ITINERARY 16 October, 1967 1100 hours (+7 time) Depart San Diego, Calif. 07 November 2359 Arrive Manzanillo, Mexico 10 November 1100 Depart Manzanillo 03 December ca. 0200 Arrive San Diego The following report summarizes bird and mammal observations conducted aboard the R/V DAVID STARR JORDAN during EASTROPAC Monitor Cruise No. 50 from 17 October to 03 December, 1967. During this period diurnal observa- tions were maintained for 297.9 hours over 3465 nautical miles. A total of 14463 seabirds was recorded. No observations were made when the ship was "on station", and collections were restricted to times when they would not interfere with primary objectives of the cruise. In this report the cruise track (see map one) has been divided into water-type areas (see map two) in order to facilitate discussion. These divisions are based primarily on oceanographic differences, but occasion- ally avian differences were used. During October and November the distribution of birds within the area covered by the monitor cruise was quite graphic, but as little summarized data are available at present, no explanations beyond very crude correlations will be attempted. However the reader is urged to compare species densities and distribution carefully, especially for tropicbirds, Wedge-tailed Shear- water, and species in the genus Pterodroma. From these distributions it appears that the cruise track transversed rather prominent ecological zones, especially in the western portions of the cruise. Additional dis- cussions pertaining to ecological factors will be included elsewhere in this report. For now it should be mentioned that few patterns of abundance were noted within a single species which could be correlated to specific oceanographic or biological data as available in crude form at the time of this report. This is not to say that such patterns did not exist, but rather is intended to suggest that they were obscured in some areas by the influence of various combinations of environmental variables as well as variable responses by different species to habitat changes. METHODS Observations were maintained from the flying bridge which afforded a 360 degree horizon and an excellent angle for identification of birds fairly close to the ship. Because I was the only P.O.B.S.P. observer a- board, it was not possible to maintain continuous binocular surveillance during all daylight periods. Thus sightings were largely of birds which could be seen with the unaided eye with binocular support only for identi- fication. Hours of observation were limited to daylight periods when the ship was underway.