Social Organization and Behavior of the Mexican Jay

The Mexican Jay (Aphelocoma ultramarina) as represented in southern Arizona displays a form of social organization which is shared by no other American species of bird north of the tropical regions.By its characteristic occurrence in flocks the year around it is differentiated from typical territorial species; and by the lack of distinct breeding colonies it is separated from the colonial species.Moreover, its relative lack of intraspecific nest defense within flocks is rarely encountered in other species.Perhaps the aspect of social organization which has aroused the most interest has been the tendency toward a communistic society.Although in territorial and colonial species alike the pair is normally the breeding unit, it has been reported for the Mexican Jay that "even in the breeding season it lives under semicommunal conditions, with mutual interest in all the nests in the community, helping to build and defend its neighbors' nests and young . .." (Bent, 1946: 122).These unusual aspects of social organization stimulated the present study.Its goals have been, first, to establish in detail the actual social organization in one population through color-banding; and, second, to compare the social behavior of the Mexican Jay with that of a congeneric species possessing a more typical territorial system, the Scrub Jay (Aphelocoma coerulescens) .It is hoped this will contribute to the knowledge of the processes concerned in the evolutionary bases of behavior and social organization. METHODSThe area chosen for this investigation was the same one used by Gross (1949) in his study of the Mexican Jay.It lies in Madera Canyon in the Santa Rita Mountains of southern Arizona and spans a range of elevations from 4800 to 5600 feet.Intensive observations were made on two flocks within the canyon.The territory of the first, or Big Rock flock, included the National Forest Service picnic area called Big Rock Camp (5 100 feet).The territory of the second, or Lodge flock, included the Santa Rita Lodge (4900 feet).Both areas were located on the floor of the canyon in the live oak zone and included a stretch of the stream which followed the canyon bed.The periods of field study were February 1 through 6, and April 23 through May 2, 1958.Captives were studied in Berkeley from February, 1958, through January, 1960.Comparisons with the Scrub and Steller (Cyanocitta ste2Zeri) jays refer primarily to the author' s studies of populations in the San Francisco Bay and Carmel Valley areas of California.Jays were readily captured in picnic grounds by using simple, wire-mesh traps baited liberally with conspicuous white bread and sunflower seeds.Each of 50 jays was given a combination of coil-type, plastic, colored, chicken leg-bands which were then cemented shut.No trouble with band loss was experienced.Jays were aged according to the methods of Pitelka (1945) and, in three cases, with the aid of United States Fish and Wildlife Service bands applied in 1953 by Mr. Donald Bleitz.Sex was determined from brood patch and cloaca1 protuberance condition for the Lodge flock, but behavioral characters had to be used for the Big Rock flock since its members were not handled during the breeding season.These characters were (1) the laying of an egg, ( 2) relative time spent on the nest by each member of pair, and (3) industriousness in bringing nest material and working on the nest.