Power, D. M. (Dept. of Ornithology, Royal Ontario Museum and Dept. of Zoology, University of Toronto, Toronto, Ontario, Canada) 1971. Statistical analysis of character correlations in Brewer's Blackbirds. Syst. Zool., 20:186–203.—Character correlations among 37 skin and skeletal characters within a statistically homogeneous sample of Brewer's blackbirds (Euphagus cyanocephalus) were analyzed by component analysis and average linkage cluster analysis in order to isolate structural and/or functional character sets. Associations were assessed using product-moment correlation coefficients, partial correlations that corrected for a general size factor, and a subset of special partial correlations that corrected for a group factor defining high intercorrelations among limb bone length measurements. With ordinary correlations separate associations were identified for limb bone length, flight feather length, bill length, sternum size, bill width, and limb bone thickness. Some characters were predominantly independent. Partial correlations that corrected for covariation due to the group limb bone length factor indicated special associations among wing bones. An overall size factor is defined as that component which accounts for most of the covariation among all characters. Partial correlations correcting for this factor were analyzed and several size-independent associations emerged. The limb bone length assemblage is in part size-dependent. Size-independent associations include wing bone length, flight feather length, bill length, bill width, and limb bone thickness assemblages, and possibly a partial leg bone length set. Association of three sternal characters appears size-dependent, however a special size-independent association between sternum length and keel height was found. In addition, low-level, size-independent associations are found for pelvis width and bill height characters, as well as between the scapula and coracoid in the pectoral girdle. Results suggest the existence of selective factors that affect the development of functional complex as a whole. Comments are given concerning redundant characters in systematic studies and a temporary solution is offered concerning the problem of adequate sample size in studies of character correlations.