- 40 only a limited time, and which feed for the most part on crustacea along the beaches. The northern group of birds consisted entirely of terns. Because of their limited migrational tendencies, the terns provide a more representative sample for the determination of continued uptake and metabolism of radioactive materials at Rongelap Atoll than do the shore birds», although in some respects the two groups are similar. In the collections prior to October 1955 the following organs were processed: skin, muscle, bone, lung, liver, kidney, ileum, and thyroid. In the October collections only muscle, bone and liver were taken in an effort to reduce the total number of samples. The average specific activities of muscle, bone and liver of Rongelap and Ailinginae birds are given in Table 11. At the time of the October col- lections the radioactivity levels in the three tissues of the north Rongelap terns were approaching a common value, with the most radioactive tissue (liver) having an activity only 2. 45 times that of the least active tissue (bone). In the Enibuk terns the ratio of highest radioactivity to lowest was 1:3.67. The differences between the highest and lowest levels of activity in the three tissues of the north Rongelap terns for any one collection date have consistently declined since the first collections in March 1954. dates and ratios are as follows: March 26, 1954 - 1: 8.5 July 16, 1954 - -iL: 5.6 December 8, 1954-1: 5.4 January 28-30, 1955 - 1:3.1 October 21, 1955 - 1:2. 5 The