17 10-8-63 cont. with much vocalization and the bills of the contestants usually end up locked: Then there is tugging, pulling, and lots of noise. Then very quickly it is over with the contestants looking rather bewildered. The fight resumes when the head shaking on both sides begins again. The same head shaking movements are used when the young beg food from the adults. However, a different call accompanies this display, and the adults are usually silent. I have the distinct impression that some of the adults "know" that they are being "taken" from the expressions on their faces after disgorging food. The young's food call is a series of rapid yuk-yuk-yuk-yuk notes given in rhythm to the head movements. Young birds spent a lot of time begging food, and after an adult has been with the hungry waif for several hours and has no more food to give the chick, I believe that they may leave the territory and rest elsewhere to get away from the chick which as often as not follows the adult. 10-9-63 Began making temperature observations on the different microenvironments here and the birds that occupy them ( See Appendix 4 ). Worked at this most of the day and helped Bill set his traps again. Obtained 37 bird temperatures, and fifteen microenvironment temperatures. It seems as if the island is a heat reservoir at night, and lacks heat early in the day. The island seems to reach equilibrium each day at 0930 and 2045, when all environments have about the same temperature, about 27.3 degrees C at 0930, and about 25.1 degrees centigrade at 2045. This daily temperature cycle is, of course, a direct result of the daily weather pattern. However, the relatively d warm lagoon temperature and constant winds seem to keep the island in a very homogeneous temperature state. Except when there is rain, the daily Temperature cycle probably is no more than 7 - 10 degrees centigrade for most of the island where there is vegitation. Bare soil fluctuates more than that. Notes on Sub-Adult Masked Booby Plumages: I have now seen three Subadult Masked Boobys ( all banded, one specimen No. 667-70640 ) showing vestiges of immature plumage. In this plumage the coverts of the secondaries, tertials, upper tail coverts, and occasionally a few of the lower ( posterior ) back feathers show the mottling of black which is characteristic of most of the feathers in Juvenals. This reten- tion of the immature plumage apparently varies considerably with individuals. The iris of the eye is dusky yellow at this plumage also. It is perhaps significant that I have captured only females in this plumage thus far: It again suggests that ♂ birds are more skittish, and are less attached to the breeding grounds.