Longitudes and latitudes taken from map entitled "Preliminary Copy," U. S. Petroleum Reserve No. 4, U. S. Geological Survey, March 1948, scale 1-6900.

Wahoo Lake (July 3-11, 1952). Longitude and latitude taken from map entitled "Preliminary Copy," Naval Petroleum Reserve No. 4, U. S. Geological Survey (of same series as map used at Porcupine Lake, see below).

Driftwood (Aug. 27-31, 1952). Longitude and latitude computed from map cited above under Teshekpuk Lake.

Porcupine Lake (July 11-18, 1952). Longitude and latitude computed from map titled "Preliminary Copy," Naval Petroleum Reserve No. 4, compiled by U. S. Geological Survey, May, 1949, Alaska, K6, scale 1:4800.

Porcupine Lake, 146°29'50", 68°51'57", 3140 ft. (July 12-16, 18, 1952).

Chandler Lake (Aug. 9-25, 1951). Longitude and latitude taken from World Aeronautical Chart (63) Brooks Range, U. S. Coast and Geodetic Survey, 5th ed., February 2, 1949.

Gavia adamsii (Gray): Yellow-billed loon.—Specimens, 3: Kaolak (Kuk) River, 159°47'40", 70°11'15", 30 ft., No. 30571, ad. female, July 18, 1951; Wahoo Lake, 146°58', 69°08', 2350 ft. (a breeding pair), No. 31301, ad. male and No. 31302, ad. female, July 9, 1952.

Upon our arrival at Wahoo Lake (July 3, 1952), two yellow-billed loons were swimming, side by side, on the east end of the lake. On July 8, the pair were seen swimming close together 400 feet distant from the nest. It was located on July 4 and held two fresh eggs. Three days later at 3:00 A.M. one of the pair called directly in front of our camp, which was approximately 4000 feet from the nest at the other end of the lake. The call was the first uttered in the area since our arrival. Except for the two instances noted above, only a single loon was seen at any one time almost certainly because the other was sitting on the eggs. At 3:00 P.M. on July 9, by means of a boat, we visited the nesting area; the male was incubating and the female was absent from the area. As we approached to within 30 feet of the nest, the male, conspicuous as it sat upon the nest with neck held low and extended, became nervous. When we were 25 feet away the bird plunged into the lake. His feet and wings beat the water, increasing his speed; he flew to our right approximately 30 feet from the nest and was shot. The nest and eggs were photographed and we left the area. At 5:30 P.M., the female was swimming on the lake in the general area of the nest. In an effort to obtain the bird we pursued her down the middle of the lake, approximately 1000 feet from her nest and in the direction from which we came. Turning shoreward she dived and resurfaced approximately 300 feet in the opposite direction from which she was being pursued. Two additional dives brought her to the vicinity of the nest. No cry was uttered by either of the birds during our pursuit.

Although the female had been incubating two nearly fresh eggs, her ovary, 35 mm long and 19 mm in diameter, contained ova of various sizes up to six mm in diameter. The female measured 850 mm in total length and weighed 4536 grams; the male was 900 mm in total length and weighed 6804 grams.

The nest, approximately 60 cm in diameter, of sedges, grasses and an assortment of plant debris, was on a mound of soil 23 cm above, and 40 cm from, the open water. The cup of the nest measured 37 mm in depth. The site of the nest (southeast corner of the lake) was near the area supporting the most lake trout (Cristivomer namaycush). Between open water of the lake and the shore, 20 feet of sedges and grasses deterred wolves (Canis lupus), red foxes (Vulpes fulva), and caribou (Rangifer arcticus) from molesting the nest; tracks of these mammals were numerous on contiguous shore areas.

The early run-off entering the lake created a variable water level (the overflow decreased 60 per cent in the period July 2 to July 11). The loons lay their eggs when the lake's level is fairly well stabilized. The cotton-grass (Eriophorum) at the latter date was developing white flowers and the sedges, growing in dense stands, were showing springtime green.

The force with which the excrement of the loon is expelled while standing on land, accounts for long white lines upwards of one meter in length. These lines of dried excrement, reaching as far as one and one-tenth meters landward, were noted at several places along the shore.

At Topagaruk on July 9, 1951, a single yellow-billed loon was observed. At Kaolak River (July 12-18, 1951) the yellow-billed loon was occasionally heard at night and, at times in the day. On July 18, an Eskimo, Atanak, accompanied by two companions from Wainwright, shot two loons of this species approximately two miles down the Kaolak River from our camp. They had planned to prepare the birds for their evening meal. With the exception of twelve pebbles averaging 3.5 mm in diameter in the one, the stomachs of the loons were empty. The female was given to us by the Eskimos. It measured 870 mm in total length, 1600 mm in wing spread, and 5897 grams in weight. The ovaries contained many ova, the largest eight mm in diameter. Many of the individual ova were black.

At Porcupine Lake a yellow-billed loon was seen every day (July 13-18, 1952) but was not heard until 8:00 P.M. on July 17; its call was the first since our arrival on July 13. Thereafter its long drawn-out wail or raucous, hilarious call was uttered at intervals in the evening and well toward midnight.

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