+Stercorarius parasiticus+ (Linnaeus): Parasitic jaeger.--Specimens, 3: Topagaruk River, 155 deg.48', 70 deg.34, 10 ft., 2, Nos. 30732-30733, ad. females, July 6, 8, 1951; Kaolak, 160 deg.14'51", 69 deg.56'00", 178 ft., 1, No. 30731, ad. male, July 21, 1951. At Topagaruk (July 5-10, 1951) parasitic jaegers ranged over nearly all plant and animal associations, but flew more frequently over polygons with low centers than elsewhere. Data on two adult females, shot on July 6 and 8, in that order are as follows: weight, 525, 320 grams; largest ovum, 3, 1 mm; length of ovary ----, 5.5 mm. The bird killed on July 6 was in the black color phase. At Kaolak River (July 12-18, 1951) the parasitic jaeger was the least common of the three species of jaegers. At Kaolak (July 21-27, 1951) two birds nested near camp while others passed through the area. These passing birds generally were seen singly or in pairs; long-tailed jaegers commonly are in groups of four or five. The parasitic jaegers were not so noisy nor so much given to chasing others of their own species as were long-tailed jaegers. Several single birds hunted in areas of sedges and grasses that yielded lemmings. On July 21, a parasitic jaeger was flying with three glaucous gulls, and demonstrating its usual flight tactics of gliding, climbing and swooping as it accompanied the gulls. An adult male shot on July 21, weighed 460 grams. On alluvial outwash at the southwest end of Lake Schrader (July 27, 1952) a male and female parasitic jaeger defended their territory by diving at us. Periodically both birds alighted approximately 60 feet away and each pretended to have a crippled wing for approximately a minute. The female acted as if herding the young but was not. On each of our daily inspections an adult defended the area. In a period of four days the area defended was shifted approximately 1/5 of a mile south in the marsh area adjacent to the lake. Parasitic jaegers were noted in the Lake Schrader area from July 23 to July 31 inclusive. At Barrier Lake (July 30, 1951) two parasitic jaegers were harassing a glaucous gull that responded as if being attacked by a hawk. The plunging of the jaeger continued while the gull was flying 300 feet horizontally. One other jaeger chased a glaucous gull for one-fourth of a mile and finally having caught up with it dove at the gull several times, each time almost making contact. From our camp on Barrier Lake (July 29-Aug. 4, 1951) we watched parasitic jaegers hunt along the south end of the lake, following precisely the edge of the water. The wind drove debris to the south end of the lake. The long-tailed jaeger was the more numerous here; it flew along ridges and over marshes. On July 30, a single jaeger flew over the lake and after hovering above a young Arctic loon, which had strayed from its parent, dove down and picked it up. Three other parasitic jaegers arrived and competed for the prey.