 1952, at Birnirk mounds, when snow still covered most of the ground, Baird's sandpipers were already established on territories. A nest of four eggs was examined 1/4 mile southeast of the Arctic Research Laboratory on July 4. The female left the nest when the observer approached to within 20 feet and flew directly toward him and then dropped to the ground and pretended to have a broken wing. We pursued this bird for 50 feet before she took flight. The male, which flew at a much greater speed than the female, was nearby and soon joined her in flight. The female repelled her mate by chasing him, but the male persisted in accompanying her. If one or more males of this species (on one occasion as many as five) approached the territory of these nesting birds, the male would leave the female and chase the trespassers. On one occasion, after we left the nesting area, the female returned to the nest after approximately four minutes. Her approach to it was direct and without hesitation. After 1/2 hour we returned to the nest and the male was standing one foot away from the brooding female with his head resting on his wing. The male, followed by the female, left the nest and feigned injury. Shore-birds and water birds were more numerous on this date on the tundra and lakes nearer the Arctic Ocean (in the Point Barrow area) than in the direction of the Brooks Range. At Topagaruk (July 5-10, 1952) adults of this species were the fourth most common bird, representing four per cent of the avian population. They were near lakes among polygons some of which had low centers whereas others had high centers. One bird had a nest and four eggs approximately 150 feet from an oil derrick, surrounded on all sides by the tracks of vehicles. This bird feigned injury at the nest notably more than did Baird's sandpipers that inhabited undisturbed tundra beyond. Three adult males, shot at Topagaruk (July 7-10, 1951), averaged 44(42-47) grams in weight and had testes averaging 3.5(3.0-4.5) mm long. Two females, collected in the same period and at the same place averaged 44 grams in weight. The largest ovum was one mm in diameter and the largest ovary three mm long. Other occurrences were: Kaolak River, July 12-18, 1951 (four juveniles observed in one four hour field trip July 15); Lake Schrader, July 24-28, 1952; Point Barrow, July 27, 1951 (most common shore-bird at fresh-water ponds adjacent to the Arctic Ocean); 2 mi. S Wahoo Lake, on a high divide between the Ivashak and Sadlerochit rivers, July 8, 1952; Lake Schrader, July 23-31, 1952 (active at all hours); S end Lake Peters, August 1 and 2 but not seen there later. +Erolia alpina pacifica+ (Coues): Dunlin.--Specimens, 21: Barrier Lake, NE Teshekpuk Lake, 153 deg.05'40", 70 deg.39'40", 8 ft., 1, No. 30661, ad. male, Aug. 1, 1951; Topagaruk River, 155 deg.48', 70 deg.34', 10 ft., 20, Nos. 30662-30681, 12 ad. males and 8 ad. females, July 6-9, 1951.